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charset.go
173 lines (150 loc) · 4.08 KB
/
charset.go
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package tools
import (
"math/bits"
)
const nSmalls = 100
const smallsString = "00010203040506070809" +
"10111213141516171819" +
"20212223242526272829" +
"30313233343536373839" +
"40414243444546474849" +
"50515253545556575859" +
"60616263646566676869" +
"70717273747576777879" +
"80818283848586878889" +
"90919293949596979899"
const host32bit = ^uint(0)>>32 == 0
const fastSmalls = true // enable fast path for small integers
const digits = "0123456789abcdefghijklmnopqrstuvwxyz"
// Float 此结构体用来进行自定义的Str拼接类型转换
type Float struct {
Number any
Fmt byte
Pre int
}
// 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, byt *[]byte) int {
if fastSmalls && 0 <= i && i < nSmalls && base == 10 {
if i < 10 {
*byt = append(*byt, digits[i : i+1][0])
return 1
} else {
*byt = append(*byt, []byte(smallsString[i*2:i*2+2])...)
return 2
}
}
return formatBits(byt, uint64(i), base, i < 0)
}
// appendInt is quick append int to String
func appendInt(i int, byt *[]byte) int {
return formatInt(int64(i), 10, byt)
}
func formatBits(dst *[]byte, u uint64, base int, neg bool) int {
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] = '-'
}
*dst = append(*dst, a[i:]...)
return len(a[i:])
}
func isPowerOfTwo(x int) bool {
return x&(x-1) == 0
}
// AppendUint appends the string form of the unsigned integer i,
// as generated by FormatUint, to dst and returns the extended buffer.
func appendUint64(i uint64, byt *[]byte) int {
return formatBits(byt, i, 10, i < 0)
}