114 lines
2.6 KiB
Go
114 lines
2.6 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package strconv
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// FormatUint returns the string representation of i in the given base.
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func FormatUint(i uint64, base int) string {
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_, s := formatBits(nil, i, base, false, false)
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return s
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}
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// FormatInt returns the string representation of i in the given base.
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func FormatInt(i int64, base int) string {
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_, s := formatBits(nil, uint64(i), base, i < 0, false)
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return s
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}
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// Itoa is shorthand for FormatInt(i, 10).
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func Itoa(i int) string {
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return FormatInt(int64(i), 10)
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}
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// AppendInt appends the string form of the integer i,
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// as generated by FormatInt, to dst and returns the extended buffer.
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func AppendInt(dst []byte, i int64, base int) []byte {
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dst, _ = formatBits(dst, uint64(i), base, i < 0, true)
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return dst
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}
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// AppendUint appends the string form of the unsigned integer i,
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// as generated by FormatUint, to dst and returns the extended buffer.
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func AppendUint(dst []byte, i uint64, base int) []byte {
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dst, _ = formatBits(dst, i, base, false, true)
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return dst
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}
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const digits = "0123456789abcdefghijklmnopqrstuvwxyz"
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var shifts = [len(digits) + 1]uint{
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1 << 1: 1,
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1 << 2: 2,
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1 << 3: 3,
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1 << 4: 4,
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1 << 5: 5,
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}
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// formatBits computes the string representation of u in the given base.
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// If negative is set, u is treated as negative int64 value. If append_
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// is set, the string is appended to dst and the resulting byte slice is
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// returned as the first result value; otherwise the string is returned
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// as the second result value.
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//
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func formatBits(dst []byte, u uint64, base int, negative, append_ bool) (d []byte, s string) {
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if base < 2 || base > len(digits) {
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panic("invalid base")
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}
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// 2 <= base && base <= len(digits)
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var a [64 + 1]byte // +1 for sign of 64bit value in base 2
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i := len(a)
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if negative {
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u = -u
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}
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// convert bits
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if base == 10 {
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// common case: use constant 10 for / and % because
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// the compiler can optimize it into a multiply+shift
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for u >= 10 {
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i--
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a[i] = digits[u%10]
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u /= 10
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}
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} else if s := shifts[base]; s > 0 {
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// base is power of 2: use shifts and masks instead of / and %
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b := uint64(base)
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m := uintptr(b) - 1 // == 1<<s - 1
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for u >= b {
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i--
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a[i] = digits[uintptr(u)&m]
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u >>= s
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}
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} else {
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// general case
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b := uint64(base)
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for u >= b {
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i--
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a[i] = digits[u%b]
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u /= b
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}
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}
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// u < base
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i--
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a[i] = digits[uintptr(u)]
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// add sign, if any
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if negative {
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i--
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a[i] = '-'
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}
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if append_ {
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d = append(dst, a[i:]...)
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return
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}
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s = string(a[i:])
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return
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}
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