114 lines
3.3 KiB
Go
114 lines
3.3 KiB
Go
// Copyright 2019 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package mathutil
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import (
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"cmp"
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"math"
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"github.com/pingcap/tidb/pkg/util/intest"
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"golang.org/x/exp/constraints"
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)
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// Architecture and/or implementation specific integer limits and bit widths.
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const (
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MaxInt = 1<<(IntBits-1) - 1
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MinInt = -MaxInt - 1
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MaxUint = 1<<IntBits - 1
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IntBits = 1 << (^uint(0)>>32&1 + ^uint(0)>>16&1 + ^uint(0)>>8&1 + 3)
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)
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// Abs implement the abs function according to http://cavaliercoder.com/blog/optimized-abs-for-int64-in-go.html
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func Abs(n int64) int64 {
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y := n >> 63
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return (n ^ y) - y
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}
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// uintSizeTable is used as a table to do comparison to get uint length is faster than doing loop on division with 10
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var uintSizeTable = [21]uint64{
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0, // redundant 0 here, so to make function StrLenOfUint64Fast to count from 1 and return i directly
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9, 99, 999, 9999, 99999,
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999999, 9999999, 99999999, 999999999, 9999999999,
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99999999999, 999999999999, 9999999999999, 99999999999999, 999999999999999,
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9999999999999999, 99999999999999999, 999999999999999999, 9999999999999999999,
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math.MaxUint64,
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} // math.MaxUint64 is 18446744073709551615 and it has 20 digits
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// StrLenOfUint64Fast efficiently calculate the string character lengths of an uint64 as input
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func StrLenOfUint64Fast(x uint64) int {
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for i := 1; ; i++ {
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if x <= uintSizeTable[i] {
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return i
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}
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}
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}
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// StrLenOfInt64Fast efficiently calculate the string character lengths of an int64 as input
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func StrLenOfInt64Fast(x int64) int {
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size := 0
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if x < 0 {
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size = 1 // add "-" sign on the length count
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}
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return size + StrLenOfUint64Fast(uint64(Abs(x)))
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}
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// IsFinite reports whether f is neither NaN nor an infinity.
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func IsFinite(f float64) bool {
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return !math.IsNaN(f - f)
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}
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// Clamp restrict a value to a certain interval.
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func Clamp[T cmp.Ordered](n, minv, maxv T) T {
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if n >= maxv {
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return maxv
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} else if n <= minv {
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return minv
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}
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return n
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}
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// NextPowerOfTwo returns the smallest power of two greater than or equal to `i`
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// Caller should guarantee that i > 0 and the return value is not overflow.
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func NextPowerOfTwo(i int64) int64 {
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if i&(i-1) == 0 {
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return i
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}
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i *= 2
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for i&(i-1) != 0 {
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i &= i - 1
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}
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return i
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}
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// Divide2Batches divides 'total' into 'batches'. It returns a slice of sizes
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// whose sum equals total. If total < batches, it returns total parts of size 1.
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// If total equals 0, it returns an empty slice. Batches must be > 0.
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func Divide2Batches[T constraints.Integer](total, batches T) []T {
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result := make([]T, 0, batches)
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quotient := total / batches
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remainder := total % batches
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for total > 0 {
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size := quotient
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if remainder > 0 {
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size++
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remainder--
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}
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intest.Assert(size > 0, "size should be positive")
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result = append(result, size)
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total -= size
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}
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return result
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}
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