C library: additional floating-point functions and cleanup #8195
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tautschnig
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Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## develop #8195 +/- ##
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Coverage 79.66% 79.66%
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Files 1682 1682
Lines 195377 195377
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Hits 155641 155641
Misses 39736 39736 ☔ View full report in Codecov by Sentry. |
kroening
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Feb 8, 2024
| @@ -854,11 +899,14 @@ float sqrtf(float f) | |||
| // number of exponent and significand bits. Thus they are | |||
| // given implicitly... | |||
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| #pragma CPROVER check push | |||
| #pragma CPROVER check disable "float-overflow" | |||
| float lowerSquare = lower * lower; | |||
| __CPROVER_assume(__CPROVER_isnormalf(lowerSquare)); | |||
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A square root may well be denormal?
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I don't think that's possible for the case that f (which we are taking the square root of) is normal, which this branch assumes: given a denormal number is smaller than 1, any denormal square root s cannot be smaller than f (for f has to be denormal when s is denormal.
kroening
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Feb 8, 2024
Follows the same approximation approach as previously taken for log (and logf, logl).
We previously ended up with recursion.
Model floating-point exceptions as failing assertions.
Model fused multiply-add as documented in its man page.
We construct NaN (and Inf) by dividing by zero, which is a standards-compliant way in that Nan (Inf) is the correct result for these cases. Do not flag these operations as division-by-zero, which the user would not expect.
Fail as documented rather than via built-in assertions when overflowing.
We guess upper and lower bounds and check them for infinity afterwards. Those multiplications should not be flagged by auto-generated assertions.
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Visual Studio knows static_assert, but not the standardised _Static_assert.
Visual Studio uses `1.000000e+300 * 1.000000e+300` as value behind the `HUGE_VAL` macro. We should not report an overflow for this approach of producing infinity.
This was referenced Aug 1, 2024
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Implemented in CBMC in diffblue/cbmc#8195.
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Implemented in CBMC in diffblue/cbmc#8195. By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses. Co-authored-by: Felipe R. Monteiro <felisous@amazon.com>
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CBMC's sqrt* implementations were fixed in diffblue/cbmc#8195. By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.
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Implemented in CBMC in diffblue/cbmc#8195.
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CBMC's sqrt* implementations were fixed in diffblue/cbmc#8195.
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