std.math: Implement more optimal floorImpl for ieeeSingle #5820
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Thanks for your pull request, @ibuclaw! Bugzilla referencesYour PR doesn't reference any Bugzilla issue. If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog. Testing this PR locallyIf you don't have a local development environment setup, you can use Digger to test this PR: dub fetch digger
dub run digger -- build "master + phobos#5820" |
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Ping? |
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Pinging people who are qualified to review this from git blame @yebblies @wilzbach @don-clugston-sociomantic @klickverbot |
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Or you know, you could just request a review. :) |
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| // Other kinds of extractors for real formats. | ||
| static if (F.realFormat == RealFormat.ieeeSingle) | ||
| int vi; | ||
| } | ||
| floatBits y = void; | ||
| y.rv = x; | ||
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| // Find the exponent (power of 2) |
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This deserves a much better comment since this code is actually quite tricky.
// Find the exponent (power of 2)
// Do this by shifting the raw value so that the exponent lies in the low bits.
// Then mask out the sign bit, and subtract the bias
std/math.d
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| exp -= 16; | ||
| if (exp < (T.mant_dig - 1)) | ||
| { | ||
| const uint i = F.MANTISSAMASK_INT >> exp; |
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This variable deserves a better name. I think this is actually fraction_mask, the bits of the mantissa which form the fraction.
std/math.d
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| if ((y.vi & i) != 0) | ||
| { | ||
| if (y.vi < 0) | ||
| y.vi += 0x00800000 >> exp; |
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This REALLY needs a comment. My guess is that this is the float value 0.5, added so that it rounds up towards zero? Or something like that.
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This is subtracting one, adding comment.
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@redstar - And this you might be interested in also. |
Less branching, and doesn't care about endian-ness. Tested against PPC64/LE.
For comparison between old (source view 1) and new (source view 2) https://explore.dgnu.org/g/fTvttz
Probably better to review with https://github.com/dlang/phobos/pull/5820/files?w=1