Change implementation of fnearest() #504
Merged
Conversation
This file contains 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
axic
reviewed
Aug 23, 2020
axic
reviewed
Aug 23, 2020
lib/fizzy/execute.cpp
Outdated
|
|
||
| return result; | ||
| const auto t = std::trunc(value); | ||
| if (const auto diff = std::abs(value - t); diff > 0.5f || (diff == 0.5f && !is_even(t))) |
There was a problem hiding this comment.
Wouldn't it be less branching to have two if cases than using abs? Or is abs constexpr and the compiler can optimise all this out?
There was a problem hiding this comment.
The abs (or fabs in C) is recognized and replaced with __builtin_abs or something. This just masks out the sign bit: x & 0x7fffffff.
Codecov Report
@@ Coverage Diff @@
## master #504 +/- ##
==========================================
- Coverage 99.69% 99.69% -0.01%
==========================================
Files 54 54
Lines 17198 17180 -18
==========================================
- Hits 17146 17128 -18
Misses 52 52 |
|
I also have another implementation based on bit manipulation which looks to be faster but I did not perform proper benchmarks yet. We may wait with that for the next release until having more FP test cases. |
gumb0
reviewed
Sep 1, 2020
chfast
force-pushed
the
better_nearest
branch
from
05b277f
to
2f9edfe
Compare
axic
reviewed
Sep 2, 2020
chfast
force-pushed
the
better_nearest
branch
from
2f9edfe
to
db4421c
Compare
gumb0
approved these changes
Sep 2, 2020
|
I'm checking some additional options because there are some performance regressions. |
This implementation does not need to modify rounding direction to work correctly under any rounding direction.
chfast
force-pushed
the
better_nearest
branch
from
4e072bd
to
c413a4c
Compare
|
GCC: GCC+LTO: So not really significant difference (none of the benchmarks uses this instruction). The change is not driven by performance anyway. When marking the function with |
chfast
force-pushed
the
better_nearest
branch
from
c413a4c
to
4e42e95
Compare
axic
approved these changes
Sep 2, 2020
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.
This implementation does not need to modify rounding direction to work
correctly under any rounding direction.