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| author | Szabolcs Nagy <nsz@port70.net> | 2021-02-05 18:48:19 +0000 |
|---|---|---|
| committer | Rich Felker <dalias@aerifal.cx> | 2021-02-10 14:06:36 -0500 |
| commit | c4c38e6364323b6d83ba3428464e19987b981d7a (patch) | |
| tree | 80cad290a8fd040c05a8d25df56548e13b4f7c74 | |
| parent | 074932c84d34273821e3bfc2511e60a5ce78b8d8 (diff) | |
| download | musl-c4c38e6364323b6d83ba3428464e19987b981d7a.tar.gz | |
math: fix acoshf for negative inputs
on some negative inputs (e.g. -0x1.1e6ae8p+5) acoshf failed to return
nan. ensure that negative inputs result nan without introducing new
branches. this was tried before in
commit 101e6012856918440b5d7474739c3fc22a8d3b85
math: fix acoshf on negative values
but that fix was wrong. there are 3 formulas used:
log1p(x-1 + sqrt((x-1)*(x-1)+2*(x-1)))
log(2*x - 1/(x+sqrt(x*x-1)))
log(x) + 0.693147180559945309417232121458176568
the first fails on large negative inputs (may compute log1p(0) or
log1p(inf)), the second one fails on some mid range or large negative
inputs (may compute log(large) or log(inf)) and the last one fails on
-0 (returns -inf).
| -rw-r--r-- | src/math/acoshf.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/src/math/acoshf.c b/src/math/acoshf.c index 8a4ec4d5..b773d48e 100644 --- a/src/math/acoshf.c +++ b/src/math/acoshf.c @@ -15,12 +15,12 @@ float acoshf(float x) uint32_t a = u.i & 0x7fffffff; if (a < 0x3f800000+(1<<23)) - /* |x| < 2, invalid if x < 1 or nan */ + /* |x| < 2, invalid if x < 1 */ /* up to 2ulp error in [1,1.125] */ return log1pf(x-1 + sqrtf((x-1)*(x-1)+2*(x-1))); - if (a < 0x3f800000+(12<<23)) - /* |x| < 0x1p12 */ + if (u.i < 0x3f800000+(12<<23)) + /* 2 <= x < 0x1p12 */ return logf(2*x - 1/(x+sqrtf(x*x-1))); - /* x >= 0x1p12 */ + /* x >= 0x1p12 or x <= -2 or nan */ return logf(x) + 0.693147180559945309417232121458176568f; } |