libgo/go/strconv/itoa.go

   1 // Copyright 2009 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 package strconv
   6
   7 // FormatUint returns the string representation of i in the given base,
   8 // for 2 <= base <= 36. The result uses the lower-case letters 'a' to 'z'
   9 // for digit values >= 10.
  10 func FormatUint(i uint64, base int) string {
  11         _, s := formatBits(nil, i, base, false, false)
  12         return s
  13 }
  14
  15 // FormatInt returns the string representation of i in the given base,
  16 // for 2 <= base <= 36. The result uses the lower-case letters 'a' to 'z'
  17 // for digit values >= 10.
  18 func FormatInt(i int64, base int) string {
  19         _, s := formatBits(nil, uint64(i), base, i < 0, false)
  20         return s
  21 }
  22
  23 // Itoa is shorthand for FormatInt(i, 10).
  24 func Itoa(i int) string {
  25         return FormatInt(int64(i), 10)
  26 }
  27
  28 // AppendInt appends the string form of the integer i,
  29 // as generated by FormatInt, to dst and returns the extended buffer.
  30 func AppendInt(dst []byte, i int64, base int) []byte {
  31         dst, _ = formatBits(dst, uint64(i), base, i < 0, true)
  32         return dst
  33 }
  34
  35 // AppendUint appends the string form of the unsigned integer i,
  36 // as generated by FormatUint, to dst and returns the extended buffer.
  37 func AppendUint(dst []byte, i uint64, base int) []byte {
  38         dst, _ = formatBits(dst, i, base, false, true)
  39         return dst
  40 }
  41
  42 const (
  43         digits   = "0123456789abcdefghijklmnopqrstuvwxyz"
  44         digits01 = "0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789"
  45         digits10 = "0000000000111111111122222222223333333333444444444455555555556666666666777777777788888888889999999999"
  46 )
  47
  48 var shifts = [len(digits) + 1]uint{
  49         1 << 1: 1,
  50         1 << 2: 2,
  51         1 << 3: 3,
  52         1 << 4: 4,
  53         1 << 5: 5,
  54 }
  55
  56 // formatBits computes the string representation of u in the given base.
  57 // If neg is set, u is treated as negative int64 value. If append_ is
  58 // set, the string is appended to dst and the resulting byte slice is
  59 // returned as the first result value; otherwise the string is returned
  60 // as the second result value.
  61 //
  62 func formatBits(dst []byte, u uint64, base int, neg, append_ bool) (d []byte, s string) {
  63         if base < 2 || base > len(digits) {
  64                 panic("strconv: illegal AppendInt/FormatInt base")
  65         }
  66         // 2 <= base && base <= len(digits)
  67
  68         var a [64 + 1]byte // +1 for sign of 64bit value in base 2
  69         i := len(a)
  70
  71         if neg {
  72                 u = -u
  73         }
  74
  75         // convert bits
  76         if base == 10 {
  77                 // common case: use constants for / and % because
  78                 // the compiler can optimize it into a multiply+shift,
  79                 // and unroll loop
  80                 for u >= 100 {
  81                         i -= 2
  82                         q := u / 100
  83                         j := uintptr(u - q*100)
  84                         a[i+1] = digits01[j]
  85                         a[i+0] = digits10[j]
  86                         u = q
  87                 }
  88                 if u >= 10 {
  89                         i--
  90                         q := u / 10
  91                         a[i] = digits[uintptr(u-q*10)]
  92                         u = q
  93                 }
  94
  95         } else if s := shifts[base]; s > 0 {
  96                 // base is power of 2: use shifts and masks instead of / and %
  97                 b := uint64(base)
  98                 m := uintptr(b) - 1 // == 1<<s - 1
  99                 for u >= b {
 100                         i--
 101                         a[i] = digits[uintptr(u)&m]
 102                         u >>= s
 103                 }
 104
 105         } else {
 106                 // general case
 107                 b := uint64(base)
 108                 for u >= b {
 109                         i--
 110                         a[i] = digits[uintptr(u%b)]
 111                         u /= b
 112                 }
 113         }
 114
 115         // u < base
 116         i--
 117         a[i] = digits[uintptr(u)]
 118
 119         // add sign, if any
 120         if neg {
 121                 i--
 122                 a[i] = '-'
 123         }
 124
 125         if append_ {
 126                 d = append(dst, a[i:]...)
 127                 return
 128         }
 129         s = string(a[i:])
 130         return
 131 }