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// 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<<shift - 1
for u >= 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
}
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