// Copyright 2017 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build ignore
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// This program generates bits_tables.go.
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package main
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import (
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"bytes"
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"fmt"
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"go/format"
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"io"
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"io/ioutil"
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"log"
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)
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var header = []byte(`// Copyright 2017 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Code generated by go run make_tables.go. DO NOT EDIT.
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package bits
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`)
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func main() {
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buf := bytes.NewBuffer(header)
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gen(buf, "ntz8tab", ntz8)
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gen(buf, "pop8tab", pop8)
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gen(buf, "rev8tab", rev8)
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gen(buf, "len8tab", len8)
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out, err := format.Source(buf.Bytes())
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if err != nil {
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log.Fatal(err)
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}
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err = ioutil.WriteFile("bits_tables.go", out, 0666)
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if err != nil {
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log.Fatal(err)
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}
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}
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func gen(w io.Writer, name string, f func(uint8) uint8) {
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fmt.Fprintf(w, "var %s = [256]uint8{", name)
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for i := 0; i < 256; i++ {
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if i%16 == 0 {
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fmt.Fprint(w, "\n\t")
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} else {
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fmt.Fprint(w, " ")
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}
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fmt.Fprintf(w, "%#02x,", f(uint8(i)))
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}
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fmt.Fprint(w, "\n}\n\n")
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}
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func ntz8(x uint8) (n uint8) {
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for x&1 == 0 && n < 8 {
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x >>= 1
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n++
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}
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return
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}
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func pop8(x uint8) (n uint8) {
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for x != 0 {
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x &= x - 1
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n++
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}
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return
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}
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func rev8(x uint8) (r uint8) {
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for i := 8; i > 0; i-- {
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r = r<<1 | x&1
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x >>= 1
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}
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return
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}
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func len8(x uint8) (n uint8) {
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for x != 0 {
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x >>= 1
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n++
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}
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return
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}
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