// Copyright 2009 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. package strconv import "math/bits" const fastSmalls = true // enable fast path for small integers // FormatUint returns the string representation of i in the given base, // for 2 <= base <= 36. The result uses the lower-case letters 'a' to 'z' // for digit values >= 10. func FormatUint(i uint64, base int) string { if fastSmalls && i < nSmalls && base == 10 { return small(int(i)) } _, s := formatBits(nil, i, base, false, false) return s } // FormatInt returns the string representation of i in the given base, // for 2 <= base <= 36. The result uses the lower-case letters 'a' to 'z' // for digit values >= 10. func FormatInt(i int64, base int) string { if fastSmalls && 0 <= i && i < nSmalls && base == 10 { return small(int(i)) } _, s := formatBits(nil, uint64(i), base, i < 0, false) return s } // Itoa is equivalent to FormatInt(int64(i), 10). func Itoa(i int) string { return FormatInt(int64(i), 10) } // AppendInt appends the string form of the integer i, // as generated by FormatInt, to dst and returns the extended buffer. func AppendInt(dst []byte, i int64, base int) []byte { if fastSmalls && 0 <= i && i < nSmalls && base == 10 { return append(dst, small(int(i))...) } dst, _ = formatBits(dst, uint64(i), base, i < 0, true) return dst } // AppendUint appends the string form of the unsigned integer i, // as generated by FormatUint, to dst and returns the extended buffer. func AppendUint(dst []byte, i uint64, base int) []byte { if fastSmalls && i < nSmalls && base == 10 { return append(dst, small(int(i))...) } dst, _ = formatBits(dst, i, base, false, true) return dst } // small returns the string for an i with 0 <= i < nSmalls. func small(i int) string { if i < 10 { return digits[i : i+1] } return smallsString[i*2 : i*2+2] } const nSmalls = 100 const smallsString = "00010203040506070809" + "10111213141516171819" + "20212223242526272829" + "30313233343536373839" + "40414243444546474849" + "50515253545556575859" + "60616263646566676869" + "70717273747576777879" + "80818283848586878889" + "90919293949596979899" const host32bit = ^uint(0)>>32 == 0 const digits = "0123456789abcdefghijklmnopqrstuvwxyz" // formatBits computes the string representation of u in the given base. // If neg is set, u is treated as negative int64 value. If append_ is // set, the string is appended to dst and the resulting byte slice is // returned as the first result value; otherwise the string is returned // as the second result value. func formatBits(dst []byte, u uint64, base int, neg, append_ bool) (d []byte, s string) { if base < 2 || base > len(digits) { panic("strconv: illegal AppendInt/FormatInt base") } // 2 <= base && base <= len(digits) var a [64 + 1]byte // +1 for sign of 64bit value in base 2 i := len(a) if neg { u = -u } // convert bits // We use uint values where we can because those will // fit into a single register even on a 32bit machine. if base == 10 { // common case: use constants for / because // the compiler can optimize it into a multiply+shift if host32bit { // convert the lower digits using 32bit operations for u >= 1e9 { // Avoid using r = a%b in addition to q = a/b // since 64bit division and modulo operations // are calculated by runtime functions on 32bit machines. q := u / 1e9 us := uint(u - q*1e9) // u % 1e9 fits into a uint for j := 4; j > 0; j-- { is := us % 100 * 2 us /= 100 i -= 2 a[i+1] = smallsString[is+1] a[i+0] = smallsString[is+0] } // us < 10, since it contains the last digit // from the initial 9-digit us. i-- a[i] = smallsString[us*2+1] u = q } // u < 1e9 } // u guaranteed to fit into a uint us := uint(u) for us >= 100 { is := us % 100 * 2 us /= 100 i -= 2 a[i+1] = smallsString[is+1] a[i+0] = smallsString[is+0] } // us < 100 is := us * 2 i-- a[i] = smallsString[is+1] if us >= 10 { i-- a[i] = smallsString[is] } } else if isPowerOfTwo(base) { // Use shifts and masks instead of / and %. // Base is a power of 2 and 2 <= base <= len(digits) where len(digits) is 36. // The largest power of 2 below or equal to 36 is 32, which is 1 << 5; // i.e., the largest possible shift count is 5. By &-ind that value with // the constant 7 we tell the compiler that the shift count is always // less than 8 which is smaller than any register width. This allows // the compiler to generate better code for the shift operation. shift := uint(bits.TrailingZeros(uint(base))) & 7 b := uint64(base) m := uint(base) - 1 // == 1<= b { i-- a[i] = digits[uint(u)&m] u >>= shift } // u < base i-- a[i] = digits[uint(u)] } else { // general case b := uint64(base) for u >= b { i-- // Avoid using r = a%b in addition to q = a/b // since 64bit division and modulo operations // are calculated by runtime functions on 32bit machines. q := u / b a[i] = digits[uint(u-q*b)] u = q } // u < base i-- a[i] = digits[uint(u)] } // add sign, if any if neg { i-- a[i] = '-' } if append_ { d = append(dst, a[i:]...) return } s = string(a[i:]) return } func isPowerOfTwo(x int) bool { return x&(x-1) == 0 }