checked_ilog: improve performance by FedericoStra · Pull Request #115913 · rust-lang/rust (original) (raw)

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Addresses #115874.

(This PR replicates the original #115875, which I accidentally closed by deleting my forked repository...)

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @joshtriplett (or someone else) soon.

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Sep 17, 2023

This was referenced

Sep 17, 2023

The implementation looks correct and we do have exhaustive tests for u16 so that part should be fine. And multiplication should be quite obviously better than division. But since you added benchmark sanyway can you add the before/after benchmark results to PR comment for future reference?

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Feb 29, 2024

I ran the benchmarks included in the fourth commit. Basically, for "before" I cherry picked just the fourth commit onto the master branch, and for the "after" I rebased the whole PR onto the master. Results below:

Before:

    num::int_log::u128_log_geometric        82.91µs/iter   +/- 1.20µs
    num::int_log::u128_log_random            2.10ms/iter   +/- 2.74µs
    num::int_log::u128_log_random_small      1.42ms/iter  +/- 14.30µs
    num::int_log::u16_log_geometric        740.00ns/iter   +/- 0.00ns
    num::int_log::u16_log_random           634.11µs/iter  +/- 10.48µs
    num::int_log::u16_log_random_small     502.78µs/iter   +/- 3.06µs
    num::int_log::u32_log_geometric          4.29µs/iter  +/- 11.00ns
    num::int_log::u32_log_random           757.75µs/iter   +/- 2.19µs
    num::int_log::u32_log_random_small     203.69µs/iter   +/- 2.36µs
    num::int_log::u64_log_geometric         26.20µs/iter +/- 124.00ns
    num::int_log::u64_log_random             1.09ms/iter   +/- 3.65µs
    num::int_log::u64_log_random_small     251.95µs/iter   +/- 3.23µs
    num::int_log::u8_log_geometric         180.00ns/iter   +/- 6.00ns
    num::int_log::u8_log_random            192.59µs/iter   +/- 2.61µs
    num::int_log::u8_log_random_small      192.83µs/iter   +/- 2.88µs

After:

    num::int_log::u128_log_geometric        26.60µs/iter  +/- 65.00ns
    num::int_log::u128_log_random            1.83ms/iter  +/- 11.76µs
    num::int_log::u128_log_random_small    936.31µs/iter   +/- 3.43µs
    num::int_log::u16_log_geometric        296.00ns/iter  +/- 17.00ns
    num::int_log::u16_log_random           466.24µs/iter   +/- 2.04µs
    num::int_log::u16_log_random_small     407.55µs/iter   +/- 9.85µs
    num::int_log::u32_log_geometric        812.00ns/iter   +/- 6.00ns
    num::int_log::u32_log_random           451.27µs/iter   +/- 2.17µs
    num::int_log::u32_log_random_small     468.65µs/iter   +/- 2.36µs
    num::int_log::u64_log_geometric          4.99µs/iter  +/- 30.00ns
    num::int_log::u64_log_random           593.27µs/iter   +/- 1.83µs
    num::int_log::u64_log_random_small     179.98µs/iter   +/- 3.62µs
    num::int_log::u8_log_geometric         129.00ns/iter   +/- 3.00ns
    num::int_log::u8_log_random            475.02µs/iter   +/- 1.58µs
    num::int_log::u8_log_random_small      474.46µs/iter   +/- 1.39µs

Looks great. Thanks.

@bors r+ rollup

📌 Commit 3de51c9 has been approved by the8472

It is now in the queue for this repository.

bors added S-waiting-on-bors

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Apr 21, 2024

bors added a commit to rust-lang-ci/rust that referenced this pull request

Apr 22, 2024

checked_ilog: improve performance

Addresses rust-lang#115874.

(This PR replicates the original rust-lang#115875, which I accidentally closed by deleting my forked repository...)

The job x86_64-gnu-aux failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

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Apr 22, 2024

Looks like a flaky test in miri, other PRs have run into that too.

@bors retry

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Apr 22, 2024

bors added a commit to rust-lang-ci/rust that referenced this pull request

Apr 22, 2024

…llaumeGomez

Rollup of 7 pull requests

Successful merges:

rust-lang#115913 (checked_ilog: improve performance)
rust-lang#124178 ([cleanup] [llvm backend] Prevent creating the same Instance::mono multiple times)
rust-lang#124183 (Stop taking ParamTy/ParamConst/EarlyParamRegion/AliasTy by ref)
rust-lang#124217 (coverage: Prepare for improved branch coverage)
rust-lang#124230 (Stabilize generic NonZero.)
rust-lang#124252 (Improve ICE message for forbidden dep-graph reads.)
rust-lang#124268 (Update books)

r? @ghost @rustbot modify labels: rollup

bors added a commit to rust-lang-ci/rust that referenced this pull request

Apr 23, 2024

…llaumeGomez

Rollup of 7 pull requests

Successful merges:

rust-lang#115913 (checked_ilog: improve performance)
rust-lang#124178 ([cleanup] [llvm backend] Prevent creating the same Instance::mono multiple times)
rust-lang#124183 (Stop taking ParamTy/ParamConst/EarlyParamRegion/AliasTy by ref)
rust-lang#124217 (coverage: Prepare for improved branch coverage)
rust-lang#124230 (Stabilize generic NonZero.)
rust-lang#124252 (Improve ICE message for forbidden dep-graph reads.)
rust-lang#124268 (Update books)

r? @ghost @rustbot modify labels: rollup

rust-timer added a commit to rust-lang-ci/rust that referenced this pull request

Apr 23, 2024

Rollup merge of rust-lang#115913 - FedericoStra:checked_ilog, r=the8472

checked_ilog: improve performance

Addresses rust-lang#115874.

(This PR replicates the original rust-lang#115875, which I accidentally closed by deleting my forked repository...)

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request

Jun 1, 2024

Unroll first iteration of checked_ilog loop

This follows the optimization of rust-lang#115913. As shown in rust-lang#115913 (comment), the performance was improved in all important cases, but some regressions were introduced for the benchmarks u32_log_random_small, u8_log_random and u8_log_random_small.

Basically, rust-lang#115913 changed the implementation from one division per iteration to one multiplication per iteration plus one division. When there are zero iterations, this is a regression from zero divisions to one division.