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authorSzabolcs Nagy <nsz@port70.net>2013-08-15 10:14:46 +0000
committerSzabolcs Nagy <nsz@port70.net>2013-08-15 10:14:46 +0000
commitc599f4f4d705ba215a2672b92baa1c29d9dd0735 (patch)
treef9931ee00f59bae9aba69b9dbcff18a5c1613018 /src/math/log1p.c
parentcd18dc8525a275323819ac4c7826cc3404202f7b (diff)
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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
Diffstat (limited to 'src/math/log1p.c')
-rw-r--r--src/math/log1p.c7
1 files changed, 5 insertions, 2 deletions
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)+ */