libgo/go/math/bits/make_tables.go

   1 // Copyright 2017 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // +build ignore
   6
   7 // This program generates bits_tables.go.
   8
   9 package main
  10
  11 import (
  12         "bytes"
  13         "fmt"
  14         "go/format"
  15         "io"
  16         "io/ioutil"
  17         "log"
  18 )
  19
  20 var header = []byte(`// Copyright 2017 The Go Authors. All rights reserved.
  21 // Use of this source code is governed by a BSD-style
  22 // license that can be found in the LICENSE file.
  23
  24 // Code generated by go run make_tables.go. DO NOT EDIT.
  25
  26 package bits
  27
  28 `)
  29
  30 func main() {
  31         buf := bytes.NewBuffer(header)
  32
  33         gen(buf, "ntz8tab", ntz8)
  34         gen(buf, "pop8tab", pop8)
  35         gen(buf, "rev8tab", rev8)
  36         gen(buf, "len8tab", len8)
  37
  38         out, err := format.Source(buf.Bytes())
  39         if err != nil {
  40                 log.Fatal(err)
  41         }
  42
  43         err = ioutil.WriteFile("bits_tables.go", out, 0666)
  44         if err != nil {
  45                 log.Fatal(err)
  46         }
  47 }
  48
  49 func gen(w io.Writer, name string, f func(uint8) uint8) {
  50         fmt.Fprintf(w, "var %s = [256]uint8{", name)
  51         for i := 0; i < 256; i++ {
  52                 if i%16 == 0 {
  53                         fmt.Fprint(w, "\n\t")
  54                 } else {
  55                         fmt.Fprint(w, " ")
  56                 }
  57                 fmt.Fprintf(w, "%#02x,", f(uint8(i)))
  58         }
  59         fmt.Fprint(w, "\n}\n\n")
  60 }
  61
  62 func ntz8(x uint8) (n uint8) {
  63         for x&1 == 0 && n < 8 {
  64                 x >>= 1
  65                 n++
  66         }
  67         return
  68 }
  69
  70 func pop8(x uint8) (n uint8) {
  71         for x != 0 {
  72                 x &= x - 1
  73                 n++
  74         }
  75         return
  76 }
  77
  78 func rev8(x uint8) (r uint8) {
  79         for i := 8; i > 0; i-- {
  80                 r = r<<1 | x&1
  81                 x >>= 1
  82         }
  83         return
  84 }
  85
  86 func len8(x uint8) (n uint8) {
  87         for x != 0 {
  88                 x >>= 1
  89                 n++
  90         }
  91         return
  92 }