Source file src/pkg/math/bits/make_tables.go
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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 }
93
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