Add Average trait with integer average computation #31
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Outdated suggestions cannot be applied.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.
This is actually a copy of #20, I had to reopen a PR to address the fixes as I deleted the repository in between
Hi there !
This PR adds a new trait Average with two methods Average.average_ceil and Average.average_floor that uses bitwise operations to compute the average of two integers without overflowing. Reference is here, but this is probably known to people thanks to the Hacker's Delight.
Basically:
⌊(x+y)/2⌋ = (x&y) + ((x^y) >> 1)
⌈(x+y)/2⌉ = (x|y) - ((x^y) >> 1)
It comes with a blanket implementation for all Integer implementors that are closed under the -+|&^>> operators; in particular, this blanket implementation works for the BigInt and BigUint structs.
In terms of performance, this implementation is about 1.5 times faster than a naive implementation that checks for overflow, and as fast as an implementation that doesn't (i.e. (x+y)/2).
I'll add more tests for the std primitives, please do tell me if anything else needs to be changed.