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authorJoseph Myers <joseph@codesourcery.com>2015-05-15 17:47:29 +0000
committerJoseph Myers <joseph@codesourcery.com>2015-05-15 17:47:29 +0000
commit5a608ccc2d676aa124f6b55a7b20d071e408ca31 (patch)
tree41c40103e1b049d25bc519ca0688f48d82d61656 /sysdeps/ieee754
parentff069f024ae8cf15d53429e034d67ddcece0f67a (diff)
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Fix tanf spurious underflows (bug 18221).
The flt-32 implementation of tanf produces spurious underflow
exceptions for some small arguments, through computing values on the
order of x^5.  This patch fixes this by adjusting the threshold for
returning x (or, as applicable, +/- 1/x) to 2**-13 (the next term in
the power series being x^3/3).

Tested for x86_64 and x86.

	[BZ #18221]
	* sysdeps/ieee754/flt-32/k_tanf.c (__kernel_tanf): Use 2**-13 not
	2**-28 as threshold for returning x or +/- 1/x.
	* math/auto-libm-test-in: Add more tests of tan.
	* math/auto-libm-test-out: Regenerated.
Diffstat (limited to 'sysdeps/ieee754')
-rw-r--r--sysdeps/ieee754/flt-32/k_tanf.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/sysdeps/ieee754/flt-32/k_tanf.c b/sysdeps/ieee754/flt-32/k_tanf.c
index d918826338..a67f36e283 100644
--- a/sysdeps/ieee754/flt-32/k_tanf.c
+++ b/sysdeps/ieee754/flt-32/k_tanf.c
@@ -45,7 +45,7 @@ float __kernel_tanf(float x, float y, int iy)
 	int32_t ix,hx;
 	GET_FLOAT_WORD(hx,x);
 	ix = hx&0x7fffffff;	/* high word of |x| */
-	if(ix<0x31800000)			/* x < 2**-28 */
+	if(ix<0x39000000)			/* x < 2**-13 */
 	    {if((int)x==0) {			/* generate inexact */
 		if((ix|(iy+1))==0) return one/fabsf(x);
 		else return (iy==1)? x: -one/x;