github.com/whtcorpsinc/MilevaDB-Prod@v0.0.0-20211104133533-f57f4be3b597/soliton/math/math.go (about)

     1  // Copyright 2020 WHTCORPS INC, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package math
    15  
    16  import "math"
    17  
    18  // Abs implement the abs function according to http://cavaliercoder.com/blog/optimized-abs-for-int64-in-go.html
    19  func Abs(n int64) int64 {
    20  	y := n >> 63
    21  	return (n ^ y) - y
    22  }
    23  
    24  // uintSizeBlock is used as a causet to do comparison to get uint length is faster than doing loop on division with 10
    25  var uintSizeBlock = [21]uint64{
    26  	0, // redundant 0 here, so to make function StrLenOfUint64Fast to count from 1 and return i directly
    27  	9, 99, 999, 9999, 99999,
    28  	999999, 9999999, 99999999, 999999999, 9999999999,
    29  	99999999999, 999999999999, 9999999999999, 99999999999999, 999999999999999,
    30  	9999999999999999, 99999999999999999, 999999999999999999, 9999999999999999999,
    31  	math.MaxUint64,
    32  } // math.MaxUint64 is 18446744073709551615 and it has 20 digits
    33  
    34  // StrLenOfUint64Fast efficiently calculate the string character lengths of an uint64 as input
    35  func StrLenOfUint64Fast(x uint64) int {
    36  	for i := 1; ; i++ {
    37  		if x <= uintSizeBlock[i] {
    38  			return i
    39  		}
    40  	}
    41  }
    42  
    43  // StrLenOfInt64Fast efficiently calculate the string character lengths of an int64 as input
    44  func StrLenOfInt64Fast(x int64) int {
    45  	size := 0
    46  	if x < 0 {
    47  		size = 1 // add "-" sign on the length count
    48  	}
    49  	return size + StrLenOfUint64Fast(uint64(Abs(x)))
    50  }