Add "integer square root" method to integer primitive types #116176

FedericoStra · 2023-09-26T14:29:05Z

For every suffix N among 8, 16, 32, 64, 128 and size, this PR adds the methods

const fn uN::isqrt() -> uN;
const fn iN::isqrt() -> iN;
const fn iN::checked_isqrt() -> Option<iN>;

to compute the integer square root, addressing issue #89273.

The implementation is based on the base 2 digit-by-digit algorithm on Wikipedia, which after some benchmarking has proved to be faster than both binary search and Heron's/Newton's method. I haven't had the time to understand and port this code based on lookup tables instead, but I'm not sure whether it's worth complicating such a function this much for relatively little benefit.

rustbot · 2023-09-26T14:29:13Z

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

Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (S-waiting-on-review and S-waiting-on-author) stays updated, invoking these commands when appropriate:

@rustbot author: the review is finished, PR author should check the comments and take action accordingly
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joboet

Looks great to me, except for some small nits. Also, could you file an API change proposal for this method? That will allow separating discussions about the API from the implementation review.

@rustbot label +T-libs-api +S-waiting-on-ACP

library/core/src/num/int_macros.rs

library/core/src/num/uint_macros.rs

cuviper · 2023-09-26T16:49:25Z

r? libs-api

library/core/src/num/uint_macros.rs

dtolnay · 2023-09-28T00:31:50Z

This API looks good to me. I'd be all right landing this without ACP. But if you already have one in progress, feel free to post and I'll approve it.

Please open a tracking issue using the Library Tracking Issue template (https://github.com/rust-lang/rust/issues/new/choose) and update the stability attribute as shown in #116176 (comment).

Fix C-ism and type inference.

FedericoStra · 2023-09-28T10:54:03Z

This API looks good to me. I'd be all right landing this without ACP. But if you already have one in progress, feel free to post and I'll approve it.

I'm not familiar with the ACP procedure (first time contributing) and I don't have one ready yet; however if you change idea and want me to create one I'll try to produce something decent.

Please open a tracking issue using the Library Tracking Issue template (https://github.com/rust-lang/rust/issues/new/choose) and update the stability attribute as shown in #116176 (comment).

I've opened the tracking issue #116226 and marked the methods as

#[unstable(feature = "isqrt", issue = "116226")]
#[rustc_const_unstable(feature = "isqrt", issue = "116226")]

rust-lang#89273 (comment)

library/core/tests/num/int_macros.rs

dtolnay

Thanks!

dtolnay · 2023-09-28T16:14:23Z

@bors r+

bors · 2023-09-28T16:14:25Z

📌 Commit 25648de has been approved by dtolnay

It is now in the queue for this repository.

bors · 2023-09-28T19:40:43Z

⌛ Testing commit 25648de with merge 7defbf2...

Add "integer square root" method to integer primitive types For every suffix `N` among `8`, `16`, `32`, `64`, `128` and `size`, this PR adds the methods ```rust const fn uN::isqrt() -> uN; const fn iN::isqrt() -> iN; const fn iN::checked_isqrt() -> Option<iN>; ``` to compute the [integer square root](https://en.wikipedia.org/wiki/Integer_square_root), addressing issue rust-lang#89273. The implementation is based on the [base 2 digit-by-digit algorithm](https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Binary_numeral_system_(base_2)) on Wikipedia, which after some benchmarking has proved to be faster than both binary search and Heron's/Newton's method. I haven't had the time to understand and port [this code](http://atoms.alife.co.uk/sqrt/SquareRoot.java) based on lookup tables instead, but I'm not sure whether it's worth complicating such a function this much for relatively little benefit.

bors · 2023-09-28T19:43:10Z

💔 Test failed - checks-actions

rust-log-analyzer · 2023-09-28T20:11:51Z

A job failed! Check out the build log: (web) (plain)

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


Sending build context to Docker daemon  432.1kB

Step 1/14 : FROM ubuntu:22.04
Head "https://registry-1.docker.io/v2/library/ubuntu/manifests/22.04": EOF
DEPRECATED: The legacy builder is deprecated and will be removed in a future release.
            BuildKit is currently disabled; enable it by removing the DOCKER_BUILDKIT=0
            environment-variable.


Sending build context to Docker daemon  432.1kB

Step 1/14 : FROM ubuntu:22.04
Head "https://registry-1.docker.io/v2/library/ubuntu/manifests/22.04": Get "https://auth.docker.io/token?account=githubactions&scope=repository%3Alibrary%2Fubuntu%3Apull&service=registry.docker.io": EOF
DEPRECATED: The legacy builder is deprecated and will be removed in a future release.
            BuildKit is currently disabled; enable it by removing the DOCKER_BUILDKIT=0
            environment-variable.


Sending build context to Docker daemon  432.1kB

Step 1/14 : FROM ubuntu:22.04
Head "https://registry-1.docker.io/v2/library/ubuntu/manifests/22.04": Get "https://auth.docker.io/token?account=githubactions&scope=repository%3Alibrary%2Fubuntu%3Apull&service=registry.docker.io": EOF
DEPRECATED: The legacy builder is deprecated and will be removed in a future release.
            BuildKit is currently disabled; enable it by removing the DOCKER_BUILDKIT=0
            environment-variable.


Sending build context to Docker daemon  432.1kB

Step 1/14 : FROM ubuntu:22.04
Get "https://registry-1.docker.io/v2/": EOF
DEPRECATED: The legacy builder is deprecated and will be removed in a future release.
            BuildKit is currently disabled; enable it by removing the DOCKER_BUILDKIT=0
            environment-variable.


Sending build context to Docker daemon  432.1kB

Step 1/14 : FROM ubuntu:22.04
Get "https://registry-1.docker.io/v2/": EOF
##[error]Process completed with exit code 1.
Post job cleanup.

dtolnay · 2023-09-28T20:14:17Z

  Get "https://registry-1.docker.io/v2/": EOF
  The command has failed after 5 attempts.

Looks like a flake.

@bors retry

bors · 2023-09-29T07:35:48Z

⌛ Testing commit 25648de with merge b8536c1...

bors · 2023-09-29T09:23:25Z

☀️ Test successful - checks-actions
Approved by: dtolnay
Pushing b8536c1 to master...

rust-timer · 2023-09-29T10:44:33Z

Finished benchmarking commit (b8536c1): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.6%	[0.4%, 0.7%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.1%	[2.1%, 2.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 632.014s -> 631.581s (-0.07%)
Artifact size: 317.22 MiB -> 317.22 MiB (0.00%)

FedericoStra added 4 commits September 22, 2023 16:11

isqrt: initial implementation

3e8676c

isqrt: add tests

1b34f1c

isqrt: remove duplication by delegating to unsigned integers

68f0b47

isqrt: add more tests

d49da0f

rustbot assigned cuviper Sep 26, 2023

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Sep 26, 2023

joboet requested changes Sep 26, 2023

View reviewed changes

rustbot added S-waiting-on-ACP Status: PR has an ACP and is waiting for the ACP to complete. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. labels Sep 26, 2023

rustbot assigned dtolnay and unassigned cuviper Sep 26, 2023

dtolnay reviewed Sep 28, 2023

View reviewed changes

library/core/src/num/uint_macros.rs Show resolved Hide resolved

FedericoStra added 3 commits September 28, 2023 11:39

fixup! isqrt: initial implementation

17dfb18

Fix C-ism and type inference.

isqrt: fix stability

c97ab23

isqrt: cite source and rename variables to match original C code

5146317

FedericoStra mentioned this pull request Sep 28, 2023

Tracking Issue for {u8,i8,...}::isqrt #116226

Closed

3 tasks

fixup! isqrt: fix stability

77f9eae

isqrt: assume that isqrt takes half as many bits

fcdfd5b

rust-lang#89273 (comment)

dtolnay requested changes Sep 28, 2023

View reviewed changes

library/core/tests/num/int_macros.rs Outdated Show resolved Hide resolved

isqrt: disable long running tests in Miri

25648de

FedericoStra requested a review from dtolnay September 28, 2023 16:01

dtolnay approved these changes Sep 28, 2023

View reviewed changes

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Sep 28, 2023

bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Sep 28, 2023

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 28, 2023

bors added the merged-by-bors This PR was explicitly merged by bors. label Sep 29, 2023

bors merged commit b8536c1 into rust-lang:master Sep 29, 2023
12 checks passed

rustbot added this to the 1.74.0 milestone Sep 29, 2023

bors mentioned this pull request Sep 29, 2023

Implement strict integer operations that panic on overflow #116090

Merged

pvdrz mentioned this pull request Oct 4, 2023

Fix divergence from upstream master ferrocene/ferrocene#23

Merged

ChaiTRex mentioned this pull request Aug 31, 2024

FCP WIP ChaiTRex/rust#1

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Add "integer square root" method to integer primitive types #116176

Add "integer square root" method to integer primitive types #116176

FedericoStra commented Sep 26, 2023 •

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dtolnay commented Sep 28, 2023

bors commented Sep 29, 2023

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rust-timer commented Sep 29, 2023

Add "integer square root" method to integer primitive types #116176

Add "integer square root" method to integer primitive types #116176

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rust-timer commented Sep 29, 2023

Overall result: ❌ regressions - no action needed

Instruction count

Max RSS (memory usage)

Cycles

Binary size

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