math/bits: examples generator

Change-Id: Icdd0566d3b7dbc034256e16f8a6b6f1af07069b3
Reviewed-on: https://go-review.googlesource.com/54350
Reviewed-by: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 174 insertions, 0 deletions

diff --git a/src/math/bits/make_examples.go b/src/math/bits/make_examples.go
new file mode 100644
index 0000000000..caef0b1b69
--- /dev/null
+++ b/src/math/bits/make_examples.go
@@ -0,0 +1,174 @@
+// 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.
+
+// +build ignore
+
+// This program generates example_test.go.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"go/format"
+	"io"
+	"io/ioutil"
+	"log"
+	"math/bits"
+	"sort"
+)
+
+var (
+	header = []byte(`// 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.
+
+// Code generated by go run make_examples.go. DO NOT EDIT.
+
+package bits_test
+
+import (
+	"fmt"
+	"math/bits"
+)
+
+`)
+
+	exampleRegF = `
+func Example%s() {
+	fmt.Printf("%s\n", %d, bits.%s(%d))
+	// Output:
+	// %s
+}
+`
+	exampleRevF = `
+func Example%s() {
+	fmt.Printf("%s\n", %d)
+	fmt.Printf("%s\n", bits.%s(%d))
+	// Output:
+	// %s
+	// %s
+}
+`
+)
+
+func main() {
+	buf := bytes.NewBuffer(header)
+
+	genReg(buf)
+	genRev(buf)
+
+	out, err := format.Source(buf.Bytes())
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	err = ioutil.WriteFile("example_test.go", out, 0666)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func genReg(w io.Writer) {
+	examples := []struct {
+		name string
+		in   int
+		out  map[uint]interface{}
+	}{
+		{
+			name: "LeadingZeros",
+			in:   1,
+			out: map[uint]interface{}{
+				8:  bits.LeadingZeros8(1),
+				16: bits.LeadingZeros16(1),
+				32: bits.LeadingZeros32(1),
+				64: bits.LeadingZeros64(1),
+			},
+		}, {
+			name: "TrailingZeros",
+			in:   14,
+			out: map[uint]interface{}{
+				8:  bits.TrailingZeros8(14),
+				16: bits.TrailingZeros16(14),
+				32: bits.TrailingZeros32(14),
+				64: bits.TrailingZeros64(14),
+			},
+		}, {
+			name: "OnesCount",
+			in:   14,
+			out: map[uint]interface{}{
+				8:  bits.OnesCount8(14),
+				16: bits.OnesCount16(14),
+				32: bits.OnesCount32(14),
+				64: bits.OnesCount64(14),
+			},
+		}, {
+			name: "Len",
+			in:   8,
+			out: map[uint]interface{}{
+				8:  bits.Len8(8),
+				16: bits.Len16(8),
+				32: bits.Len32(8),
+				64: bits.Len64(8),
+			},
+		},
+	}
+
+	for _, e := range examples {
+		sizes := sortedSizes(e.out)
+
+		for _, size := range sizes {
+			fnName := fmt.Sprintf("%s%d", e.name, size)
+			outF := fmt.Sprintf("%s(%%0%db) = %%d", fnName, size)
+			out := fmt.Sprintf(outF, e.in, e.out[size])
+
+			fmt.Fprintf(w, exampleRegF, fnName, outF, e.in, fnName, e.in, out)
+		}
+	}
+}
+
+func genRev(w io.Writer) {
+	examples := []struct {
+		name string
+		in   int
+		out  map[uint]interface{}
+	}{
+		{
+			name: "Reverse",
+			in:   19,
+			out: map[uint]interface{}{
+				8:  bits.Reverse8(19),
+				16: bits.Reverse16(19),
+				32: bits.Reverse32(19),
+				64: bits.Reverse64(19),
+			},
+		},
+	}
+
+	for _, e := range examples {
+		sizes := sortedSizes(e.out)
+
+		for _, size := range sizes {
+			fnName := fmt.Sprintf("%s%d", e.name, size)
+			outF := fmt.Sprintf("%%0%db", size)
+			out := fmt.Sprintf(outF, e.in)
+			secOut := fmt.Sprintf(outF, e.out[size])
+
+			fmt.Fprintf(w, exampleRevF, fnName, outF, e.in, outF, fnName, e.in, out, secOut)
+		}
+	}
+}
+
+func sortedSizes(out map[uint]interface{}) []uint {
+	sizes := make([]uint, 0, len(out))
+	for size := range out {
+		sizes = append(sizes, size)
+	}
+
+	sort.Slice(sizes, func(i, j int) bool {
+		return sizes[i] < sizes[j]
+	})
+
+	return sizes
+}