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(int64(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 ) 45 46 var shifts = [len(digits) + 1]uint{ 47 1 << 1: 1, 48 1 << 2: 2, 49 1 << 3: 3, 50 1 << 4: 4, 51 1 << 5: 5, 52 } 53 54 // formatBits computes the string representation of u in the given base. 55 // If neg is set, u is treated as negative int64 value. If append_ is 56 // set, the string is appended to dst and the resulting byte slice is 57 // returned as the first result value; otherwise the string is returned 58 // as the second result value. 59 // 60 func formatBits(dst []byte, u uint64, base int, neg, append_ bool) (d []byte, s string) { 61 if base < 2 || base > len(digits) { 62 panic("strconv: illegal AppendInt/FormatInt base") 63 } 64 // 2 <= base && base <= len(digits) 65 66 var a [64 + 1]byte // +1 for sign of 64bit value in base 2 67 i := len(a) 68 69 if neg { 70 u = -u 71 } 72 73 // convert bits 74 if base == 10 { 75 // common case: use constants for / because 76 // the compiler can optimize it into a multiply+shift 77 78 if ^uintptr(0)>>32 == 0 { 79 for u > uint64(^uintptr(0)) { 80 q := u / 1e9 81 us := uintptr(u - q*1e9) // us % 1e9 fits into a uintptr 82 for j := 9; j > 0; j-- { 83 i-- 84 qs := us / 10 85 a[i] = byte(us - qs*10 + '0') 86 us = qs 87 } 88 u = q 89 } 90 } 91 92 // u guaranteed to fit into a uintptr 93 us := uintptr(u) 94 for us >= 10 { 95 i-- 96 q := us / 10 97 a[i] = byte(us - q*10 + '0') 98 us = q 99 } 100 // u < 10 101 i-- 102 a[i] = byte(us + '0') 103 104 } else if s := shifts[base]; s > 0 { 105 // base is power of 2: use shifts and masks instead of / and % 106 b := uint64(base) 107 m := uintptr(b) - 1 // == 1<<s - 1 108 for u >= b { 109 i-- 110 a[i] = digits[uintptr(u)&m] 111 u >>= s 112 } 113 // u < base 114 i-- 115 a[i] = digits[uintptr(u)] 116 117 } else { 118 // general case 119 b := uint64(base) 120 for u >= b { 121 i-- 122 q := u / b 123 a[i] = digits[uintptr(u-q*b)] 124 u = q 125 } 126 // u < base 127 i-- 128 a[i] = digits[uintptr(u)] 129 } 130 131 // add sign, if any 132 if neg { 133 i-- 134 a[i] = '-' 135 } 136 137 if append_ { 138 d = append(dst, a[i:]...) 139 return 140 } 141 s = string(a[i:]) 142 return 143 } 144
