1 files changed, 92 insertions, 0 deletions
diff --git a/src/math/bits/make_tables.go b/src/math/bits/make_tables.go
new file mode 100644
index 0000000..867025e
--- /dev/null
+++ b/src/math/bits/make_tables.go
@@ -0,0 +1,92 @@
+// 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.
+
+//go:build ignore
+// +build ignore
+
+// This program generates bits_tables.go.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"go/format"
+	"io"
+	"log"
+	"os"
+)
+
+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_tables.go. DO NOT EDIT.
+
+package bits
+
+`)
+
+func main() {
+	buf := bytes.NewBuffer(header)
+
+	gen(buf, "ntz8tab", ntz8)
+	gen(buf, "pop8tab", pop8)
+	gen(buf, "rev8tab", rev8)
+	gen(buf, "len8tab", len8)
+
+	out, err := format.Source(buf.Bytes())
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	err = os.WriteFile("bits_tables.go", out, 0666)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func gen(w io.Writer, name string, f func(uint8) uint8) {
+	// Use a const string to allow the compiler to constant-evaluate lookups at constant index.
+	fmt.Fprintf(w, "const %s = \"\"+\n\"", name)
+	for i := 0; i < 256; i++ {
+		fmt.Fprintf(w, "\\x%02x", f(uint8(i)))
+		if i%16 == 15 && i != 255 {
+			fmt.Fprint(w, "\"+\n\"")
+		}
+	}
+	fmt.Fprint(w, "\"\n\n")
+}
+
+func ntz8(x uint8) (n uint8) {
+	for x&1 == 0 && n < 8 {
+		x >>= 1
+		n++
+	}
+	return
+}
+
+func pop8(x uint8) (n uint8) {
+	for x != 0 {
+		x &= x - 1
+		n++
+	}
+	return
+}
+
+func rev8(x uint8) (r uint8) {
+	for i := 8; i > 0; i-- {
+		r = r<<1 | x&1
+		x >>= 1
+	}
+	return
+}
+
+func len8(x uint8) (n uint8) {
+	for x != 0 {
+		x >>= 1
+		n++
+	}
+	return
+}