From c4c38e6364323b6d83ba3428464e19987b981d7a Mon Sep 17 00:00:00 2001 From: Szabolcs Nagy Date: Fri, 5 Feb 2021 18:48:19 +0000 Subject: 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). --- src/math/acoshf.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'src') 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; } -- cgit v1.2.1