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Nijeesh Joshy
Nijeesh Joshy

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Why does two small for-loops run faster than a big one ?

Explain Like I am five Why does two small for loops run faster than one big for loop?

s = Date.now()
for(let i=0;i<1e10;i++) { i + 100 }
for(let i=0;i<1e10;i++) { i + 100 }
console.log(Date.now() - s)
// => 37s


s = Date.now()
for(let i=0;i<2e10;i++) { i + 100 }
console.log(Date.now() - s)
// => 38s

Especially for language like JS which is not multi-threaded

Discussion (6)

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dati profile image
da-ti

This has nothing to do with JIT compiler, loops, multi-threading or BigInt. If this was a some quiz question it would test:
-Understating that every number in js implicitly is floating point number
-Knowing how floating point addition works and that (unlike addition of integers) it takes multiple hw level operations

Addition_and_subtraction

To make this test fair for both one loop variant and two loops variant:

s = Date.now()
for(let i=0;i

Now both variants work with exact same numbers and perform exact same floating point operations (time diff is consistently <20ms on my machine now, where it was 500-1500ms before)

TLDR: floating point

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nijeesh4all profile image
Nijeesh Joshy Author • Edited on

Thanks man, it took me a while to understand. I think this might be the best answer.

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Vlastimil Pospichal

BigInt is slower.

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Nijeesh Joshy Author

i ran this in my server for more than 800 times these are my results pastebin.com/bRqku0zJ