tidb math 代码
文件路径：/util/mathutil/math.go
/ Copyright 2019 PingCAP, Inc.
/
/ Licensed under the Apache License, Version 2.0 (the "License");
/ you may not use this file except in compliance with the License.
/ You may obtain a copy of the License at
/
/ http://www.apache.org/licenses/LICENSE-2.0
/
/ Unless required by applicable law or agreed to in writing, software
/ distributed under the License is distributed on an "AS IS" BASIS,
/ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/ See the License for the specific language governing permissions and
/ limitations under the License.
package mathutil
import (
"math"
"golang.org/x/exp/constraints"
)
/ Architecture and/or implementation specific integer limits and bit widths.
const (
MaxInt = 1<<(IntBits-1) - 1
MinInt = -MaxInt - 1
MaxUint = 1<<IntBits - 1
IntBits = 1 << (^uint(0)>>32&1 + ^uint(0)>>16&1 + ^uint(0)>>8&1 + 3)
)
/ Abs implement the abs function according to http://cavaliercoder.com/blog/optimized-abs-for-int64-in-go.html
func Abs(n int64) int64 {
y := n >> 63
return (n ^ y) - y
}
/ uintSizeTable is used as a table to do comparison to get uint length is faster than doing loop on division with 10
var uintSizeTable = [21]uint64{
0, / redundant 0 here, so to make function StrLenOfUint64Fast to count from 1 and return i directly
9, 99, 999, 9999, 99999,
999999, 9999999, 99999999, 999999999, 9999999999,
99999999999, 999999999999, 9999999999999, 99999999999999, 999999999999999,
9999999999999999, 99999999999999999, 999999999999999999, 9999999999999999999,
math.MaxUint64,
} / math.MaxUint64 is 18446744073709551615 and it has 20 digits
/ StrLenOfUint64Fast efficiently calculate the string character lengths of an uint64 as input
func StrLenOfUint64Fast(x uint64) int {
for i := 1; ; i++ {
if x <= uintSizeTable[i] {
return i
}
}
}
/ StrLenOfInt64Fast efficiently calculate the string character lengths of an int64 as input
func StrLenOfInt64Fast(x int64) int {
size := 0
if x < 0 {
size = 1 / add "-" sign on the length count
}
return size + StrLenOfUint64Fast(uint64(Abs(x)))
}
/ IsFinite reports whether f is neither NaN nor an infinity.
func IsFinite(f float64) bool {
return !math.IsNaN(f - f)
}
/ Max returns the largest one from its arguments.
func Max[T constraints.Ordered](x T, xs ...T) T {
max := x
for _, n := range xs {
if n > max {
max = n
}
}
return max
}
/ Min returns the smallest one from its arguments.
func Min[T constraints.Ordered](x T, xs ...T) T {
min := x
for _, n := range xs {
if n < min {
min = n
}
}
return min
}
/ Clamp restrict a value to a certain interval.
func Clamp[T constraints.Ordered](n, min, max T) T {
if n >= max {
return max
} else if n <= min {
return min
}
return n
}