add math.wideMul #2111
Merged
add math.wideMul #2111
Conversation
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
|
This cannot do @mulWithOverflow(u128), however, on both aarch64 and x86_64 that is being done with a 4-way multiplication and just throwing away the high bits, so my case for removal still stands. |
andrewrk
reviewed
Mar 27, 2019
andrewrk
added
work in progress
andrewrk
changed the title
andrewrk
reviewed
Mar 28, 2019
| // anyway to get the carry bits. The branch on the overflow case costs more than | ||
| // just computing them unconditionally and splitting. | ||
| // | ||
| // This could be a single x86 mul instruction, which stores the carry/lower in rdx:rax. |
There was a problem hiding this comment.
Did this comment become incorrect?
There was a problem hiding this comment.
It is no longer relevant, because that is exactly what math.wideMul() does.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
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Outdated suggestions cannot be applied.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.
…mulWithOverflow
As discussed in #1350 and also std/math/big/int.zig
@mulWithOverflow() doesn't really reflect the way hardware multiply
works, or the way most architectures provide multiplication.
Also add a wideMul() that does what hardware usually provides.