112 lines
2.2 KiB
Go
112 lines
2.2 KiB
Go
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// 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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// TODO: use build tags once a low-level public API has been established in
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// package strconv.
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package number
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const (
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digits = "0123456789abcdefghijklmnopqrstuvwxyz"
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)
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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 neg is set, u is treated as negative int64 value. If append_ is
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// 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, neg, append_ bool) (d []byte, s string) {
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if base < 2 || base > len(digits) {
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panic("strconv: illegal AppendInt/FormatInt 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 neg {
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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 constants for / because
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// the compiler can optimize it into a multiply+shift
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if ^uintptr(0)>>32 == 0 {
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for u > uint64(^uintptr(0)) {
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q := u / 1e9
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us := uintptr(u - q*1e9) // us % 1e9 fits into a uintptr
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for j := 9; j > 0; j-- {
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i--
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qs := us / 10
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a[i] = byte(us - qs*10 + '0')
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us = qs
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}
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u = q
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}
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}
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// u guaranteed to fit into a uintptr
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us := uintptr(u)
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for us >= 10 {
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i--
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q := us / 10
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a[i] = byte(us - q*10 + '0')
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us = q
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}
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// u < 10
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i--
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a[i] = byte(us + '0')
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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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// u < base
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i--
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a[i] = digits[uintptr(u)]
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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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q := u / b
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a[i] = digits[uintptr(u-q*b)]
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u = q
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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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}
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// add sign, if any
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if neg {
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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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