Optimize divisions and remainders by constants. #5167

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sjrd wants to merge 1 commit into scala-js:main from sjrd:opt-divide-and-remainder

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sjrd commented May 10, 2025 •

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Following the techniques described in Hacker's Delight, Chapter 10.

Benchmarking suggested that is this generally worth it, except for non-powers of 2 for a) int operations on JS and b) long operations on Wasm.

For the long divisions on JS, this yields a 6x speedup, despite the fact that the resulting code needs 16 (!) primitive int multiplications.

sjrd force-pushed the opt-divide-and-remainder branch 2 times, most recently from b0ca504 to 0ef8849 Compare

June 2, 2025 15:34

sjrd force-pushed the opt-divide-and-remainder branch from 0ef8849 to 560a48c Compare

June 13, 2025 16:38

sjrd force-pushed the opt-divide-and-remainder branch 3 times, most recently from eee96e7 to 864ebae Compare

June 23, 2025 15:23

sjrd force-pushed the opt-divide-and-remainder branch 4 times, most recently from 3eac5c3 to 615ec6a Compare

July 15, 2025 15:24

sjrd marked this pull request as ready for review

July 15, 2025 15:25

sjrd requested a review from gzm0

July 15, 2025 15:25

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sjrd commented Jul 15, 2025

@gzm0 This PR is now ready for review. It sent me through many detours before I could finish it. :p

sjrd force-pushed the opt-divide-and-remainder branch 4 times, most recently from 95a590f to be78b6a Compare

July 15, 2025 16:43


          Optimize divisions and remainders by constants.

04771e4

Following the techniques described in Hacker's Delight, Chapter 10.

Benchmarking suggested that is this generally worth it, except for
non-powers of 2 for a) int operations on JS and b) long operations
on Wasm.

For the long divisions on JS, this yields a 6x speedup, despite the
fact that the resulting code needs 16 (!) primitive int
multiplications.

sjrd force-pushed the opt-divide-and-remainder branch from be78b6a to 04771e4 Compare

July 25, 2025 08:49

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