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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/tanh.c
parentcd18dc8525a275323819ac4c7826cc3404202f7b (diff)
downloadmusl-c599f4f4d705ba215a2672b92baa1c29d9dd0735.tar.gz
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/tanh.c')
-rw-r--r--src/math/tanh.c14
1 files changed, 9 insertions, 5 deletions
diff --git a/src/math/tanh.c b/src/math/tanh.c
index 0e766c5c..20d6dbcf 100644
--- a/src/math/tanh.c
+++ b/src/math/tanh.c
@@ -9,7 +9,7 @@ double tanh(double x)
union {double f; uint64_t i;} u = {.f = x};
uint32_t w;
int sign;
- double t;
+ double_t t;
/* x = |x| */
sign = u.i >> 63;
@@ -22,8 +22,7 @@ double tanh(double x)
if (w > 0x40340000) {
/* |x| > 20 or nan */
/* note: this branch avoids raising overflow */
- /* raise inexact if x!=+-inf and handle nan */
- t = 1 + 0/(x + 0x1p-120f);
+ t = 1 - 0/x;
} else {
t = expm1(2*x);
t = 1 - 2/(t+2);
@@ -32,10 +31,15 @@ double tanh(double x)
/* |x| > log(5/3)/2 ~= 0.2554 */
t = expm1(2*x);
t = t/(t+2);
- } else {
- /* |x| is small, up to 2ulp error in [0.1,0.2554] */
+ } else if (w >= 0x00100000) {
+ /* |x| >= 0x1p-1022, up to 2ulp error in [0.1,0.2554] */
t = expm1(-2*x);
t = -t/(t+2);
+ } else {
+ /* |x| is subnormal */
+ /* note: the branch above would not raise underflow in [0x1p-1023,0x1p-1022) */
+ FORCE_EVAL((float)x);
+ t = x;
}
return sign ? -t : t;
}