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 } 93
