32 files changed, 1439 insertions, 321 deletions

diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index 853605f5c2..10b27cfe92 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -69,6 +69,7 @@ var depsRules = `
 
 	internal/goarch < internal/abi;
 	internal/byteorder, internal/cpu, internal/goarch < internal/chacha8rand;
+	internal/goarch, math/bits < internal/strconv;
 
 	# RUNTIME is the core runtime group of packages, all of them very light-weight.
 	internal/abi,
@@ -80,6 +81,7 @@ var depsRules = `
 	internal/goexperiment,
 	internal/goos,
 	internal/profilerecord,
+	internal/strconv,
 	internal/trace/tracev2,
 	math/bits,
 	structs
diff --git a/src/strconv/atob.go b/src/internal/strconv/atob.go
index 0a495008d7..cbeba7f8bc 100644
--- a/src/strconv/atob.go
+++ b/src/internal/strconv/atob.go
@@ -14,7 +14,7 @@ func ParseBool(str string) (bool, error) {
 	case "0", "f", "F", "false", "FALSE", "False":
 		return false, nil
 	}
-	return false, syntaxError("ParseBool", str)
+	return false, ErrSyntax
 }
 
 // FormatBool returns "true" or "false" according to the value of b.
diff --git a/src/strconv/atob_test.go b/src/internal/strconv/atob_test.go
index 40d43a9f8f..61f543df30 100644
--- a/src/strconv/atob_test.go
+++ b/src/internal/strconv/atob_test.go
@@ -6,7 +6,7 @@ package strconv_test
 
 import (
 	"bytes"
-	. "strconv"
+	. "internal/strconv"
 	"testing"
 )
 
@@ -36,23 +36,8 @@ var atobtests = []atobTest{
 func TestParseBool(t *testing.T) {
 	for _, test := range atobtests {
 		b, e := ParseBool(test.in)
-		if test.err != nil {
-			// expect an error
-			if e == nil {
-				t.Errorf("ParseBool(%s) = nil; want %s", test.in, test.err)
-			} else {
-				// NumError assertion must succeed; it's the only thing we return.
-				if e.(*NumError).Err != test.err {
-					t.Errorf("ParseBool(%s) = %s; want %s", test.in, e, test.err)
-				}
-			}
-		} else {
-			if e != nil {
-				t.Errorf("ParseBool(%s) = %s; want nil", test.in, e)
-			}
-			if b != test.out {
-				t.Errorf("ParseBool(%s) = %t; want %t", test.in, b, test.out)
-			}
+		if b != test.out || e != test.err {
+			t.Errorf("ParseBool(%s) = %v, %v, want %v, %v", test.in, b, e, test.out, test.err)
 		}
 	}
 }
diff --git a/src/strconv/atoc.go b/src/internal/strconv/atoc.go
index 560bd7920d..52f2fc82af 100644
--- a/src/strconv/atoc.go
+++ b/src/internal/strconv/atoc.go
@@ -4,23 +4,6 @@
 
 package strconv
 
-import "internal/stringslite"
-
-const fnParseComplex = "ParseComplex"
-
-// convErr splits an error returned by parseFloatPrefix
-// into a syntax or range error for ParseComplex.
-func convErr(err error, s string) (syntax, range_ error) {
-	if x, ok := err.(*NumError); ok {
-		x.Func = fnParseComplex
-		x.Num = stringslite.Clone(s)
-		if x.Err == ErrRange {
-			return nil, x
-		}
-	}
-	return err, nil
-}
-
 // ParseComplex converts the string s to a complex number
 // with the precision specified by bitSize: 64 for complex64, or 128 for complex128.
 // When bitSize=64, the result still has type complex128, but it will be
@@ -47,8 +30,6 @@ func ParseComplex(s string, bitSize int) (complex128, error) {
 		size = 32 // complex64 uses float32 parts
 	}
 
-	orig := s
-
 	// Remove parentheses, if any.
 	if len(s) >= 2 && s[0] == '(' && s[len(s)-1] == ')' {
 		s = s[1 : len(s)-1]
@@ -59,10 +40,10 @@ func ParseComplex(s string, bitSize int) (complex128, error) {
 	// Read real part (possibly imaginary part if followed by 'i').
 	re, n, err := parseFloatPrefix(s, size)
 	if err != nil {
-		err, pending = convErr(err, orig)
-		if err != nil {
+		if err != ErrRange {
 			return 0, err
 		}
+		pending = err
 	}
 	s = s[n:]
 
@@ -88,20 +69,20 @@ func ParseComplex(s string, bitSize int) (complex128, error) {
 		}
 		fallthrough
 	default:
-		return 0, syntaxError(fnParseComplex, orig)
+		return 0, ErrSyntax
 	}
 
 	// Read imaginary part.
 	im, n, err := parseFloatPrefix(s, size)
 	if err != nil {
-		err, pending = convErr(err, orig)
-		if err != nil {
+		if err != ErrRange {
 			return 0, err
 		}
+		pending = err
 	}
 	s = s[n:]
 	if s != "i" {
-		return 0, syntaxError(fnParseComplex, orig)
+		return 0, ErrSyntax
 	}
 	return complex(re, im), pending
 }
diff --git a/src/strconv/atoc_test.go b/src/internal/strconv/atoc_test.go
index 4c1aad0900..0a7741a4cc 100644
--- a/src/strconv/atoc_test.go
+++ b/src/internal/strconv/atoc_test.go
@@ -7,8 +7,7 @@ package strconv_test
 import (
 	"math"
 	"math/cmplx"
-	"reflect"
-	. "strconv"
+	. "internal/strconv"
 	"testing"
 )
 
@@ -188,30 +187,24 @@ func TestParseComplex(t *testing.T) {
 	}
 	for i := range tests {
 		test := &tests[i]
-		if test.err != nil {
-			test.err = &NumError{Func: "ParseComplex", Num: test.in, Err: test.err}
+		c, e := ParseComplex(test.in, 128)
+		if !sameComplex(c, test.out) || e != test.err {
+			t.Errorf("ParseComplex(%s, 128) = %v, %v, want %v, %v", test.in, c, e, test.out, test.err)
 		}
-		got, err := ParseComplex(test.in, 128)
-		if !reflect.DeepEqual(err, test.err) {
-			t.Fatalf("ParseComplex(%q, 128) = %v, %v; want %v, %v", test.in, got, err, test.out, test.err)
-		}
-		if !(cmplx.IsNaN(test.out) && cmplx.IsNaN(got)) && got != test.out {
-			t.Fatalf("ParseComplex(%q, 128) = %v, %v; want %v, %v", test.in, got, err, test.out, test.err)
-		}
-
 		if complex128(complex64(test.out)) == test.out {
-			got, err := ParseComplex(test.in, 64)
-			if !reflect.DeepEqual(err, test.err) {
-				t.Fatalf("ParseComplex(%q, 64) = %v, %v; want %v, %v", test.in, got, err, test.out, test.err)
-			}
-			got64 := complex64(got)
-			if complex128(got64) != test.out {
-				t.Fatalf("ParseComplex(%q, 64) = %v, %v; want %v, %v", test.in, got, err, test.out, test.err)
+			c, e := ParseComplex(test.in, 64)
+			c64 := complex64(c)
+			if !sameComplex(complex128(c64) , test.out) || e != test.err {
+				t.Errorf("ParseComplex(%s, 64) = %v, %v, want %v, %v", test.in, c, e, test.out, test.err)
 			}
 		}
 	}
 }
 
+func sameComplex(c1, c2 complex128) bool {
+	return cmplx.IsNaN(c1) && cmplx.IsNaN(c2) || c1 == c2
+}
+
 // Issue 42297: allow ParseComplex(s, not_32_or_64) for legacy reasons
 func TestParseComplexIncorrectBitSize(t *testing.T) {
 	const s = "1.5e308+1.0e307i"
diff --git a/src/strconv/atof.go b/src/internal/strconv/atof.go
index c05d298257..ada45dc0aa 100644
--- a/src/strconv/atof.go
+++ b/src/internal/strconv/atof.go
@@ -10,8 +10,6 @@ package strconv
 //   2) Multiply/divide decimal by powers of two until in range [0.5, 1)
 //   3) Multiply by 2^precision and round to get mantissa.
 
-import "math"
-
 var optimize = true // set to false to force slow-path conversions for testing
 
 // commonPrefixLenIgnoreCase returns the length of the common
@@ -58,11 +56,11 @@ func special(s string) (f float64, n int, ok bool) {
 			n = 3
 		}
 		if n == 3 || n == 8 {
-			return math.Inf(sign), nsign + n, true
+			return inf(sign), nsign + n, true
 		}
 	case 'n', 'N':
 		if commonPrefixLenIgnoreCase(s, "nan") == 3 {
-			return math.NaN(), 3, true
+			return nan(), 3, true
 		}
 	}
 	return 0, 0, false
@@ -546,7 +544,7 @@ func atofHex(s string, flt *floatInfo, mantissa uint64, exp int, neg, trunc bool
 	if exp > maxExp { // infinity and range error
 		mantissa = 1 << flt.mantbits
 		exp = maxExp + 1
-		err = rangeError(fnParseFloat, s)
+		err = ErrRange
 	}
 
 	bits := mantissa & (1<<flt.mantbits - 1)
@@ -555,9 +553,9 @@ func atofHex(s string, flt *floatInfo, mantissa uint64, exp int, neg, trunc bool
 		bits |= 1 << flt.mantbits << flt.expbits
 	}
 	if flt == &float32info {
-		return float64(math.Float32frombits(uint32(bits))), err
+		return float64(float32frombits(uint32(bits))), err
 	}
-	return math.Float64frombits(bits), err
+	return float64frombits(bits), err
 }
 
 const fnParseFloat = "ParseFloat"
@@ -569,7 +567,7 @@ func atof32(s string) (f float32, n int, err error) {
 
 	mantissa, exp, neg, trunc, hex, n, ok := readFloat(s)
 	if !ok {
-		return 0, n, syntaxError(fnParseFloat, s)
+		return 0, n, ErrSyntax
 	}
 
 	if hex {
@@ -603,12 +601,12 @@ func atof32(s string) (f float32, n int, err error) {
 	// Slow fallback.
 	var d decimal
 	if !d.set(s[:n]) {
-		return 0, n, syntaxError(fnParseFloat, s)
+		return 0, n, ErrSyntax
 	}
 	b, ovf := d.floatBits(&float32info)
-	f = math.Float32frombits(uint32(b))
+	f = float32frombits(uint32(b))
 	if ovf {
-		err = rangeError(fnParseFloat, s)
+		err = ErrRange
 	}
 	return f, n, err
 }
@@ -620,7 +618,7 @@ func atof64(s string) (f float64, n int, err error) {
 
 	mantissa, exp, neg, trunc, hex, n, ok := readFloat(s)
 	if !ok {
-		return 0, n, syntaxError(fnParseFloat, s)
+		return 0, n, ErrSyntax
 	}
 
 	if hex {
@@ -654,12 +652,12 @@ func atof64(s string) (f float64, n int, err error) {
 	// Slow fallback.
 	var d decimal
 	if !d.set(s[:n]) {
-		return 0, n, syntaxError(fnParseFloat, s)
+		return 0, n, ErrSyntax
 	}
 	b, ovf := d.floatBits(&float64info)
-	f = math.Float64frombits(b)
+	f = float64frombits(b)
 	if ovf {
-		err = rangeError(fnParseFloat, s)
+		err = ErrRange
 	}
 	return f, n, err
 }
@@ -693,8 +691,8 @@ func atof64(s string) (f float64, n int, err error) {
 // [floating-point literals]: https://go.dev/ref/spec#Floating-point_literals
 func ParseFloat(s string, bitSize int) (float64, error) {
 	f, n, err := parseFloatPrefix(s, bitSize)
-	if n != len(s) && (err == nil || err.(*NumError).Err != ErrSyntax) {
-		return 0, syntaxError(fnParseFloat, s)
+	if n != len(s) {
+		return 0, ErrSyntax
 	}
 	return f, err
 }
diff --git a/src/strconv/atof_test.go b/src/internal/strconv/atof_test.go
index 7b287b4219..dd0b4dd6ef 100644
--- a/src/strconv/atof_test.go
+++ b/src/internal/strconv/atof_test.go
@@ -8,7 +8,7 @@ import (
 	"math"
 	"math/rand"
 	"reflect"
-	. "strconv"
+	. "internal/strconv"
 	"strings"
 	"sync"
 	"testing"
@@ -446,21 +446,6 @@ func initAtof() {
 }
 
 func initAtofOnce() {
-	// The atof routines return NumErrors wrapping
-	// the error and the string. Convert the table above.
-	for i := range atoftests {
-		test := &atoftests[i]
-		if test.err != nil {
-			test.err = &NumError{"ParseFloat", test.in, test.err}
-		}
-	}
-	for i := range atof32tests {
-		test := &atof32tests[i]
-		if test.err != nil {
-			test.err = &NumError{"ParseFloat", test.in, test.err}
-		}
-	}
-
 	// Generate random inputs for tests and benchmarks
 	if testing.Short() {
 		atofRandomTests = make([]atofSimpleTest, 100)
@@ -497,7 +482,7 @@ func TestParseFloatPrefix(t *testing.T) {
 		// correctly as "inf" with suffix.
 		for _, suffix := range []string{" ", "q", "+", "-", "<", "=", ">", "(", ")", "i", "init"} {
 			in := test.in + suffix
-			_, n, err := ParseFloatPrefix(in, 64)
+			_, n, err := parseFloatPrefix(in, 64)
 			if err != nil {
 				t.Errorf("ParseFloatPrefix(%q, 64): err = %v; want no error", in, err)
 			}
diff --git a/src/strconv/eisel_lemire.go b/src/internal/strconv/atofeisel.go
index 7bc9c71a40..10b8c96bba 100644
--- a/src/strconv/eisel_lemire.go
+++ b/src/internal/strconv/atofeisel.go
@@ -18,7 +18,6 @@ package strconv
 // https://github.com/nigeltao/parse-number-fxx-test-data/blob/5280dcfccf6d0b02a65ae282dad0b6d9de50e039/script/test-go-strconv.go
 
 import (
-	"math"
 	"math/bits"
 )
 
@@ -29,7 +28,7 @@ func eiselLemire64(man uint64, exp10 int, neg bool) (f float64, ok bool) {
 	// Exp10 Range.
 	if man == 0 {
 		if neg {
-			f = math.Float64frombits(0x8000000000000000) // Negative zero.
+			f = float64frombits(0x8000000000000000) // Negative zero.
 		}
 		return f, true
 	}
@@ -88,7 +87,7 @@ func eiselLemire64(man uint64, exp10 int, neg bool) (f float64, ok bool) {
 	if neg {
 		retBits |= 0x8000000000000000
 	}
-	return math.Float64frombits(retBits), true
+	return float64frombits(retBits), true
 }
 
 func eiselLemire32(man uint64, exp10 int, neg bool) (f float32, ok bool) {
@@ -104,7 +103,7 @@ func eiselLemire32(man uint64, exp10 int, neg bool) (f float32, ok bool) {
 	// Exp10 Range.
 	if man == 0 {
 		if neg {
-			f = math.Float32frombits(0x80000000) // Negative zero.
+			f = float32frombits(0x80000000) // Negative zero.
 		}
 		return f, true
 	}
@@ -163,5 +162,5 @@ func eiselLemire32(man uint64, exp10 int, neg bool) (f float32, ok bool) {
 	if neg {
 		retBits |= 0x80000000
 	}
-	return math.Float32frombits(uint32(retBits)), true
+	return float32frombits(uint32(retBits)), true
 }
diff --git a/src/strconv/atoi.go b/src/internal/strconv/atoi.go
index 83e931fe24..5bc259e7e5 100644
--- a/src/strconv/atoi.go
+++ b/src/internal/strconv/atoi.go
@@ -4,11 +4,6 @@
 
 package strconv
 
-import (
-	"errors"
-	"internal/stringslite"
-)
-
 // lower(c) is a lower-case letter if and only if
 // c is either that lower-case letter or the equivalent upper-case letter.
 // Instead of writing c == 'x' || c == 'X' one can write lower(c) == 'x'.
@@ -17,47 +12,28 @@ func lower(c byte) byte {
 	return c | ('x' - 'X')
 }
 
-// ErrRange indicates that a value is out of range for the target type.
-var ErrRange = errors.New("value out of range")
-
-// ErrSyntax indicates that a value does not have the right syntax for the target type.
-var ErrSyntax = errors.New("invalid syntax")
-
-// A NumError records a failed conversion.
-type NumError struct {
-	Func string // the failing function (ParseBool, ParseInt, ParseUint, ParseFloat, ParseComplex)
-	Num  string // the input
-	Err  error  // the reason the conversion failed (e.g. ErrRange, ErrSyntax, etc.)
-}
-
-func (e *NumError) Error() string {
-	return "strconv." + e.Func + ": " + "parsing " + Quote(e.Num) + ": " + e.Err.Error()
-}
-
-func (e *NumError) Unwrap() error { return e.Err }
-
-// All ParseXXX functions allow the input string to escape to the error value.
-// This hurts strconv.ParseXXX(string(b)) calls where b is []byte since
-// the conversion from []byte must allocate a string on the heap.
-// If we assume errors are infrequent, then we can avoid escaping the input
-// back to the output by copying it first. This allows the compiler to call
-// strconv.ParseXXX without a heap allocation for most []byte to string
-// conversions, since it can now prove that the string cannot escape Parse.
-
-func syntaxError(fn, str string) *NumError {
-	return &NumError{fn, stringslite.Clone(str), ErrSyntax}
-}
-
-func rangeError(fn, str string) *NumError {
-	return &NumError{fn, stringslite.Clone(str), ErrRange}
-}
+type Error int
 
-func baseError(fn, str string, base int) *NumError {
-	return &NumError{fn, stringslite.Clone(str), errors.New("invalid base " + Itoa(base))}
-}
+const (
+	_ Error = iota
+	ErrRange
+	ErrSyntax
+	ErrBase
+	ErrBitSize
+)
 
-func bitSizeError(fn, str string, bitSize int) *NumError {
-	return &NumError{fn, stringslite.Clone(str), errors.New("invalid bit size " + Itoa(bitSize))}
+func (e Error) Error() string {
+	switch e {
+	case ErrRange:
+		return "value out of range"
+	case ErrSyntax:
+		return "invalid syntax"
+	case ErrBase:
+		return "invalid base"
+	case ErrBitSize:
+		return "invalid bit size"
+	}
+	return "unknown error"
 }
 
 const intSize = 32 << (^uint(0) >> 63)
@@ -74,7 +50,7 @@ func ParseUint(s string, base int, bitSize int) (uint64, error) {
 	const fnParseUint = "ParseUint"
 
 	if s == "" {
-		return 0, syntaxError(fnParseUint, s)
+		return 0, ErrSyntax
 	}
 
 	base0 := base == 0
@@ -105,13 +81,13 @@ func ParseUint(s string, base int, bitSize int) (uint64, error) {
 		}
 
 	default:
-		return 0, baseError(fnParseUint, s0, base)
+		return 0, ErrBase
 	}
 
 	if bitSize == 0 {
 		bitSize = IntSize
 	} else if bitSize < 0 || bitSize > 64 {
-		return 0, bitSizeError(fnParseUint, s0, bitSize)
+		return 0, ErrBitSize
 	}
 
 	// Cutoff is the smallest number such that cutoff*base > maxUint64.
@@ -141,29 +117,29 @@ func ParseUint(s string, base int, bitSize int) (uint64, error) {
 		case 'a' <= lower(c) && lower(c) <= 'z':
 			d = lower(c) - 'a' + 10
 		default:
-			return 0, syntaxError(fnParseUint, s0)
+			return 0, ErrSyntax
 		}
 
 		if d >= byte(base) {
-			return 0, syntaxError(fnParseUint, s0)
+			return 0, ErrSyntax
 		}
 
 		if n >= cutoff {
 			// n*base overflows
-			return maxVal, rangeError(fnParseUint, s0)
+			return maxVal, ErrRange
 		}
 		n *= uint64(base)
 
 		n1 := n + uint64(d)
 		if n1 < n || n1 > maxVal {
 			// n+d overflows
-			return maxVal, rangeError(fnParseUint, s0)
+			return maxVal, ErrRange
 		}
 		n = n1
 	}
 
 	if underscores && !underscoreOK(s0) {
-		return 0, syntaxError(fnParseUint, s0)
+		return 0, ErrSyntax
 	}
 
 	return n, nil
@@ -198,11 +174,10 @@ func ParseInt(s string, base int, bitSize int) (i int64, err error) {
 	const fnParseInt = "ParseInt"
 
 	if s == "" {
-		return 0, syntaxError(fnParseInt, s)
+		return 0, ErrSyntax
 	}
 
 	// Pick off leading sign.
-	s0 := s
 	neg := false
 	switch s[0] {
 	case '+':
@@ -215,9 +190,7 @@ func ParseInt(s string, base int, bitSize int) (i int64, err error) {
 	// Convert unsigned and check range.
 	var un uint64
 	un, err = ParseUint(s, base, bitSize)
-	if err != nil && err.(*NumError).Err != ErrRange {
-		err.(*NumError).Func = fnParseInt
-		err.(*NumError).Num = stringslite.Clone(s0)
+	if err != nil && err != ErrRange {
 		return 0, err
 	}
 
@@ -227,10 +200,10 @@ func ParseInt(s string, base int, bitSize int) (i int64, err error) {
 
 	cutoff := uint64(1 << uint(bitSize-1))
 	if !neg && un >= cutoff {
-		return int64(cutoff - 1), rangeError(fnParseInt, s0)
+		return int64(cutoff - 1), ErrRange
 	}
 	if neg && un > cutoff {
-		return -int64(cutoff), rangeError(fnParseInt, s0)
+		return -int64(cutoff), ErrRange
 	}
 	n := int64(un)
 	if neg {
@@ -251,7 +224,7 @@ func Atoi(s string) (int, error) {
 		if s[0] == '-' || s[0] == '+' {
 			s = s[1:]
 			if len(s) < 1 {
-				return 0, syntaxError(fnAtoi, s0)
+				return 0, ErrSyntax
 			}
 		}
 
@@ -259,7 +232,7 @@ func Atoi(s string) (int, error) {
 		for _, ch := range []byte(s) {
 			ch -= '0'
 			if ch > 9 {
-				return 0, syntaxError(fnAtoi, s0)
+				return 0, ErrSyntax
 			}
 			n = n*10 + int(ch)
 		}
@@ -271,9 +244,6 @@ func Atoi(s string) (int, error) {
 
 	// Slow path for invalid, big, or underscored integers.
 	i64, err := ParseInt(s, 10, 0)
-	if nerr, ok := err.(*NumError); ok {
-		nerr.Func = fnAtoi
-	}
 	return int(i64), err
 }
 
diff --git a/src/strconv/atoi_test.go b/src/internal/strconv/atoi_test.go
index ada175200c..e8f123ea5e 100644
--- a/src/strconv/atoi_test.go
+++ b/src/internal/strconv/atoi_test.go
@@ -5,10 +5,9 @@
 package strconv_test
 
 import (
-	"errors"
 	"fmt"
 	"reflect"
-	. "strconv"
+	. "internal/strconv"
 	"testing"
 )
 
@@ -316,47 +315,6 @@ var numErrorTests = []numErrorTest{
 	{"1\x00.2", `strconv.ParseFloat: parsing "1\x00.2": failed`},
 }
 
-func init() {
-	// The parse routines return NumErrors wrapping
-	// the error and the string. Convert the tables above.
-	for i := range parseUint64Tests {
-		test := &parseUint64Tests[i]
-		if test.err != nil {
-			test.err = &NumError{"ParseUint", test.in, test.err}
-		}
-	}
-	for i := range parseUint64BaseTests {
-		test := &parseUint64BaseTests[i]
-		if test.err != nil {
-			test.err = &NumError{"ParseUint", test.in, test.err}
-		}
-	}
-	for i := range parseInt64Tests {
-		test := &parseInt64Tests[i]
-		if test.err != nil {
-			test.err = &NumError{"ParseInt", test.in, test.err}
-		}
-	}
-	for i := range parseInt64BaseTests {
-		test := &parseInt64BaseTests[i]
-		if test.err != nil {
-			test.err = &NumError{"ParseInt", test.in, test.err}
-		}
-	}
-	for i := range parseUint32Tests {
-		test := &parseUint32Tests[i]
-		if test.err != nil {
-			test.err = &NumError{"ParseUint", test.in, test.err}
-		}
-	}
-	for i := range parseInt32Tests {
-		test := &parseInt32Tests[i]
-		if test.err != nil {
-			test.err = &NumError{"ParseInt", test.in, test.err}
-		}
-	}
-}
-
 func TestParseUint32(t *testing.T) {
 	for i := range parseUint32Tests {
 		test := &parseUint32Tests[i]
@@ -475,62 +433,40 @@ func TestAtoi(t *testing.T) {
 		for i := range parseInt32Tests {
 			test := &parseInt32Tests[i]
 			out, err := Atoi(test.in)
-			var testErr error
-			if test.err != nil {
-				testErr = &NumError{"Atoi", test.in, test.err.(*NumError).Err}
-			}
-			if int(test.out) != out || !reflect.DeepEqual(testErr, err) {
-				t.Errorf("Atoi(%q) = %v, %v want %v, %v",
-					test.in, out, err, test.out, testErr)
+			if out !=int(test.out) || err != test.err {
+				t.Errorf("Atoi(%q) = %v, %v, want %v, %v", test.in, out, err, test.out, test.err)
 			}
 		}
 	case 64:
 		for i := range parseInt64Tests {
 			test := &parseInt64Tests[i]
 			out, err := Atoi(test.in)
-			var testErr error
-			if test.err != nil {
-				testErr = &NumError{"Atoi", test.in, test.err.(*NumError).Err}
-			}
-			if test.out != int64(out) || !reflect.DeepEqual(testErr, err) {
-				t.Errorf("Atoi(%q) = %v, %v want %v, %v",
-					test.in, out, err, test.out, testErr)
+			if int64(out) != test.out || err != test.err {
+				t.Errorf("Atoi(%q) = %v, %v, want %v, %v", test.in, out, err, test.out, test.err)
 			}
 		}
 	}
 }
 
-func bitSizeErrStub(name string, bitSize int) error {
-	return bitSizeError(name, "0", bitSize)
-}
-
-func baseErrStub(name string, base int) error {
-	return baseError(name, "0", base)
-}
-
-func noErrStub(name string, arg int) error {
-	return nil
-}
-
 type parseErrorTest struct {
 	arg     int
-	errStub func(name string, arg int) error
+	err error
 }
 
 var parseBitSizeTests = []parseErrorTest{
-	{-1, bitSizeErrStub},
-	{0, noErrStub},
-	{64, noErrStub},
-	{65, bitSizeErrStub},
+	{-1, ErrBitSize},
+	{0, nil},
+	{64, nil},
+	{65, ErrBitSize},
 }
 
 var parseBaseTests = []parseErrorTest{
-	{-1, baseErrStub},
-	{0, noErrStub},
-	{1, baseErrStub},
-	{2, noErrStub},
-	{36, noErrStub},
-	{37, baseErrStub},
+	{-1, ErrBase},
+	{0, nil},
+	{1, ErrBase},
+	{2, nil},
+	{36, nil},
+	{37, ErrBase},
 }
 
 func equalError(a, b error) bool {
@@ -546,11 +482,10 @@ func equalError(a, b error) bool {
 func TestParseIntBitSize(t *testing.T) {
 	for i := range parseBitSizeTests {
 		test := &parseBitSizeTests[i]
-		testErr := test.errStub("ParseInt", test.arg)
 		_, err := ParseInt("0", 0, test.arg)
-		if !equalError(testErr, err) {
+		if err != test.err {
 			t.Errorf("ParseInt(\"0\", 0, %v) = 0, %v want 0, %v",
-				test.arg, err, testErr)
+				test.arg, err, test.err)
 		}
 	}
 }
@@ -558,11 +493,10 @@ func TestParseIntBitSize(t *testing.T) {
 func TestParseUintBitSize(t *testing.T) {
 	for i := range parseBitSizeTests {
 		test := &parseBitSizeTests[i]
-		testErr := test.errStub("ParseUint", test.arg)
 		_, err := ParseUint("0", 0, test.arg)
-		if !equalError(testErr, err) {
+		if err != test.err {
 			t.Errorf("ParseUint(\"0\", 0, %v) = 0, %v want 0, %v",
-				test.arg, err, testErr)
+				test.arg, err, test.err)
 		}
 	}
 }
@@ -570,11 +504,10 @@ func TestParseUintBitSize(t *testing.T) {
 func TestParseIntBase(t *testing.T) {
 	for i := range parseBaseTests {
 		test := &parseBaseTests[i]
-		testErr := test.errStub("ParseInt", test.arg)
 		_, err := ParseInt("0", test.arg, 0)
-		if !equalError(testErr, err) {
+		if err != test.err {
 			t.Errorf("ParseInt(\"0\", %v, 0) = 0, %v want 0, %v",
-				test.arg, err, testErr)
+				test.arg, err, test.err)
 		}
 	}
 }
@@ -582,35 +515,14 @@ func TestParseIntBase(t *testing.T) {
 func TestParseUintBase(t *testing.T) {
 	for i := range parseBaseTests {
 		test := &parseBaseTests[i]
-		testErr := test.errStub("ParseUint", test.arg)
 		_, err := ParseUint("0", test.arg, 0)
-		if !equalError(testErr, err) {
+		if err != test.err {
 			t.Errorf("ParseUint(\"0\", %v, 0) = 0, %v want 0, %v",
-				test.arg, err, testErr)
-		}
-	}
-}
-
-func TestNumError(t *testing.T) {
-	for _, test := range numErrorTests {
-		err := &NumError{
-			Func: "ParseFloat",
-			Num:  test.num,
-			Err:  errors.New("failed"),
-		}
-		if got := err.Error(); got != test.want {
-			t.Errorf(`(&NumError{"ParseFloat", %q, "failed"}).Error() = %v, want %v`, test.num, got, test.want)
+				test.arg, err, test.err)
 		}
 	}
 }
 
-func TestNumErrorUnwrap(t *testing.T) {
-	err := &NumError{Err: ErrSyntax}
-	if !errors.Is(err, ErrSyntax) {
-		t.Error("errors.Is failed, wanted success")
-	}
-}
-
 func BenchmarkParseInt(b *testing.B) {
 	b.Run("Pos", func(b *testing.B) {
 		benchmarkParseInt(b, 1)
diff --git a/src/strconv/ctoa.go b/src/internal/strconv/ctoa.go
index fd7f941d70..fd7f941d70 100644
--- a/src/strconv/ctoa.go
+++ b/src/internal/strconv/ctoa.go
diff --git a/src/strconv/ctoa_test.go b/src/internal/strconv/ctoa_test.go
index 8b77898ecc..c24f30272a 100644
--- a/src/strconv/ctoa_test.go
+++ b/src/internal/strconv/ctoa_test.go
@@ -5,7 +5,7 @@
 package strconv_test
 
 import (
-	. "strconv"
+	. "internal/strconv"
 	"testing"
 )
 
diff --git a/src/strconv/decimal.go b/src/internal/strconv/decimal.go
index b58001888e..b58001888e 100644
--- a/src/strconv/decimal.go
+++ b/src/internal/strconv/decimal.go
diff --git a/src/strconv/decimal_test.go b/src/internal/strconv/decimal_test.go
index 13a127f5b2..a60096e1c8 100644
--- a/src/strconv/decimal_test.go
+++ b/src/internal/strconv/decimal_test.go
@@ -5,7 +5,7 @@
 package strconv_test
 
 import (
-	. "strconv"
+	. "internal/strconv"
 	"testing"
 )
 
diff --git a/src/internal/strconv/deps.go b/src/internal/strconv/deps.go
new file mode 100644
index 0000000000..04331130c2
--- /dev/null
+++ b/src/internal/strconv/deps.go
@@ -0,0 +1,30 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strconv
+
+import "unsafe"
+
+// Implementations to avoid importing other dependencies.
+
+// package math
+
+func float64frombits(b uint64) float64 { return *(*float64)(unsafe.Pointer(&b)) }
+func float32frombits(b uint32) float32 { return *(*float32)(unsafe.Pointer(&b)) }
+func float64bits(f float64) uint64     { return *(*uint64)(unsafe.Pointer(&f)) }
+func float32bits(f float32) uint32     { return *(*uint32)(unsafe.Pointer(&f)) }
+
+func inf(sign int) float64 {
+	var v uint64
+	if sign >= 0 {
+		v = 0x7FF0000000000000
+	} else {
+		v = 0xFFF0000000000000
+	}
+	return float64frombits(v)
+}
+
+func isNaN(f float64) (is bool) { return f != f }
+
+func nan() float64 { return float64frombits(0x7FF8000000000001) }
diff --git a/src/internal/strconv/export_test.go b/src/internal/strconv/export_test.go
new file mode 100644
index 0000000000..bea741e6fb
--- /dev/null
+++ b/src/internal/strconv/export_test.go
@@ -0,0 +1,28 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strconv
+
+type Uint128 = uint128
+
+var (
+	MulLog10_2       = mulLog10_2
+	MulLog2_10       = mulLog2_10
+	ParseFloatPrefix = parseFloatPrefix
+	Pow10            = pow10
+	Umul128          = umul128
+	Umul192          = umul192
+)
+
+func NewDecimal(i uint64) *decimal {
+	d := new(decimal)
+	d.Assign(i)
+	return d
+}
+
+func SetOptimize(b bool) bool {
+	old := optimize
+	optimize = b
+	return old
+}
diff --git a/src/strconv/fp_test.go b/src/internal/strconv/fp_test.go
index 376e8f591c..042328c7d4 100644
--- a/src/strconv/fp_test.go
+++ b/src/internal/strconv/fp_test.go
@@ -8,7 +8,7 @@ import (
 	"bufio"
 	_ "embed"
 	"fmt"
-	"strconv"
+	"internal/strconv"
 	"strings"
 	"testing"
 )
diff --git a/src/strconv/ftoa.go b/src/internal/strconv/ftoa.go
index 1d4bf770be..1aec5447ec 100644
--- a/src/strconv/ftoa.go
+++ b/src/internal/strconv/ftoa.go
@@ -10,7 +10,10 @@
 
 package strconv
 
-import "math"
+const (
+	lowerhex = "0123456789abcdef"
+	upperhex = "0123456789ABCDEF"
+)
 
 type floatInfo struct {
 	mantbits uint
@@ -71,10 +74,10 @@ func genericFtoa(dst []byte, val float64, fmt byte, prec, bitSize int) []byte {
 	var flt *floatInfo
 	switch bitSize {
 	case 32:
-		bits = uint64(math.Float32bits(float32(val)))
+		bits = uint64(float32bits(float32(val)))
 		flt = &float32info
 	case 64:
-		bits = math.Float64bits(val)
+		bits = float64bits(val)
 		flt = &float64info
 	default:
 		panic("strconv: illegal AppendFloat/FormatFloat bitSize")
diff --git a/src/strconv/ftoa_test.go b/src/internal/strconv/ftoa_test.go
index 40faa433a6..14d1200ff2 100644
--- a/src/strconv/ftoa_test.go
+++ b/src/internal/strconv/ftoa_test.go
@@ -7,7 +7,7 @@ package strconv_test
 import (
 	"math"
 	"math/rand"
-	. "strconv"
+	. "internal/strconv"
 	"testing"
 )
 
diff --git a/src/strconv/ftoaryu.go b/src/internal/strconv/ftoaryu.go
index 9349df955f..9349df955f 100644
--- a/src/strconv/ftoaryu.go
+++ b/src/internal/strconv/ftoaryu.go
diff --git a/src/internal/strconv/import_test.go b/src/internal/strconv/import_test.go
new file mode 100644
index 0000000000..0cbc451651
--- /dev/null
+++ b/src/internal/strconv/import_test.go
@@ -0,0 +1,18 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strconv_test
+
+import . "internal/strconv"
+
+type uint128 = Uint128
+
+var (
+	mulLog10_2       = MulLog10_2
+	mulLog2_10       = MulLog2_10
+	parseFloatPrefix = ParseFloatPrefix
+	pow10            = Pow10
+	umul128          = Umul128
+	umul192          = Umul192
+)
diff --git a/src/strconv/itoa.go b/src/internal/strconv/itoa.go
index 7884e8e987..d4ca478eb0 100644
--- a/src/strconv/itoa.go
+++ b/src/internal/strconv/itoa.go
@@ -5,8 +5,8 @@
 package strconv
 
 import (
+	"internal/goarch"
 	"math/bits"
-	"runtime"
 )
 
 // FormatUint returns the string representation of i in the given base,
@@ -200,7 +200,7 @@ func formatBase10(a []byte, u uint64) int {
 		// or can split the uint64 into uint32-sized chunks.
 		// On most systems, the uint32 math is faster, but not all.
 		// The decision here is based on benchmarking.
-		itoaPure64 = host64bit && runtime.GOARCH != "amd64" && runtime.GOARCH != "arm64" && runtime.GOARCH != "s390x"
+		itoaPure64 = host64bit && goarch.GOARCH != "amd64" && goarch.GOARCH != "arm64" && goarch.GOARCH != "s390x"
 
 		// 64-bit systems can all use 64-bit div and mod by a constant,
 		// which the compiler rewrites to use 64x64→128-bit multiplies.
diff --git a/src/strconv/itoa_test.go b/src/internal/strconv/itoa_test.go
index 9dbf812d4b..1629e45d48 100644
--- a/src/strconv/itoa_test.go
+++ b/src/internal/strconv/itoa_test.go
@@ -6,7 +6,7 @@ package strconv_test
 
 import (
 	"fmt"
-	. "strconv"
+	. "internal/strconv"
 	"testing"
 )
 
diff --git a/src/strconv/math.go b/src/internal/strconv/math.go
index f0f3d5fe54..f0f3d5fe54 100644
--- a/src/strconv/math.go
+++ b/src/internal/strconv/math.go
diff --git a/src/strconv/math_test.go b/src/internal/strconv/math_test.go
index 19b7ea6c75..d4f881b5e7 100644
--- a/src/strconv/math_test.go
+++ b/src/internal/strconv/math_test.go
@@ -6,7 +6,7 @@ package strconv_test
 
 import (
 	"math"
-	. "strconv"
+	. "internal/strconv"
 	"testing"
 )
 
diff --git a/src/strconv/pow10gen.go b/src/internal/strconv/pow10gen.go
index 2d428fe088..2d428fe088 100644
--- a/src/strconv/pow10gen.go
+++ b/src/internal/strconv/pow10gen.go
diff --git a/src/strconv/pow10tab.go b/src/internal/strconv/pow10tab.go
index 029ae02b66..029ae02b66 100644
--- a/src/strconv/pow10tab.go
+++ b/src/internal/strconv/pow10tab.go
diff --git a/src/strconv/testdata/testfp.txt b/src/internal/strconv/testdata/testfp.txt
index 08d3c4ef09..08d3c4ef09 100644
--- a/src/strconv/testdata/testfp.txt
+++ b/src/internal/strconv/testdata/testfp.txt
diff --git a/src/strconv/export_test.go b/src/strconv/export_test.go
index 3518bb233c..7a3c761e68 100644
--- a/src/strconv/export_test.go
+++ b/src/strconv/export_test.go
@@ -4,27 +4,7 @@
 
 package strconv
 
-type Uint128 = uint128
-
 var (
-	BaseError        = baseError
-	BitSizeError     = bitSizeError
-	MulLog10_2       = mulLog10_2
-	MulLog2_10       = mulLog2_10
-	ParseFloatPrefix = parseFloatPrefix
-	Pow10            = pow10
-	Umul128          = umul128
-	Umul192          = umul192
+	BaseError    = baseError
+	BitSizeError = bitSizeError
 )
-
-func NewDecimal(i uint64) *decimal {
-	d := new(decimal)
-	d.Assign(i)
-	return d
-}
-
-func SetOptimize(b bool) bool {
-	old := optimize
-	optimize = b
-	return old
-}
diff --git a/src/strconv/import_test.go b/src/strconv/import_test.go
index 05d957a623..b44678bc7c 100644
--- a/src/strconv/import_test.go
+++ b/src/strconv/import_test.go
@@ -6,15 +6,7 @@ package strconv_test
 
 import . "strconv"
 
-type uint128 = Uint128
-
 var (
-	baseError        = BaseError
-	bitSizeError     = BitSizeError
-	mulLog10_2       = MulLog10_2
-	mulLog2_10       = MulLog2_10
-	parseFloatPrefix = ParseFloatPrefix
-	pow10            = Pow10
-	umul128          = Umul128
-	umul192          = Umul192
+	baseError    = BaseError
+	bitSizeError = BitSizeError
 )
diff --git a/src/strconv/number.go b/src/strconv/number.go
new file mode 100644
index 0000000000..3fa625c35f
--- /dev/null
+++ b/src/strconv/number.go
@@ -0,0 +1,286 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strconv
+
+import (
+	"errors"
+	"internal/strconv"
+	"internal/stringslite"
+)
+
+// IntSize is the size in bits of an int or uint value.
+const IntSize = strconv.IntSize
+
+// ParseBool returns the boolean value represented by the string.
+// It accepts 1, t, T, TRUE, true, True, 0, f, F, FALSE, false, False.
+// Any other value returns an error.
+func ParseBool(str string) (bool, error) {
+	x, err := strconv.ParseBool(str)
+	if err != nil {
+		return x, toError("ParseBool", str, 0, 0, err)
+	}
+	return x, nil
+}
+
+// FormatBool returns "true" or "false" according to the value of b.
+func FormatBool(b bool) string {
+	return strconv.FormatBool(b)
+}
+
+// AppendBool appends "true" or "false", according to the value of b,
+// to dst and returns the extended buffer.
+func AppendBool(dst []byte, b bool) []byte {
+	return strconv.AppendBool(dst, b)
+}
+
+// ParseComplex converts the string s to a complex number
+// with the precision specified by bitSize: 64 for complex64, or 128 for complex128.
+// When bitSize=64, the result still has type complex128, but it will be
+// convertible to complex64 without changing its value.
+//
+// The number represented by s must be of the form N, Ni, or N±Ni, where N stands
+// for a floating-point number as recognized by [ParseFloat], and i is the imaginary
+// component. If the second N is unsigned, a + sign is required between the two components
+// as indicated by the ±. If the second N is NaN, only a + sign is accepted.
+// The form may be parenthesized and cannot contain any spaces.
+// The resulting complex number consists of the two components converted by ParseFloat.
+//
+// The errors that ParseComplex returns have concrete type [*NumError]
+// and include err.Num = s.
+//
+// If s is not syntactically well-formed, ParseComplex returns err.Err = ErrSyntax.
+//
+// If s is syntactically well-formed but either component is more than 1/2 ULP
+// away from the largest floating point number of the given component's size,
+// ParseComplex returns err.Err = ErrRange and c = ±Inf for the respective component.
+func ParseComplex(s string, bitSize int) (complex128, error) {
+	x, err := strconv.ParseComplex(s, bitSize)
+	if err != nil {
+		return x, toError("ParseComplex", s, 0, bitSize, err)
+	}
+	return x, nil
+}
+
+// ParseFloat converts the string s to a floating-point number
+// with the precision specified by bitSize: 32 for float32, or 64 for float64.
+// When bitSize=32, the result still has type float64, but it will be
+// convertible to float32 without changing its value.
+//
+// ParseFloat accepts decimal and hexadecimal floating-point numbers
+// as defined by the Go syntax for [floating-point literals].
+// If s is well-formed and near a valid floating-point number,
+// ParseFloat returns the nearest floating-point number rounded
+// using IEEE754 unbiased rounding.
+// (Parsing a hexadecimal floating-point value only rounds when
+// there are more bits in the hexadecimal representation than
+// will fit in the mantissa.)
+//
+// The errors that ParseFloat returns have concrete type *NumError
+// and include err.Num = s.
+//
+// If s is not syntactically well-formed, ParseFloat returns err.Err = ErrSyntax.
+//
+// If s is syntactically well-formed but is more than 1/2 ULP
+// away from the largest floating point number of the given size,
+// ParseFloat returns f = ±Inf, err.Err = ErrRange.
+//
+// ParseFloat recognizes the string "NaN", and the (possibly signed) strings "Inf" and "Infinity"
+// as their respective special floating point values. It ignores case when matching.
+//
+// [floating-point literals]: https://go.dev/ref/spec#Floating-point_literals
+func ParseFloat(s string, bitSize int) (float64, error) {
+	x, err := strconv.ParseFloat(s, bitSize)
+	if err != nil {
+		return x, toError("ParseFloat", s, 0, bitSize, err)
+	}
+	return x, nil
+}
+
+// ParseUint is like [ParseInt] but for unsigned numbers.
+//
+// A sign prefix is not permitted.
+func ParseUint(s string, base int, bitSize int) (uint64, error) {
+	x, err := strconv.ParseUint(s, base, bitSize)
+	if err != nil {
+		return x, toError("ParseUint", s, base, bitSize, err)
+	}
+	return x, nil
+}
+
+// ParseInt interprets a string s in the given base (0, 2 to 36) and
+// bit size (0 to 64) and returns the corresponding value i.
+//
+// The string may begin with a leading sign: "+" or "-".
+//
+// If the base argument is 0, the true base is implied by the string's
+// prefix following the sign (if present): 2 for "0b", 8 for "0" or "0o",
+// 16 for "0x", and 10 otherwise. Also, for argument base 0 only,
+// underscore characters are permitted as defined by the Go syntax for
+// [integer literals].
+//
+// The bitSize argument specifies the integer type
+// that the result must fit into. Bit sizes 0, 8, 16, 32, and 64
+// correspond to int, int8, int16, int32, and int64.
+// If bitSize is below 0 or above 64, an error is returned.
+//
+// The errors that ParseInt returns have concrete type [*NumError]
+// and include err.Num = s. If s is empty or contains invalid
+// digits, err.Err = [ErrSyntax] and the returned value is 0;
+// if the value corresponding to s cannot be represented by a
+// signed integer of the given size, err.Err = [ErrRange] and the
+// returned value is the maximum magnitude integer of the
+// appropriate bitSize and sign.
+//
+// [integer literals]: https://go.dev/ref/spec#Integer_literals
+func ParseInt(s string, base int, bitSize int) (i int64, err error) {
+	x, err := strconv.ParseInt(s, base, bitSize)
+	if err != nil {
+		return x, toError("ParseInt", s, base, bitSize, err)
+	}
+	return x, nil
+}
+
+// Atoi is equivalent to ParseInt(s, 10, 0), converted to type int.
+func Atoi(s string) (int, error) {
+	x, err := strconv.Atoi(s)
+	if err != nil {
+		return x, toError("Atoi", s, 0, 0, err)
+	}
+	return strconv.Atoi(s)
+}
+
+// FormatComplex converts the complex number c to a string of the
+// form (a+bi) where a and b are the real and imaginary parts,
+// formatted according to the format fmt and precision prec.
+//
+// The format fmt and precision prec have the same meaning as in [FormatFloat].
+// It rounds the result assuming that the original was obtained from a complex
+// value of bitSize bits, which must be 64 for complex64 and 128 for complex128.
+func FormatComplex(c complex128, fmt byte, prec, bitSize int) string {
+	return strconv.FormatComplex(c, fmt, prec, bitSize)
+}
+
+// FormatFloat converts the floating-point number f to a string,
+// according to the format fmt and precision prec. It rounds the
+// result assuming that the original was obtained from a floating-point
+// value of bitSize bits (32 for float32, 64 for float64).
+//
+// The format fmt is one of
+//   - 'b' (-ddddp±ddd, a binary exponent),
+//   - 'e' (-d.dddde±dd, a decimal exponent),
+//   - 'E' (-d.ddddE±dd, a decimal exponent),
+//   - 'f' (-ddd.dddd, no exponent),
+//   - 'g' ('e' for large exponents, 'f' otherwise),
+//   - 'G' ('E' for large exponents, 'f' otherwise),
+//   - 'x' (-0xd.ddddp±ddd, a hexadecimal fraction and binary exponent), or
+//   - 'X' (-0Xd.ddddP±ddd, a hexadecimal fraction and binary exponent).
+//
+// The precision prec controls the number of digits (excluding the exponent)
+// printed by the 'e', 'E', 'f', 'g', 'G', 'x', and 'X' formats.
+// For 'e', 'E', 'f', 'x', and 'X', it is the number of digits after the decimal point.
+// For 'g' and 'G' it is the maximum number of significant digits (trailing
+// zeros are removed).
+// The special precision -1 uses the smallest number of digits
+// necessary such that ParseFloat will return f exactly.
+// The exponent is written as a decimal integer;
+// for all formats other than 'b', it will be at least two digits.
+func FormatFloat(f float64, fmt byte, prec, bitSize int) string {
+	return strconv.FormatFloat(f, fmt, prec, bitSize)
+}
+
+// AppendFloat appends the string form of the floating-point number f,
+// as generated by [FormatFloat], to dst and returns the extended buffer.
+func AppendFloat(dst []byte, f float64, fmt byte, prec, bitSize int) []byte {
+	return strconv.AppendFloat(dst, f, fmt, prec, bitSize)
+}
+
+// FormatUint returns the string representation of i in the given base,
+// for 2 <= base <= 36. The result uses the lower-case letters 'a' to 'z'
+// for digit values >= 10.
+func FormatUint(i uint64, base int) string {
+	return strconv.FormatUint(i, base)
+}
+
+// FormatInt returns the string representation of i in the given base,
+// for 2 <= base <= 36. The result uses the lower-case letters 'a' to 'z'
+// for digit values >= 10.
+func FormatInt(i int64, base int) string {
+	return strconv.FormatInt(i, base)
+}
+
+// Itoa is equivalent to [FormatInt](int64(i), 10).
+func Itoa(i int) string {
+	return strconv.Itoa(i)
+}
+
+// AppendInt appends the string form of the integer i,
+// as generated by [FormatInt], to dst and returns the extended buffer.
+func AppendInt(dst []byte, i int64, base int) []byte {
+	return strconv.AppendInt(dst, i, base)
+}
+
+// AppendUint appends the string form of the unsigned integer i,
+// as generated by [FormatUint], to dst and returns the extended buffer.
+func AppendUint(dst []byte, i uint64, base int) []byte {
+	return strconv.AppendUint(dst, i, base)
+}
+
+// toError converts from internal/strconv.Error to the error guaranteed by this package's APIs.
+func toError(fn, s string, base, bitSize int, err error) error {
+	switch err {
+	case strconv.ErrSyntax:
+		return syntaxError(fn, s)
+	case strconv.ErrRange:
+		return rangeError(fn, s)
+	case strconv.ErrBase:
+		return baseError(fn, s, base)
+	case strconv.ErrBitSize:
+		return bitSizeError(fn, s, bitSize)
+	}
+	return err
+}
+
+// ErrRange indicates that a value is out of range for the target type.
+var ErrRange = errors.New("value out of range")
+
+// ErrSyntax indicates that a value does not have the right syntax for the target type.
+var ErrSyntax = errors.New("invalid syntax")
+
+// A NumError records a failed conversion.
+type NumError struct {
+	Func string // the failing function (ParseBool, ParseInt, ParseUint, ParseFloat, ParseComplex)
+	Num  string // the input
+	Err  error  // the reason the conversion failed (e.g. ErrRange, ErrSyntax, etc.)
+}
+
+func (e *NumError) Error() string {
+	return "strconv." + e.Func + ": " + "parsing " + Quote(e.Num) + ": " + e.Err.Error()
+}
+
+func (e *NumError) Unwrap() error { return e.Err }
+
+// All ParseXXX functions allow the input string to escape to the error value.
+// This hurts strconv.ParseXXX(string(b)) calls where b is []byte since
+// the conversion from []byte must allocate a string on the heap.
+// If we assume errors are infrequent, then we can avoid escaping the input
+// back to the output by copying it first. This allows the compiler to call
+// strconv.ParseXXX without a heap allocation for most []byte to string
+// conversions, since it can now prove that the string cannot escape Parse.
+
+func syntaxError(fn, str string) *NumError {
+	return &NumError{fn, stringslite.Clone(str), ErrSyntax}
+}
+
+func rangeError(fn, str string) *NumError {
+	return &NumError{fn, stringslite.Clone(str), ErrRange}
+}
+
+func baseError(fn, str string, base int) *NumError {
+	return &NumError{fn, stringslite.Clone(str), errors.New("invalid base " + Itoa(base))}
+}
+
+func bitSizeError(fn, str string, bitSize int) *NumError {
+	return &NumError{fn, stringslite.Clone(str), errors.New("invalid bit size " + Itoa(bitSize))}
+}
diff --git a/src/strconv/number_test.go b/src/strconv/number_test.go
new file mode 100644
index 0000000000..4408bc0556
--- /dev/null
+++ b/src/strconv/number_test.go
@@ -0,0 +1,956 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Note: These tests are focused mainly on generating the right errors.
+// The extensive numerical tests are in ../internal/strconv.
+// Add new tests there instead of here whenever possible.
+
+package strconv_test
+
+import (
+	"bytes"
+	"errors"
+	"math"
+	"math/cmplx"
+	"reflect"
+	. "strconv"
+	"testing"
+)
+
+type atobTest struct {
+	in  string
+	out bool
+	err error
+}
+
+var atobtests = []atobTest{
+	{"", false, ErrSyntax},
+	{"asdf", false, ErrSyntax},
+	{"0", false, nil},
+	{"false", false, nil},
+	{"true", true, nil},
+}
+
+func TestParseBool(t *testing.T) {
+	for _, test := range atobtests {
+		b, e := ParseBool(test.in)
+		if test.err != nil {
+			// expect an error
+			if e == nil {
+				t.Errorf("ParseBool(%s) = nil; want %s", test.in, test.err)
+			} else {
+				// NumError assertion must succeed; it's the only thing we return.
+				if e.(*NumError).Err != test.err {
+					t.Errorf("ParseBool(%s) = %s; want %s", test.in, e, test.err)
+				}
+			}
+		} else {
+			if e != nil {
+				t.Errorf("ParseBool(%s) = %s; want nil", test.in, e)
+			}
+			if b != test.out {
+				t.Errorf("ParseBool(%s) = %t; want %t", test.in, b, test.out)
+			}
+		}
+	}
+}
+
+var boolString = map[bool]string{
+	true:  "true",
+	false: "false",
+}
+
+func TestFormatBool(t *testing.T) {
+	for b, s := range boolString {
+		if f := FormatBool(b); f != s {
+			t.Errorf("FormatBool(%v) = %q; want %q", b, f, s)
+		}
+	}
+}
+
+type appendBoolTest struct {
+	b   bool
+	in  []byte
+	out []byte
+}
+
+var appendBoolTests = []appendBoolTest{
+	{true, []byte("foo "), []byte("foo true")},
+	{false, []byte("foo "), []byte("foo false")},
+}
+
+func TestAppendBool(t *testing.T) {
+	for _, test := range appendBoolTests {
+		b := AppendBool(test.in, test.b)
+		if !bytes.Equal(b, test.out) {
+			t.Errorf("AppendBool(%q, %v) = %q; want %q", test.in, test.b, b, test.out)
+		}
+	}
+}
+
+var (
+	infp0 = complex(math.Inf(+1), 0)
+	infm0 = complex(math.Inf(-1), 0)
+	inf0p = complex(0, math.Inf(+1))
+	inf0m = complex(0, math.Inf(-1))
+
+	infpp = complex(math.Inf(+1), math.Inf(+1))
+	infpm = complex(math.Inf(+1), math.Inf(-1))
+	infmp = complex(math.Inf(-1), math.Inf(+1))
+	infmm = complex(math.Inf(-1), math.Inf(-1))
+)
+
+type atocTest struct {
+	in  string
+	out complex128
+	err error
+}
+
+func TestParseComplex(t *testing.T) {
+	tests := []atocTest{
+		// Clearly invalid
+		{"", 0, ErrSyntax},
+		{" ", 0, ErrSyntax},
+		{"(", 0, ErrSyntax},
+		{")", 0, ErrSyntax},
+		{"i", 0, ErrSyntax},
+		{"+i", 0, ErrSyntax},
+		{"-i", 0, ErrSyntax},
+		{"1I", 0, ErrSyntax},
+		{"10  + 5i", 0, ErrSyntax},
+		{"3+", 0, ErrSyntax},
+		{"3+5", 0, ErrSyntax},
+		{"3+5+5i", 0, ErrSyntax},
+
+		// Parentheses
+		{"()", 0, ErrSyntax},
+		{"(i)", 0, ErrSyntax},
+		{"(0)", 0, nil},
+		{"(1i)", 1i, nil},
+		{"(3.0+5.5i)", 3.0 + 5.5i, nil},
+		{"(1)+1i", 0, ErrSyntax},
+		{"(3.0+5.5i", 0, ErrSyntax},
+		{"3.0+5.5i)", 0, ErrSyntax},
+
+		// NaNs
+		{"NaN", complex(math.NaN(), 0), nil},
+		{"NANi", complex(0, math.NaN()), nil},
+		{"nan+nAni", complex(math.NaN(), math.NaN()), nil},
+		{"+NaN", 0, ErrSyntax},
+		{"-NaN", 0, ErrSyntax},
+		{"NaN-NaNi", 0, ErrSyntax},
+
+		// Infs
+		{"Inf", infp0, nil},
+		{"+inf", infp0, nil},
+		{"-inf", infm0, nil},
+		{"Infinity", infp0, nil},
+		{"+INFINITY", infp0, nil},
+		{"-infinity", infm0, nil},
+		{"+infi", inf0p, nil},
+		{"0-infinityi", inf0m, nil},
+		{"Inf+Infi", infpp, nil},
+		{"+Inf-Infi", infpm, nil},
+		{"-Infinity+Infi", infmp, nil},
+		{"inf-inf", 0, ErrSyntax},
+
+		// Zeros
+		{"0", 0, nil},
+		{"0i", 0, nil},
+		{"-0.0i", 0, nil},
+		{"0+0.0i", 0, nil},
+		{"0e+0i", 0, nil},
+		{"0e-0+0i", 0, nil},
+		{"-0.0-0.0i", 0, nil},
+		{"0e+012345", 0, nil},
+		{"0x0p+012345i", 0, nil},
+		{"0x0.00p-012345i", 0, nil},
+		{"+0e-0+0e-0i", 0, nil},
+		{"0e+0+0e+0i", 0, nil},
+		{"-0e+0-0e+0i", 0, nil},
+
+		// Regular non-zeroes
+		{"0.1", 0.1, nil},
+		{"0.1i", 0 + 0.1i, nil},
+		{"0.123", 0.123, nil},
+		{"0.123i", 0 + 0.123i, nil},
+		{"0.123+0.123i", 0.123 + 0.123i, nil},
+		{"99", 99, nil},
+		{"+99", 99, nil},
+		{"-99", -99, nil},
+		{"+1i", 1i, nil},
+		{"-1i", -1i, nil},
+		{"+3+1i", 3 + 1i, nil},
+		{"30+3i", 30 + 3i, nil},
+		{"+3e+3-3e+3i", 3e+3 - 3e+3i, nil},
+		{"+3e+3+3e+3i", 3e+3 + 3e+3i, nil},
+		{"+3e+3+3e+3i+", 0, ErrSyntax},
+
+		// Separators
+		{"0.1", 0.1, nil},
+		{"0.1i", 0 + 0.1i, nil},
+		{"0.1_2_3", 0.123, nil},
+		{"+0x_3p3i", 0x3p3i, nil},
+		{"0_0+0x_0p0i", 0, nil},
+		{"0x_10.3p-8+0x3p3i", 0x10.3p-8 + 0x3p3i, nil},
+		{"+0x_1_0.3p-8+0x_3_0p3i", 0x10.3p-8 + 0x30p3i, nil},
+		{"0x1_0.3p+8-0x_3p3i", 0x10.3p+8 - 0x3p3i, nil},
+
+		// Hexadecimals
+		{"0x10.3p-8+0x3p3i", 0x10.3p-8 + 0x3p3i, nil},
+		{"+0x10.3p-8+0x3p3i", 0x10.3p-8 + 0x3p3i, nil},
+		{"0x10.3p+8-0x3p3i", 0x10.3p+8 - 0x3p3i, nil},
+		{"0x1p0", 1, nil},
+		{"0x1p1", 2, nil},
+		{"0x1p-1", 0.5, nil},
+		{"0x1ep-1", 15, nil},
+		{"-0x1ep-1", -15, nil},
+		{"-0x2p3", -16, nil},
+		{"0x1e2", 0, ErrSyntax},
+		{"1p2", 0, ErrSyntax},
+		{"0x1e2i", 0, ErrSyntax},
+
+		// ErrRange
+		// next float64 - too large
+		{"+0x1p1024", infp0, ErrRange},
+		{"-0x1p1024", infm0, ErrRange},
+		{"+0x1p1024i", inf0p, ErrRange},
+		{"-0x1p1024i", inf0m, ErrRange},
+		{"+0x1p1024+0x1p1024i", infpp, ErrRange},
+		{"+0x1p1024-0x1p1024i", infpm, ErrRange},
+		{"-0x1p1024+0x1p1024i", infmp, ErrRange},
+		{"-0x1p1024-0x1p1024i", infmm, ErrRange},
+		// the border is ...158079
+		// borderline - okay
+		{"+0x1.fffffffffffff7fffp1023+0x1.fffffffffffff7fffp1023i", 1.7976931348623157e+308 + 1.7976931348623157e+308i, nil},
+		{"+0x1.fffffffffffff7fffp1023-0x1.fffffffffffff7fffp1023i", 1.7976931348623157e+308 - 1.7976931348623157e+308i, nil},
+		{"-0x1.fffffffffffff7fffp1023+0x1.fffffffffffff7fffp1023i", -1.7976931348623157e+308 + 1.7976931348623157e+308i, nil},
+		{"-0x1.fffffffffffff7fffp1023-0x1.fffffffffffff7fffp1023i", -1.7976931348623157e+308 - 1.7976931348623157e+308i, nil},
+		// borderline - too large
+		{"+0x1.fffffffffffff8p1023", infp0, ErrRange},
+		{"-0x1fffffffffffff.8p+971", infm0, ErrRange},
+		{"+0x1.fffffffffffff8p1023i", inf0p, ErrRange},
+		{"-0x1fffffffffffff.8p+971i", inf0m, ErrRange},
+		{"+0x1.fffffffffffff8p1023+0x1.fffffffffffff8p1023i", infpp, ErrRange},
+		{"+0x1.fffffffffffff8p1023-0x1.fffffffffffff8p1023i", infpm, ErrRange},
+		{"-0x1fffffffffffff.8p+971+0x1fffffffffffff.8p+971i", infmp, ErrRange},
+		{"-0x1fffffffffffff8p+967-0x1fffffffffffff8p+967i", infmm, ErrRange},
+		// a little too large
+		{"1e308+1e308i", 1e+308 + 1e+308i, nil},
+		{"2e308+2e308i", infpp, ErrRange},
+		{"1e309+1e309i", infpp, ErrRange},
+		{"0x1p1025+0x1p1025i", infpp, ErrRange},
+		{"2e308", infp0, ErrRange},
+		{"1e309", infp0, ErrRange},
+		{"0x1p1025", infp0, ErrRange},
+		{"2e308i", inf0p, ErrRange},
+		{"1e309i", inf0p, ErrRange},
+		{"0x1p1025i", inf0p, ErrRange},
+		// way too large
+		{"+1e310+1e310i", infpp, ErrRange},
+		{"+1e310-1e310i", infpm, ErrRange},
+		{"-1e310+1e310i", infmp, ErrRange},
+		{"-1e310-1e310i", infmm, ErrRange},
+		// under/overflow exponent
+		{"1e-4294967296", 0, nil},
+		{"1e-4294967296i", 0, nil},
+		{"1e-4294967296+1i", 1i, nil},
+		{"1+1e-4294967296i", 1, nil},
+		{"1e-4294967296+1e-4294967296i", 0, nil},
+		{"1e+4294967296", infp0, ErrRange},
+		{"1e+4294967296i", inf0p, ErrRange},
+		{"1e+4294967296+1e+4294967296i", infpp, ErrRange},
+		{"1e+4294967296-1e+4294967296i", infpm, ErrRange},
+	}
+	for i := range tests {
+		test := &tests[i]
+		if test.err != nil {
+			test.err = &NumError{Func: "ParseComplex", Num: test.in, Err: test.err}
+		}
+		got, err := ParseComplex(test.in, 128)
+		if !reflect.DeepEqual(err, test.err) {
+			t.Fatalf("ParseComplex(%q, 128) = %v, %v; want %v, %v", test.in, got, err, test.out, test.err)
+		}
+		if !(cmplx.IsNaN(test.out) && cmplx.IsNaN(got)) && got != test.out {
+			t.Fatalf("ParseComplex(%q, 128) = %v, %v; want %v, %v", test.in, got, err, test.out, test.err)
+		}
+
+		if complex128(complex64(test.out)) == test.out {
+			got, err := ParseComplex(test.in, 64)
+			if !reflect.DeepEqual(err, test.err) {
+				t.Fatalf("ParseComplex(%q, 64) = %v, %v; want %v, %v", test.in, got, err, test.out, test.err)
+			}
+			got64 := complex64(got)
+			if complex128(got64) != test.out {
+				t.Fatalf("ParseComplex(%q, 64) = %v, %v; want %v, %v", test.in, got, err, test.out, test.err)
+			}
+		}
+	}
+}
+
+// Issue 42297: allow ParseComplex(s, not_32_or_64) for legacy reasons
+func TestParseComplexIncorrectBitSize(t *testing.T) {
+	const s = "1.5e308+1.0e307i"
+	const want = 1.5e308 + 1.0e307i
+
+	for _, bitSize := range []int{0, 10, 100, 256} {
+		c, err := ParseComplex(s, bitSize)
+		if err != nil {
+			t.Fatalf("ParseComplex(%q, %d) gave error %s", s, bitSize, err)
+		}
+		if c != want {
+			t.Fatalf("ParseComplex(%q, %d) = %g (expected %g)", s, bitSize, c, want)
+		}
+	}
+}
+
+type atofTest struct {
+	in  string
+	out string
+	err error
+}
+
+var atoftests = []atofTest{
+	{"", "0", ErrSyntax},
+	{"1.25", "1.25", nil},
+	{"+1", "1", nil},
+	{"1x", "0", ErrSyntax},
+	{"1.1.", "0", ErrSyntax},
+	{"1e23", "1e+23", nil},
+	{"1E23", "1e+23", nil},
+	{"0x1fFe2.p0", "131042", nil},
+	{"0x1fFe2.P0", "131042", nil},
+	{"-0x2p3", "-16", nil},
+	{"0x0.fp4", "15", nil},
+	{"0x0.fp0", "0.9375", nil},
+	{"0x1e2", "0", ErrSyntax},
+	{"1p2", "0", ErrSyntax},
+	{"0x1p1024", "+Inf", ErrRange},
+	{"-0x1p1024", "-Inf", ErrRange},
+	{"0x1.fffffffffffff7fffp1023", "1.7976931348623157e+308", nil},
+	{"-0x1.fffffffffffff7fffp1023", "-1.7976931348623157e+308", nil},
+	{"1.797693134862315808e308", "+Inf", ErrRange},
+	{"-1.797693134862315808e308", "-Inf", ErrRange},
+}
+
+func init() {
+	// The atof routines return NumErrors wrapping
+	// the error and the string. Convert the table above.
+	for i := range atoftests {
+		test := &atoftests[i]
+		if test.err != nil {
+			test.err = &NumError{"ParseFloat", test.in, test.err}
+		}
+	}
+}
+
+func TestAtof(t *testing.T) {
+	for i := 0; i < len(atoftests); i++ {
+		test := &atoftests[i]
+		out, err := ParseFloat(test.in, 64)
+		outs := FormatFloat(out, 'g', -1, 64)
+		if outs != test.out || !reflect.DeepEqual(err, test.err) {
+			t.Errorf("ParseFloat(%v, 64) = %v, %v want %v, %v",
+				test.in, out, err, test.out, test.err)
+		}
+
+		if float64(float32(out)) == out {
+			out, err := ParseFloat(test.in, 32)
+			out32 := float32(out)
+			if float64(out32) != out {
+				t.Errorf("ParseFloat(%v, 32) = %v, not a float32 (closest is %v)", test.in, out, float64(out32))
+				continue
+			}
+			outs := FormatFloat(float64(out32), 'g', -1, 32)
+			if outs != test.out || !reflect.DeepEqual(err, test.err) {
+				t.Errorf("ParseFloat(%v, 32) = %v, %v want %v, %v  # %v",
+					test.in, out32, err, test.out, test.err, out)
+			}
+		}
+	}
+}
+
+type parseUint64Test struct {
+	in  string
+	out uint64
+	err error
+}
+
+var parseUint64Tests = []parseUint64Test{
+	{"", 0, ErrSyntax},
+	{"0", 0, nil},
+	{"1", 1, nil},
+	{"12345", 12345, nil},
+	{"012345", 12345, nil},
+	{"18446744073709551616", 1<<64 - 1, ErrRange},
+	{"-1", 0, ErrSyntax},
+}
+
+type parseUint64BaseTest struct {
+	in   string
+	base int
+	out  uint64
+	err  error
+}
+
+var parseUint64BaseTests = []parseUint64BaseTest{
+	{"", 0, 0, ErrSyntax},
+	{"0", 0, 0, nil},
+	{"1", 0, 1, nil},
+	{"-1", 0, 0, ErrSyntax},
+	{"12345", 0, 12345, nil},
+	{"012345", 0, 012345, nil},
+	{"18446744073709551616", 0, 1<<64 - 1, ErrRange},
+	{"0b", 0, 0, ErrSyntax},
+	{"101", 2, 5, nil},
+	{"101_", 2, 0, ErrSyntax},
+}
+
+type parseInt64Test struct {
+	in  string
+	out int64
+	err error
+}
+
+var parseInt64Tests = []parseInt64Test{
+	{"", 0, ErrSyntax},
+	{"0", 0, nil},
+	{"1", 1, nil},
+	{"-1", -1, nil},
+	{"12345", 12345, nil},
+	{"9223372036854775808", 1<<63 - 1, ErrRange},
+	{"123%45", 0, ErrSyntax},
+}
+
+type parseInt64BaseTest struct {
+	in   string
+	base int
+	out  int64
+	err  error
+}
+
+var parseInt64BaseTests = []parseInt64BaseTest{
+	{"", 0, 0, ErrSyntax},
+	{"0", 0, 0, nil},
+	{"1", 0, 1, nil},
+	{"-1", 0, -1, nil},
+	{"12345", 0, 12345, nil},
+	{"12345", 9, 8303, nil},
+	{"012345", 0, 012345, nil},
+	{"9223372036854775808", 10, 1<<63 - 1, ErrRange},
+	{"0b", 0, 0, ErrSyntax},
+	{"101", 2, 5, nil},
+	{"101_", 2, 0, ErrSyntax},
+}
+
+type parseUint32Test struct {
+	in  string
+	out uint32
+	err error
+}
+
+var parseUint32Tests = []parseUint32Test{
+	{"", 0, ErrSyntax},
+	{"0", 0, nil},
+	{"1", 1, nil},
+	{"12345", 12345, nil},
+	{"12345x", 0, ErrSyntax},
+	{"987654321", 987654321, nil},
+	{"4294967296", 1<<32 - 1, ErrRange},
+	{"1_2_3_4_5", 0, ErrSyntax}, // base=10 so no underscores allowed
+	{"12345_", 0, ErrSyntax},
+}
+
+type parseInt32Test struct {
+	in  string
+	out int32
+	err error
+}
+
+var parseInt32Tests = []parseInt32Test{
+	{"", 0, ErrSyntax},
+	{"0", 0, nil},
+	{"-0", 0, nil},
+	{"1", 1, nil},
+	{"-1", -1, nil},
+	{"12345", 12345, nil},
+	{"-12345", -12345, nil},
+	{"2147483648", 1<<31 - 1, ErrRange},
+	{"12345_", 0, ErrSyntax},
+}
+
+type numErrorTest struct {
+	num, want string
+}
+
+var numErrorTests = []numErrorTest{
+	{"0", `strconv.ParseFloat: parsing "0": failed`},
+	{"`", "strconv.ParseFloat: parsing \"`\": failed"},
+	{"1\x00.2", `strconv.ParseFloat: parsing "1\x00.2": failed`},
+}
+
+func init() {
+	// The parse routines return NumErrors wrapping
+	// the error and the string. Convert the tables above.
+	for i := range parseUint64Tests {
+		test := &parseUint64Tests[i]
+		if test.err != nil {
+			test.err = &NumError{"ParseUint", test.in, test.err}
+		}
+	}
+	for i := range parseUint64BaseTests {
+		test := &parseUint64BaseTests[i]
+		if test.err != nil {
+			test.err = &NumError{"ParseUint", test.in, test.err}
+		}
+	}
+	for i := range parseInt64Tests {
+		test := &parseInt64Tests[i]
+		if test.err != nil {
+			test.err = &NumError{"ParseInt", test.in, test.err}
+		}
+	}
+	for i := range parseInt64BaseTests {
+		test := &parseInt64BaseTests[i]
+		if test.err != nil {
+			test.err = &NumError{"ParseInt", test.in, test.err}
+		}
+	}
+	for i := range parseUint32Tests {
+		test := &parseUint32Tests[i]
+		if test.err != nil {
+			test.err = &NumError{"ParseUint", test.in, test.err}
+		}
+	}
+	for i := range parseInt32Tests {
+		test := &parseInt32Tests[i]
+		if test.err != nil {
+			test.err = &NumError{"ParseInt", test.in, test.err}
+		}
+	}
+}
+
+func TestParseUint32(t *testing.T) {
+	for i := range parseUint32Tests {
+		test := &parseUint32Tests[i]
+		out, err := ParseUint(test.in, 10, 32)
+		if uint64(test.out) != out || !reflect.DeepEqual(test.err, err) {
+			t.Errorf("ParseUint(%q, 10, 32) = %v, %v want %v, %v",
+				test.in, out, err, test.out, test.err)
+		}
+	}
+}
+
+func TestParseUint64(t *testing.T) {
+	for i := range parseUint64Tests {
+		test := &parseUint64Tests[i]
+		out, err := ParseUint(test.in, 10, 64)
+		if test.out != out || !reflect.DeepEqual(test.err, err) {
+			t.Errorf("ParseUint(%q, 10, 64) = %v, %v want %v, %v",
+				test.in, out, err, test.out, test.err)
+		}
+	}
+}
+
+func TestParseUint64Base(t *testing.T) {
+	for i := range parseUint64BaseTests {
+		test := &parseUint64BaseTests[i]
+		out, err := ParseUint(test.in, test.base, 64)
+		if test.out != out || !reflect.DeepEqual(test.err, err) {
+			t.Errorf("ParseUint(%q, %v, 64) = %v, %v want %v, %v",
+				test.in, test.base, out, err, test.out, test.err)
+		}
+	}
+}
+
+func TestParseInt32(t *testing.T) {
+	for i := range parseInt32Tests {
+		test := &parseInt32Tests[i]
+		out, err := ParseInt(test.in, 10, 32)
+		if int64(test.out) != out || !reflect.DeepEqual(test.err, err) {
+			t.Errorf("ParseInt(%q, 10 ,32) = %v, %v want %v, %v",
+				test.in, out, err, test.out, test.err)
+		}
+	}
+}
+
+func TestParseInt64(t *testing.T) {
+	for i := range parseInt64Tests {
+		test := &parseInt64Tests[i]
+		out, err := ParseInt(test.in, 10, 64)
+		if test.out != out || !reflect.DeepEqual(test.err, err) {
+			t.Errorf("ParseInt(%q, 10, 64) = %v, %v want %v, %v",
+				test.in, out, err, test.out, test.err)
+		}
+	}
+}
+
+func TestParseInt64Base(t *testing.T) {
+	for i := range parseInt64BaseTests {
+		test := &parseInt64BaseTests[i]
+		out, err := ParseInt(test.in, test.base, 64)
+		if test.out != out || !reflect.DeepEqual(test.err, err) {
+			t.Errorf("ParseInt(%q, %v, 64) = %v, %v want %v, %v",
+				test.in, test.base, out, err, test.out, test.err)
+		}
+	}
+}
+
+func TestParseUint(t *testing.T) {
+	switch IntSize {
+	case 32:
+		for i := range parseUint32Tests {
+			test := &parseUint32Tests[i]
+			out, err := ParseUint(test.in, 10, 0)
+			if uint64(test.out) != out || !reflect.DeepEqual(test.err, err) {
+				t.Errorf("ParseUint(%q, 10, 0) = %v, %v want %v, %v",
+					test.in, out, err, test.out, test.err)
+			}
+		}
+	case 64:
+		for i := range parseUint64Tests {
+			test := &parseUint64Tests[i]
+			out, err := ParseUint(test.in, 10, 0)
+			if test.out != out || !reflect.DeepEqual(test.err, err) {
+				t.Errorf("ParseUint(%q, 10, 0) = %v, %v want %v, %v",
+					test.in, out, err, test.out, test.err)
+			}
+		}
+	}
+}
+
+func TestParseInt(t *testing.T) {
+	switch IntSize {
+	case 32:
+		for i := range parseInt32Tests {
+			test := &parseInt32Tests[i]
+			out, err := ParseInt(test.in, 10, 0)
+			if int64(test.out) != out || !reflect.DeepEqual(test.err, err) {
+				t.Errorf("ParseInt(%q, 10, 0) = %v, %v want %v, %v",
+					test.in, out, err, test.out, test.err)
+			}
+		}
+	case 64:
+		for i := range parseInt64Tests {
+			test := &parseInt64Tests[i]
+			out, err := ParseInt(test.in, 10, 0)
+			if test.out != out || !reflect.DeepEqual(test.err, err) {
+				t.Errorf("ParseInt(%q, 10, 0) = %v, %v want %v, %v",
+					test.in, out, err, test.out, test.err)
+			}
+		}
+	}
+}
+
+func TestAtoi(t *testing.T) {
+	switch IntSize {
+	case 32:
+		for i := range parseInt32Tests {
+			test := &parseInt32Tests[i]
+			out, err := Atoi(test.in)
+			var testErr error
+			if test.err != nil {
+				testErr = &NumError{"Atoi", test.in, test.err.(*NumError).Err}
+			}
+			if int(test.out) != out || !reflect.DeepEqual(testErr, err) {
+				t.Errorf("Atoi(%q) = %v, %v want %v, %v",
+					test.in, out, err, test.out, testErr)
+			}
+		}
+	case 64:
+		for i := range parseInt64Tests {
+			test := &parseInt64Tests[i]
+			out, err := Atoi(test.in)
+			var testErr error
+			if test.err != nil {
+				testErr = &NumError{"Atoi", test.in, test.err.(*NumError).Err}
+			}
+			if test.out != int64(out) || !reflect.DeepEqual(testErr, err) {
+				t.Errorf("Atoi(%q) = %v, %v want %v, %v",
+					test.in, out, err, test.out, testErr)
+			}
+		}
+	}
+}
+
+func bitSizeErrStub(name string, bitSize int) error {
+	return bitSizeError(name, "0", bitSize)
+}
+
+func baseErrStub(name string, base int) error {
+	return baseError(name, "0", base)
+}
+
+func noErrStub(name string, arg int) error {
+	return nil
+}
+
+type parseErrorTest struct {
+	arg     int
+	errStub func(name string, arg int) error
+}
+
+var parseBitSizeTests = []parseErrorTest{
+	{-1, bitSizeErrStub},
+	{0, noErrStub},
+	{64, noErrStub},
+	{65, bitSizeErrStub},
+}
+
+var parseBaseTests = []parseErrorTest{
+	{-1, baseErrStub},
+	{0, noErrStub},
+	{1, baseErrStub},
+	{2, noErrStub},
+	{36, noErrStub},
+	{37, baseErrStub},
+}
+
+func equalError(a, b error) bool {
+	if a == nil {
+		return b == nil
+	}
+	if b == nil {
+		return a == nil
+	}
+	return a.Error() == b.Error()
+}
+
+func TestParseIntBitSize(t *testing.T) {
+	for i := range parseBitSizeTests {
+		test := &parseBitSizeTests[i]
+		testErr := test.errStub("ParseInt", test.arg)
+		_, err := ParseInt("0", 0, test.arg)
+		if !equalError(testErr, err) {
+			t.Errorf("ParseInt(\"0\", 0, %v) = 0, %v want 0, %v",
+				test.arg, err, testErr)
+		}
+	}
+}
+
+func TestParseUintBitSize(t *testing.T) {
+	for i := range parseBitSizeTests {
+		test := &parseBitSizeTests[i]
+		testErr := test.errStub("ParseUint", test.arg)
+		_, err := ParseUint("0", 0, test.arg)
+		if !equalError(testErr, err) {
+			t.Errorf("ParseUint(\"0\", 0, %v) = 0, %v want 0, %v",
+				test.arg, err, testErr)
+		}
+	}
+}
+
+func TestParseIntBase(t *testing.T) {
+	for i := range parseBaseTests {
+		test := &parseBaseTests[i]
+		testErr := test.errStub("ParseInt", test.arg)
+		_, err := ParseInt("0", test.arg, 0)
+		if !equalError(testErr, err) {
+			t.Errorf("ParseInt(\"0\", %v, 0) = 0, %v want 0, %v",
+				test.arg, err, testErr)
+		}
+	}
+}
+
+func TestParseUintBase(t *testing.T) {
+	for i := range parseBaseTests {
+		test := &parseBaseTests[i]
+		testErr := test.errStub("ParseUint", test.arg)
+		_, err := ParseUint("0", test.arg, 0)
+		if !equalError(testErr, err) {
+			t.Errorf("ParseUint(\"0\", %v, 0) = 0, %v want 0, %v",
+				test.arg, err, testErr)
+		}
+	}
+}
+
+func TestNumError(t *testing.T) {
+	for _, test := range numErrorTests {
+		err := &NumError{
+			Func: "ParseFloat",
+			Num:  test.num,
+			Err:  errors.New("failed"),
+		}
+		if got := err.Error(); got != test.want {
+			t.Errorf(`(&NumError{"ParseFloat", %q, "failed"}).Error() = %v, want %v`, test.num, got, test.want)
+		}
+	}
+}
+
+func TestNumErrorUnwrap(t *testing.T) {
+	err := &NumError{Err: ErrSyntax}
+	if !errors.Is(err, ErrSyntax) {
+		t.Error("errors.Is failed, wanted success")
+	}
+}
+
+func TestFormatComplex(t *testing.T) {
+	tests := []struct {
+		c       complex128
+		fmt     byte
+		prec    int
+		bitSize int
+		out     string
+	}{
+		// a variety of signs
+		{1 + 2i, 'g', -1, 128, "(1+2i)"},
+		{3 - 4i, 'g', -1, 128, "(3-4i)"},
+		{-5 + 6i, 'g', -1, 128, "(-5+6i)"},
+		{-7 - 8i, 'g', -1, 128, "(-7-8i)"},
+
+		// test that fmt and prec are working
+		{3.14159 + 0.00123i, 'e', 3, 128, "(3.142e+00+1.230e-03i)"},
+		{3.14159 + 0.00123i, 'f', 3, 128, "(3.142+0.001i)"},
+		{3.14159 + 0.00123i, 'g', 3, 128, "(3.14+0.00123i)"},
+
+		// ensure bitSize rounding is working
+		{1.2345678901234567 + 9.876543210987654i, 'f', -1, 128, "(1.2345678901234567+9.876543210987654i)"},
+		{1.2345678901234567 + 9.876543210987654i, 'f', -1, 64, "(1.2345679+9.876543i)"},
+
+		// other cases are handled by FormatFloat tests
+	}
+	for _, test := range tests {
+		out := FormatComplex(test.c, test.fmt, test.prec, test.bitSize)
+		if out != test.out {
+			t.Fatalf("FormatComplex(%v, %q, %d, %d) = %q; want %q",
+				test.c, test.fmt, test.prec, test.bitSize, out, test.out)
+		}
+	}
+}
+
+func TestFormatComplexInvalidBitSize(t *testing.T) {
+	defer func() {
+		if r := recover(); r == nil {
+			t.Fatalf("expected panic due to invalid bitSize")
+		}
+	}()
+	_ = FormatComplex(1+2i, 'g', -1, 100)
+}
+
+type itob64Test struct {
+	in   int64
+	base int
+	out  string
+}
+
+var itob64tests = []itob64Test{
+	{0, 10, "0"},
+	{1, 10, "1"},
+	{-1, 10, "-1"},
+	{12345678, 10, "12345678"},
+	{-1 << 63, 10, "-9223372036854775808"},
+	{16, 17, "g"},
+	{25, 25, "10"},
+	{(((((17*36+24)*36+21)*36+34)*36+12)*36+24)*36 + 32, 36, "holycow"},
+}
+
+func TestItoa(t *testing.T) {
+	for _, test := range itob64tests {
+		s := FormatInt(test.in, test.base)
+		if s != test.out {
+			t.Errorf("FormatInt(%v, %v) = %v want %v",
+				test.in, test.base, s, test.out)
+		}
+		x := AppendInt([]byte("abc"), test.in, test.base)
+		if string(x) != "abc"+test.out {
+			t.Errorf("AppendInt(%q, %v, %v) = %q want %v",
+				"abc", test.in, test.base, x, test.out)
+		}
+
+		if test.in >= 0 {
+			s := FormatUint(uint64(test.in), test.base)
+			if s != test.out {
+				t.Errorf("FormatUint(%v, %v) = %v want %v",
+					test.in, test.base, s, test.out)
+			}
+			x := AppendUint(nil, uint64(test.in), test.base)
+			if string(x) != test.out {
+				t.Errorf("AppendUint(%q, %v, %v) = %q want %v",
+					"abc", uint64(test.in), test.base, x, test.out)
+			}
+		}
+
+		if test.base == 10 && int64(int(test.in)) == test.in {
+			s := Itoa(int(test.in))
+			if s != test.out {
+				t.Errorf("Itoa(%v) = %v want %v",
+					test.in, s, test.out)
+			}
+		}
+	}
+
+	// Override when base is illegal
+	defer func() {
+		if r := recover(); r == nil {
+			t.Fatalf("expected panic due to illegal base")
+		}
+	}()
+	FormatUint(12345678, 1)
+}
+
+type uitob64Test struct {
+	in   uint64
+	base int
+	out  string
+}
+
+var uitob64tests = []uitob64Test{
+	{1<<63 - 1, 10, "9223372036854775807"},
+	{1 << 63, 10, "9223372036854775808"},
+	{1<<63 + 1, 10, "9223372036854775809"},
+	{1<<64 - 2, 10, "18446744073709551614"},
+	{1<<64 - 1, 10, "18446744073709551615"},
+	{1<<64 - 1, 2, "1111111111111111111111111111111111111111111111111111111111111111"},
+}
+
+func TestUitoa(t *testing.T) {
+	for _, test := range uitob64tests {
+		s := FormatUint(test.in, test.base)
+		if s != test.out {
+			t.Errorf("FormatUint(%v, %v) = %v want %v",
+				test.in, test.base, s, test.out)
+		}
+		x := AppendUint([]byte("abc"), test.in, test.base)
+		if string(x) != "abc"+test.out {
+			t.Errorf("AppendUint(%q, %v, %v) = %q want %v",
+				"abc", test.in, test.base, x, test.out)
+		}
+
+	}
+}
+
+var varlenUints = []struct {
+	in  uint64
+	out string
+}{
+	{1, "1"},
+	{12, "12"},
+	{123, "123"},
+	{1234, "1234"},
+	{12345, "12345"},
+	{123456, "123456"},
+	{1234567, "1234567"},
+	{12345678, "12345678"},
+	{123456789, "123456789"},
+	{1234567890, "1234567890"},
+	{12345678901, "12345678901"},
+	{123456789012, "123456789012"},
+	{1234567890123, "1234567890123"},
+	{12345678901234, "12345678901234"},
+	{123456789012345, "123456789012345"},
+	{1234567890123456, "1234567890123456"},
+	{12345678901234567, "12345678901234567"},
+	{123456789012345678, "123456789012345678"},
+	{1234567890123456789, "1234567890123456789"},
+	{12345678901234567890, "12345678901234567890"},
+}
+
+func TestFormatUintVarlen(t *testing.T) {
+	for _, test := range varlenUints {
+		s := FormatUint(test.in, 10)
+		if s != test.out {
+			t.Errorf("FormatUint(%v, 10) = %v want %v", test.in, s, test.out)
+		}
+	}
+}