From f4d9bfb3a986f2c25ec023426b4fb222130af75f Mon Sep 17 00:00:00 2001 From: Szabolcs Nagy Date: Thu, 5 Sep 2013 16:57:46 +0000 Subject: math: fix atanh (overflow and underflow issues) in atanh exception handling was left to the called log functions, but the argument to those functions could underflow or overflow. use double_t and float_t to avoid some useless stores on x86 --- src/math/atanh.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) (limited to 'src/math/atanh.c') diff --git a/src/math/atanh.c b/src/math/atanh.c index 84a84c69..63a035d7 100644 --- a/src/math/atanh.c +++ b/src/math/atanh.c @@ -6,16 +6,24 @@ double atanh(double x) union {double f; uint64_t i;} u = {.f = x}; unsigned e = u.i >> 52 & 0x7ff; unsigned s = u.i >> 63; + double_t y; /* |x| */ u.i &= (uint64_t)-1/2; - x = u.f; + y = u.f; if (e < 0x3ff - 1) { - /* |x| < 0.5, up to 1.7ulp error */ - x = 0.5*log1p(2*x + 2*x*x/(1-x)); + if (e < 0x3ff - 32) { + /* handle underflow */ + if (e == 0) + FORCE_EVAL((float)y); + } else { + /* |x| < 0.5, up to 1.7ulp error */ + y = 0.5*log1p(2*y + 2*y*y/(1-y)); + } } else { - x = 0.5*log1p(2*x/(1-x)); + /* avoid overflow */ + y = 0.5*log1p(2*(y/(1-y))); } - return s ? -x : x; + return s ? -y : y; } -- cgit v1.2.1