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authorSzabolcs Nagy <nsz@port70.net>2013-10-07 18:46:43 +0000
committerSzabolcs Nagy <nsz@port70.net>2013-10-07 18:46:43 +0000
commit8f438115f2c12b40fa7b1884f87db72857af67f6 (patch)
tree2c68fb9d043c1ffe011b209a69a7a85a6e504346 /src/math/fmal.c
parent4b539a826b64d846d02a6cde9d6bcff22472af88 (diff)
downloadmusl-8f438115f2c12b40fa7b1884f87db72857af67f6.tar.gz
math: fix rare underflow issue in fma
the issue is described in commits 1e5eb73545ca6cfe8b918798835aaf6e07af5beb and ffd8ac2dd50f99c3c83d7d9d845df9874ec3e7d5
Diffstat (limited to 'src/math/fmal.c')
-rw-r--r--src/math/fmal.c16
1 files changed, 14 insertions, 2 deletions
diff --git a/src/math/fmal.c b/src/math/fmal.c
index c68db255..4506aac6 100644
--- a/src/math/fmal.c
+++ b/src/math/fmal.c
@@ -264,12 +264,24 @@ long double fmal(long double x, long double y, long double z)
/*
* There is no need to worry about double rounding in directed
* rounding modes.
- * TODO: underflow is not raised correctly, example in downward rounding:
+ * But underflow may not be raised correctly, example in downward rounding:
* fmal(0x1.0000000001p-16000L, 0x1.0000000001p-400L, -0x1p-16440L)
*/
+ long 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 scalbnl(r.hi + adj, spread);
+ ret = scalbnl(r.hi + adj, spread);
+#if defined(FE_INEXACT) && defined(FE_UNDERFLOW)
+ if (ilogbl(ret) < -16382 && fetestexcept(FE_INEXACT))
+ feraiseexcept(FE_UNDERFLOW);
+ else if (e)
+ feraiseexcept(FE_INEXACT);
+#endif
+ return ret;
}
adj = add_adjusted(r.lo, xy.lo);