From c599f4f4d705ba215a2672b92baa1c29d9dd0735 Mon Sep 17 00:00:00 2001 From: Szabolcs Nagy Date: Thu, 15 Aug 2013 10:14:46 +0000 Subject: math: fix asin, atan, log1p, tanh to raise underflow on subnormal for these functions f(x)=x for small inputs, because f(0)=0 and f'(0)=1, but for subnormal values they should raise the underflow flag (required by annex F), if they are approximated by a polynomial around 0 then spurious underflow should be avoided (not required by annex F) all these functions should raise inexact flag for small x if x!=0, but it's not required by the standard and it does not seem a worthy goal, so support for it is removed in some cases. raising underflow: - x*x may not raise underflow for subnormal x if FLT_EVAL_METHOD!=0 - x*x may raise spurious underflow for normal x if FLT_EVAL_METHOD==0 - in case of double subnormal x, store x as float - in case of float subnormal x, store x*x as float --- src/math/log1p.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'src/math/log1p.c') diff --git a/src/math/log1p.c b/src/math/log1p.c index 6c67249c..9bed63c2 100644 --- a/src/math/log1p.c +++ b/src/math/log1p.c @@ -104,9 +104,12 @@ double log1p(double x) return (x-x)/(x-x); /* log1p(x<-1)=NaN */ } if (ax < 0x3e200000) { /* |x| < 2**-29 */ - /* raise inexact */ - if (two54 + x > 0.0 && ax < 0x3c900000) /* |x| < 2**-54 */ + /* if 0x1p-1022 <= |x| < 0x1p-54, avoid raising underflow */ + if (ax < 0x3c900000 && ax >= 0x00100000) return x; +#if FLT_EVAL_METHOD != 0 + FORCE_EVAL((float)x); +#endif return x - x*x*0.5; } if (hx > 0 || hx <= (int32_t)0xbfd2bec4) { /* sqrt(2)/2- <= 1+x < sqrt(2)+ */ -- cgit v1.2.1