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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.
// TODO: use build tags once a low-level public API has been established in
// package strconv.
package number
const (
digits = "0123456789abcdefghijklmnopqrstuvwxyz"
)
var shifts = [len(digits) + 1]uint{
1 << 1: 1,
1 << 2: 2,
1 << 3: 3,
1 << 4: 4,
1 << 5: 5,
}
// 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
if base == 10 {
// common case: use constants for / because
// the compiler can optimize it into a multiply+shift
if ^uintptr(0)>>32 == 0 {
for u > uint64(^uintptr(0)) {
q := u / 1e9
us := uintptr(u - q*1e9) // us % 1e9 fits into a uintptr
for j := 9; j > 0; j-- {
i--
qs := us / 10
a[i] = byte(us - qs*10 + '0')
us = qs
}
u = q
}
}
// u guaranteed to fit into a uintptr
us := uintptr(u)
for us >= 10 {
i--
q := us / 10
a[i] = byte(us - q*10 + '0')
us = q
}
// u < 10
i--
a[i] = byte(us + '0')
} else if s := shifts[base]; s > 0 {
// base is power of 2: use shifts and masks instead of / and %
b := uint64(base)
m := uintptr(b) - 1 // == 1<<s - 1
for u >= b {
i--
a[i] = digits[uintptr(u)&m]
u >>= s
}
// u < base
i--
a[i] = digits[uintptr(u)]
} else {
// general case
b := uint64(base)
for u >= b {
i--
q := u / b
a[i] = digits[uintptr(u-q*b)]
u = q
}
// u < base
i--
a[i] = digits[uintptr(u)]
}
// add sign, if any
if neg {
i--
a[i] = '-'
}
if append_ {
d = append(dst, a[i:]...)
return
}
s = string(a[i:])
return
}
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