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math: add fma TODO comments about the underflow issue

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The underflow exception is not raised correctly in some
cornercases (see previous fma commit), added comments
with examples for fmaf, fmal and non-x86 fma.

In fmaf store the result before returning so it has the
correct precision when FLT_EVAL_METHOD!=0
This commit is contained in:
Szabolcs Nagy 2013-05-19 14:43:32 +00:00
commit 1e5eb73545
3 changed files with 14 additions and 2 deletions
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src/math/fmal.c
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@ -262,6 +262,8 @@ 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:
* fmal(0x1.0000000001p-16000L, 0x1.0000000001p-400L, -0x1p-16440L)
*/
fesetround(oround);
adj = r.lo + xy.lo;