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JavaScript - fastest way to negate number
4 points
In this article, we would like to show you how to negate numbers in JavaScript.
There are three ways to negate numbers:
x = -xx *= -1x = ~x + 1
x = -xoperations:- read the value from the memory
- make the value negation
- write the value to memory
x *= -1(x = x * (-1)) operations:- read the value from the memory
- make the multiplication by
-1operation - write the value to memory
x = ~x + 1operations:- read the value from the memory
- make bitwise not operation
- make add
+1operation - write the value to memory
Notes:
- multiplication operations are slower than bitwise and subtract operations,
- in this case interpreter / compliler can make some optimisation,
- amount of operations affects on performance,
- getting and setting variables from RAM memory can be slow.
The best way is always to make a benchmark test.
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// configutarion2
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var testsCount = 1;4
var testSize = 1000000;5
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// test7
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var result1 = { name: 'x = -x;', dt: 0 };9
var result2 = { name: 'x *= -1;', dt: 0 };10
var result3 = { name: 'x = ~x + 1;', dt: 0 };11
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var t1, t2;13
var x = Math.round(1000 * Math.random());14
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for (var i = 0; i < testsCount; ++i) {16
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t1 = new Date();18
for (var j = 0; j < testSize; ++j) {19
x = -x;20
}21
t2 = new Date();22
result1.dt += t2 - t1;23
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t1 = new Date();25
for (var j = 0; j < testSize; ++j) {26
x *= -1;27
}28
t2 = new Date();29
result2.dt += t2 - t1;30
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t1 = new Date();32
for (var j = 0; j < testSize; ++j) {33
x = ~x + 1;34
}35
t2 = new Date();36
result3.dt += t2 - t1;37
}38
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// summary40
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var results = [ result1, result2, result3 ];42
var max = results[0];43
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for (var i = 1; i < results.length; ++i) {45
var result = results[i];46
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if (result.dt > max.dt) {48
max = result;49
}50
}51
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console.log('x=' + x);53
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//console.log(result1.name + ' // ' + result1.dt + 'ms');55
//console.log(result2.name + ' // ' + result2.dt + 'ms');56
//console.log(result3.name + ' // ' + result3.dt + 'ms');57
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for (var i = 0; i < results.length; ++i) {59
var result = results[i];60
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if(result == max) {62
console.log(result.name + ' // ' + result.dt + 'ms');63
} else {64
var improvement = 100 * (max.dt - result.dt) / max.dt;65
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console.log( result.name 67
+ ' // ' + result.dt + 'ms' 68
+ ' -> ' + improvement.toFixed(2) + '% faster than ' + max.name);69
}70
}Note: in the above code there are 2 configuration variables:
testsCount- number of test repeats,testSize- number of iterations per one test.
This test has been made on PC with:
- OS: Windows 10 x64
- Program: NodeJS x64 v10.15.1
- CPU: Intel i5-6200u (6th generation)
- RAM: DDR4 8GB 2133 MHz
- SSD: SAMSUNG MZVLV256HCHP-00000
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# var testsCount = 1;2
# var testSize = 100000000;3
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$ node Script.js6
x=8867
x = -x; // 130ms8
x *= -1; // 114ms -> 12.31% faster than x = -x;9
x = ~x + 1; // 119ms -> 8.46% faster than x = -x;10
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$ node Script.js12
x=64313
x = -x; // 158ms14
x *= -1; // 121ms -> 23.42% faster than x = -x;15
x = ~x + 1; // 138ms -> 12.66% faster than x = -x;16
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$ node Script.js18
x=1619
x = -x; // 134ms20
x *= -1; // 117ms -> 12.69% faster than x = -x;21
x = ~x + 1; // 124ms -> 7.46% faster than x = -x;22
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$ node Script.js24
x=24125
x = -x; // 141ms26
x *= -1; // 122ms -> 13.48% faster than x = -x;27
x = ~x + 1; // 124ms -> 12.06% faster than x = -x;28
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$ node Script.js30
x=95431
x = -x; // 145ms32
x *= -1; // 117ms -> 19.31% faster than x = -x;33
x = ~x + 1; // 121ms -> 16.55% faster than x = -x;34
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$ node Script.js36
x=56937
x = -x; // 138ms38
x *= -1; // 124ms -> 10.14% faster than x = -x;39
x = ~x + 1; // 117ms -> 15.22% faster than x = -x;40
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# summary43
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x = -x; // 0 points45
x *= -1; // 5 points46
x = ~x + 1; // 1 point47
This test has been made on PC with:
- OS: Windows 10 x64
- Program: Google Chrome Version 78.0.3904.97 (Official Build) (64-bit)
- CPU: Intel i5-6200u (6th generation)
- RAM: DDR4 8GB 2133 MHz
- SSD: SAMSUNG MZVLV256HCHP-00000
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# var testsCount = 1;2
# var testSize = 100000000;3
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x=8376
x = -x; // 324ms -> 4.14% faster than x = ~x + 1;7
x *= -1; // 329ms -> 2.66% faster than x = ~x + 1;8
x = ~x + 1; // 338ms9
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x=49811
x = -x; // 326ms -> 3.26% faster than x = ~x + 1;12
x *= -1; // 323ms -> 4.15% faster than x = ~x + 1;13
x = ~x + 1; // 337ms14
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x=5916
x = -x; // 331ms -> 2.07% faster than x = ~x + 1;17
x *= -1; // 329ms -> 2.66% faster than x = ~x + 1;18
x = ~x + 1; // 338ms19
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x=51821
x = -x; // 324ms -> 5.81% faster than x = ~x + 1;22
x *= -1; // 332ms -> 3.49% faster than x = ~x + 1;23
x = ~x + 1; // 344ms24
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x=96026
x = -x; // 327ms -> 4.66% faster than x = ~x + 1;27
x *= -1; // 325ms -> 5.25% faster than x = ~x + 1;28
x = ~x + 1; // 343ms29
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x=39031
x = -x; // 336ms -> 2.61% faster than x = ~x + 1;32
x *= -1; // 335ms -> 2.90% faster than x = ~x + 1;33
x = ~x + 1; // 345ms34
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# summary37
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x = -x; // 2 points39
x *= -1; // 4 points40
x = ~x + 1; // 0 point41
This test has been made on PC with:
- OS: Windows 10 x64
- Program: Waterfox 56.2.12 (64-bit)
- CPU: Intel i5-6200u (6th generation)
- RAM: DDR4 8GB 2133 MHz
- SSD: SAMSUNG MZVLV256HCHP-00000
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# var testsCount = 1;2
# var testSize = 100000000;3
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x=9486
x = -x; // 205ms -> 14.58% faster than x = ~x + 1;7
x *= -1; // 208ms -> 13.33% faster than x = ~x + 1;8
x = ~x + 1; // 240ms9
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x=62811
x = -x; // 197ms -> 13.97% faster than x = ~x + 1;12
x *= -1; // 205ms -> 10.48% faster than x = ~x + 1;13
x = ~x + 1; // 229ms14
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x=1116
x = -x; // 199ms -> 13.85% faster than x = ~x + 1;17
x *= -1; // 205ms -> 11.26% faster than x = ~x + 1;18
x = ~x + 1; // 231ms19
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x=13421
x = -x; // 205ms -> 17.00% faster than x = ~x + 1;22
x *= -1; // 211ms -> 14.57% faster than x = ~x + 1;23
x = ~x + 1; // 247ms24
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x=24726
x = -x; // 208ms -> 13.33% faster than x = ~x + 1;27
x *= -1; // 203ms -> 15.42% faster than x = ~x + 1;28
x = ~x + 1; // 240ms29
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x=24731
x = -x; // 208ms -> 13.33% faster than x = ~x + 1;32
x *= -1; // 203ms -> 15.42% faster than x = ~x + 1;33
x = ~x + 1; // 240ms34
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# summary37
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x = -x; // 4 points39
x *= -1; // 2 points40
x = ~x + 1; // 0 point41
This test has been made on phone with:
- OS: Android 8.0.0 (MIUI Global 10.2 | Stable)
- Program: Google Chrome
- CPU: Qualcomm Snapdragon 820 8996
- RAM: 3GB
- SSD/FLASH: 60GB
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# var testsCount = 1;2
# var testSize = 100000000;3
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x=1656
x = -x; // 993ms -> 0.20% faster than x *= -1;7
x *= -1; // 995ms8
x = ~x + 1; // 882ms -> 11.36% faster than x *= -1;9
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x=63811
x = -x; // 994ms12
x *= -1; // 993ms -> 0.10% faster than x = -x;13
x = ~x + 1; // 878ms -> 11.67% faster than x = -x;14
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x=4616
x = -x; // 996ms17
x *= -1; // 992ms -> 0.40% faster than x = -x;18
x = ~x + 1; // 868ms -> 12.85% faster than x = -x;19
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x=71321
x = -x; // 1002ms22
x *= -1; // 991ms -> 1.10% faster than x = -x;23
x = ~x + 1; // 875ms -> 12.67% faster than x = -x;24
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x=25626
x = -x; // 993ms27
x *= -1; // 991ms -> 0.20% faster than x = -x;28
x = ~x + 1; // 874ms -> 11.98% faster than x = -x;29
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x=87331
x = -x; // 998ms32
x *= -1; // 991ms -> 0.70% faster than x = -x;33
x = ~x + 1; // 874ms -> 12.42% faster than x = -x;34
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# summary37
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x = -x; // 0 points39
x *= -1; // 0 points40
x = ~x + 1; // 6 point41
