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| author | Szabolcs Nagy <nsz@port70.net> | 2020-01-20 20:38:45 +0000 |
|---|---|---|
| committer | Rich Felker <dalias@aerifal.cx> | 2020-02-21 23:42:12 -0500 |
| commit | d20558148d8a2c52229b02668627697e83ca3840 (patch) | |
| tree | e4f3373bb8649db621bfeb871ed335e13886b343 /src/math/__expo2.c | |
| parent | b3797d3b2e10e6fff2a6b04af917e61e95838b08 (diff) | |
| download | musl-d20558148d8a2c52229b02668627697e83ca3840.tar.gz | |
math: fix sinh overflows in non-nearest rounding
The final rounding operation should be done with the correct sign
otherwise huge results may incorrectly get rounded to or away from
infinity in upward or downward rounding modes.
This affected sinh and sinhf which set the sign on the result after
a potentially overflowing mul. There may be other non-nearest rounding
issues, but this was a known long standing issue with large ulp error
(depending on how ulp is defined near infinity).
The fix should have no effect on sinh and sinhf performance but may
have a tiny effect on cosh and coshf.
Diffstat (limited to 'src/math/__expo2.c')
| -rw-r--r-- | src/math/__expo2.c | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/src/math/__expo2.c b/src/math/__expo2.c index 740ac680..248f052b 100644 --- a/src/math/__expo2.c +++ b/src/math/__expo2.c @@ -5,12 +5,13 @@ static const int k = 2043; static const double kln2 = 0x1.62066151add8bp+10; /* exp(x)/2 for x >= log(DBL_MAX), slightly better than 0.5*exp(x/2)*exp(x/2) */ -double __expo2(double x) +double __expo2(double x, double sign) { double scale; /* note that k is odd and scale*scale overflows */ INSERT_WORDS(scale, (uint32_t)(0x3ff + k/2) << 20, 0); /* exp(x - k ln2) * 2**(k-1) */ - return exp(x - kln2) * scale * scale; + /* in directed rounding correct sign before rounding or overflow is important */ + return exp(x - kln2) * (sign * scale) * scale; } |