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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
// FormatUint returns the string representation of i in the given base.
func FormatUint(i uint64, base int) string {
_, s := formatBits(nil, i, base, false, false)
return s
}
// FormatInt returns the string representation of i in the given base.
func FormatInt(i int64, base int) string {
_, s := formatBits(nil, uint64(i), base, i < 0, false)
return s
}
// Itoa is shorthand for FormatInt(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 {
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 {
dst, _ = formatBits(dst, i, base, false, true)
return dst
}
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 negative 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, negative, append_ bool) (d []byte, s string) {
if base < 2 || base > len(digits) {
panic("invalid base")
}
// 2 <= base && base <= len(digits)
var a [64 + 1]byte // +1 for sign of 64bit value in base 2
i := len(a)
if negative {
u = -u
}
// convert bits
if base == 10 {
// common case: use constant 10 for / and % because
// the compiler can optimize it into a multiply+shift
for u >= 10 {
i--
a[i] = digits[u%10]
u /= 10
}
} 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
}
} else {
// general case
b := uint64(base)
for u >= b {
i--
a[i] = digits[u%b]
u /= b
}
}
// u < base
i--
a[i] = digits[uintptr(u)]
// add sign, if any
if negative {
i--
a[i] = '-'
}
if append_ {
d = append(dst, a[i:]...)
return
}
s = string(a[i:])
return
}
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