BMP: Faster bitfield reading#2900
Merged
Merged
Conversation
197g
approved these changes
Apr 19, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
I noticed that BMP uses LUTs for UNORM conversions. Just like in #2899, this is not optimal for performance, so I replaced it with faster conversions using the multiply-add method.
I also made
BitField::readbranchless to hopefully allow the compiler to auto-vectorize. This also has the nice side effect that all bitfields, no matter their length, now take the same time to read, which makes performance more consistent.Here are the benchmark results from
decode.rs:As we can see, the common case of 8-bit fields (which require no conversion) is within the noise threshold (that's also what criterion said), while everything else is significantly faster.