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50 lines
1.7 KiB
50 lines
1.7 KiB
// 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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// See the License for the specific language governing permissions and
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// limitations under the License.
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package math
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import "math"
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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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