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/asin.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
(limited to 'src/math/asin.c')
diff --git a/src/math/asin.c b/src/math/asin.c
index 3e8f99ed..c926b188 100644
--- a/src/math/asin.c
+++ b/src/math/asin.c
@@ -82,11 +82,9 @@ double asin(double x)
}
/* |x| < 0.5 */
if (ix < 0x3fe00000) {
- if (ix < 0x3e500000) {
- /* |x|<0x1p-26, return x with inexact if x!=0*/
- FORCE_EVAL(x + 0x1p120f);
+ /* if 0x1p-1022 <= |x| < 0x1p-26, avoid raising underflow */
+ if (ix < 0x3e500000 && ix >= 0x00100000)
return x;
- }
return x + x*R(x*x);
}
/* 1 > |x| >= 0.5 */
--
cgit v1.2.1