1 files changed, 79 insertions, 0 deletions
diff --git a/src/runtime/float.go b/src/runtime/float.go
index 9f281c4045..d8573c103b 100644
--- a/src/runtime/float.go
+++ b/src/runtime/float.go
@@ -6,6 +6,12 @@ package runtime
 
 import "unsafe"
 
+const (
+	float64Mask  = 0x7FF
+	float64Shift = 64 - 11 - 1
+	float64Bias  = 1023
+)
+
 var inf = float64frombits(0x7FF0000000000000)
 
 // isNaN reports whether f is an IEEE 754 “not-a-number” value.
@@ -52,3 +58,76 @@ func float64bits(f float64) uint64 {
 func float64frombits(b uint64) float64 {
 	return *(*float64)(unsafe.Pointer(&b))
 }
+
+// floor returns the greatest integer value less than or equal to x.
+//
+// Special cases are:
+//
+//	floor(±0) = ±0
+//	floor(±Inf) = ±Inf
+//	floor(NaN) = NaN
+//
+// N.B. Portable floor copied from math. math also has optimized arch-specific
+// implementations.
+func floor(x float64) float64 {
+	if x == 0 || isNaN(x) || isInf(x) {
+		return x
+	}
+	if x < 0 {
+		d, fract := modf(-x)
+		if fract != 0.0 {
+			d = d + 1
+		}
+		return -d
+	}
+	d, _ := modf(x)
+	return d
+}
+
+// ceil returns the least integer value greater than or equal to x.
+//
+// Special cases are:
+//
+//	Ceil(±0) = ±0
+//	Ceil(±Inf) = ±Inf
+//	Ceil(NaN) = NaN
+//
+// N.B. Portable ceil copied from math. math also has optimized arch-specific
+// implementations.
+func ceil(x float64) float64 {
+	return -floor(-x)
+}
+
+// modf returns integer and fractional floating-point numbers
+// that sum to f. Both values have the same sign as f.
+//
+// Special cases are:
+//
+//	Modf(±Inf) = ±Inf, NaN
+//	Modf(NaN) = NaN, NaN
+//
+// N.B. Portable modf copied from math. math also has optimized arch-specific
+// implementations.
+func modf(f float64) (int float64, frac float64) {
+	if f < 1 {
+		switch {
+		case f < 0:
+			int, frac = modf(-f)
+			return -int, -frac
+		case f == 0:
+			return f, f // Return -0, -0 when f == -0
+		}
+		return 0, f
+	}
+
+	x := float64bits(f)
+	e := uint(x>>float64Shift)&float64Mask - float64Bias
+
+	// Keep the top 12+e bits, the integer part; clear the rest.
+	if e < 64-12 {
+		x &^= 1<<(64-12-e) - 1
+	}
+	int = float64frombits(x)
+	frac = f - int
+	return
+}