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Diffstat (limited to '')
| -rw-r--r-- | src/strconv/itoa.go | 206 |
1 files changed, 206 insertions, 0 deletions
diff --git a/src/strconv/itoa.go b/src/strconv/itoa.go new file mode 100644 index 0000000..45e4192 --- /dev/null +++ b/src/strconv/itoa.go @@ -0,0 +1,206 @@ +// 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 +} |