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| author | Szabolcs Nagy <nsz@port70.net> | 2013-10-07 18:46:43 +0000 |
|---|---|---|
| committer | Szabolcs Nagy <nsz@port70.net> | 2013-10-07 18:46:43 +0000 |
| commit | 8f438115f2c12b40fa7b1884f87db72857af67f6 (patch) | |
| tree | 2c68fb9d043c1ffe011b209a69a7a85a6e504346 /src/math/fma.c | |
| parent | 4b539a826b64d846d02a6cde9d6bcff22472af88 (diff) | |
| download | musl-8f438115f2c12b40fa7b1884f87db72857af67f6.tar.gz musl-8f438115f2c12b40fa7b1884f87db72857af67f6.tar.xz musl-8f438115f2c12b40fa7b1884f87db72857af67f6.zip | |
math: fix rare underflow issue in fma
the issue is described in commits 1e5eb73545ca6cfe8b918798835aaf6e07af5beb and ffd8ac2dd50f99c3c83d7d9d845df9874ec3e7d5
Diffstat (limited to 'src/math/fma.c')
| -rw-r--r-- | src/math/fma.c | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/src/math/fma.c b/src/math/fma.c index 84868be5..02f5c865 100644 --- a/src/math/fma.c +++ b/src/math/fma.c @@ -431,12 +431,24 @@ double fma(double x, double y, double z) /* * There is no need to worry about double rounding in directed * rounding modes. - * TODO: underflow is not raised properly, example in downward rounding: + * But underflow may not be raised properly, example in downward rounding: * fma(0x1.000000001p-1000, 0x1.000000001p-30, -0x1p-1066) */ + double ret; +#if defined(FE_INEXACT) && defined(FE_UNDERFLOW) + int e = fetestexcept(FE_INEXACT); + feclearexcept(FE_INEXACT); +#endif fesetround(oround); adj = r.lo + xy.lo; - return scalbn(r.hi + adj, spread); + ret = scalbn(r.hi + adj, spread); +#if defined(FE_INEXACT) && defined(FE_UNDERFLOW) + if (ilogb(ret) < -1022 && fetestexcept(FE_INEXACT)) + feraiseexcept(FE_UNDERFLOW); + else if (e) + feraiseexcept(FE_INEXACT); +#endif + return ret; } adj = add_adjusted(r.lo, xy.lo); |