1 files changed, 112 insertions, 0 deletions
diff --git a/src/math/bits/make_examples.go b/src/math/bits/make_examples.go
new file mode 100644
index 0000000..1d3ad53
--- /dev/null
+++ b/src/math/bits/make_examples.go
@@ -0,0 +1,112 @@
+// 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"
+	"log"
+	"math/bits"
+	"os"
+)
+
+const header = `// 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"
+)
+`
+
+func main() {
+	w := bytes.NewBuffer([]byte(header))
+
+	for _, e := range []struct {
+		name string
+		in   int
+		out  [4]interface{}
+		out2 [4]interface{}
+	}{
+		{
+			name: "LeadingZeros",
+			in:   1,
+			out:  [4]interface{}{bits.LeadingZeros8(1), bits.LeadingZeros16(1), bits.LeadingZeros32(1), bits.LeadingZeros64(1)},
+		},
+		{
+			name: "TrailingZeros",
+			in:   14,
+			out:  [4]interface{}{bits.TrailingZeros8(14), bits.TrailingZeros16(14), bits.TrailingZeros32(14), bits.TrailingZeros64(14)},
+		},
+		{
+			name: "OnesCount",
+			in:   14,
+			out:  [4]interface{}{bits.OnesCount8(14), bits.OnesCount16(14), bits.OnesCount32(14), bits.OnesCount64(14)},
+		},
+		{
+			name: "RotateLeft",
+			in:   15,
+			out:  [4]interface{}{bits.RotateLeft8(15, 2), bits.RotateLeft16(15, 2), bits.RotateLeft32(15, 2), bits.RotateLeft64(15, 2)},
+			out2: [4]interface{}{bits.RotateLeft8(15, -2), bits.RotateLeft16(15, -2), bits.RotateLeft32(15, -2), bits.RotateLeft64(15, -2)},
+		},
+		{
+			name: "Reverse",
+			in:   19,
+			out:  [4]interface{}{bits.Reverse8(19), bits.Reverse16(19), bits.Reverse32(19), bits.Reverse64(19)},
+		},
+		{
+			name: "ReverseBytes",
+			in:   15,
+			out:  [4]interface{}{nil, bits.ReverseBytes16(15), bits.ReverseBytes32(15), bits.ReverseBytes64(15)},
+		},
+		{
+			name: "Len",
+			in:   8,
+			out:  [4]interface{}{bits.Len8(8), bits.Len16(8), bits.Len32(8), bits.Len64(8)},
+		},
+	} {
+		for i, size := range []int{8, 16, 32, 64} {
+			if e.out[i] == nil {
+				continue // function doesn't exist
+			}
+			f := fmt.Sprintf("%s%d", e.name, size)
+			fmt.Fprintf(w, "\nfunc Example%s() {\n", f)
+			switch e.name {
+			case "RotateLeft", "Reverse", "ReverseBytes":
+				fmt.Fprintf(w, "\tfmt.Printf(\"%%0%db\\n\", %d)\n", size, e.in)
+				if e.name == "RotateLeft" {
+					fmt.Fprintf(w, "\tfmt.Printf(\"%%0%db\\n\", bits.%s(%d, 2))\n", size, f, e.in)
+					fmt.Fprintf(w, "\tfmt.Printf(\"%%0%db\\n\", bits.%s(%d, -2))\n", size, f, e.in)
+				} else {
+					fmt.Fprintf(w, "\tfmt.Printf(\"%%0%db\\n\", bits.%s(%d))\n", size, f, e.in)
+				}
+				fmt.Fprintf(w, "\t// Output:\n")
+				fmt.Fprintf(w, "\t// %0*b\n", size, e.in)
+				fmt.Fprintf(w, "\t// %0*b\n", size, e.out[i])
+				if e.name == "RotateLeft" && e.out2[i] != nil {
+					fmt.Fprintf(w, "\t// %0*b\n", size, e.out2[i])
+				}
+			default:
+				fmt.Fprintf(w, "\tfmt.Printf(\"%s(%%0%db) = %%d\\n\", %d, bits.%s(%d))\n", f, size, e.in, f, e.in)
+				fmt.Fprintf(w, "\t// Output:\n")
+				fmt.Fprintf(w, "\t// %s(%0*b) = %d\n", f, size, e.in, e.out[i])
+			}
+			fmt.Fprintf(w, "}\n")
+		}
+	}
+
+	if err := os.WriteFile("example_test.go", w.Bytes(), 0666); err != nil {
+		log.Fatal(err)
+	}
+}