Fix atanf spurious underflows (bug 18196).

The sysdeps/ieee754/flt-32 version of atanf produces spurious underflow exceptions for some large arguments, because of computations that compute x^-4. This patch fixes this by adjusting the threshold for large arguments (for which +/- pi/2 can just be returned, the correct result being roughly +/- pi/2 - 1/x) from 2^34 to 2^25. Tested for x86_64 and x86. [BZ #18196] * sysdeps/ieee754/flt-32/s_atanf.c (__atanf): Use 2^25 not 2^34 as threshold for large arguments. * math/auto-libm-test-in: Add another test of atan. * math/auto-libm-test-out: Regenerated.
git-mirror · May 14, 2015 · 9a71f1f · 9a71f1f
1 parent 0b7a5f9
commit 9a71f1f
Show file tree

Hide file tree

Showing 5 changed files with 35 additions and 3 deletions.
diff --git a/ChangeLog b/ChangeLog
@@ -1,5 +1,11 @@
 2015-05-14  Joseph Myers  <joseph@codesourcery.com>
 
+	[BZ #18196]
+	* sysdeps/ieee754/flt-32/s_atanf.c (__atanf): Use 2^25 not 2^34 as
+	threshold for large arguments.
+	* math/auto-libm-test-in: Add another test of atan.
+	* math/auto-libm-test-out: Regenerated.
+
 	[BZ #16339]
 	* sysdeps/i386/fpu/s_log1p.S (dbl_min): New object.
 	(__log1p): Force underflow exception for results with small

diff --git a/NEWS b/NEWS
@@ -16,8 +16,8 @@ Version 2.22
   17964, 17965, 17967, 17969, 17978, 17987, 17991, 17996, 17998, 17999,
   18007, 18019, 18020, 18029, 18030, 18032, 18036, 18038, 18039, 18042,
   18043, 18046, 18047, 18068, 18080, 18093, 18100, 18104, 18110, 18111,
-  18125, 18128, 18138, 18185, 18197, 18206, 18210, 18211, 18247, 18287,
-  18319, 18333, 18346, 18397, 18409.
+  18125, 18128, 18138, 18185, 18196, 18197, 18206, 18210, 18211, 18247,
+  18287, 18319, 18333, 18346, 18397, 18409.
 
 * Cache information can be queried via sysconf() function on s390 e.g. with
   _SC_LEVEL1_ICACHE_SIZE as argument.

diff --git a/math/auto-libm-test-in b/math/auto-libm-test-in
@@ -239,6 +239,7 @@ atan 0x1p-5
 atan 2.5
 atan 10
 atan 1e6
+atan 0x1p31
 atan 0x1p-100
 atan 0x1p-600
 atan 0x1p-10000

diff --git a/math/auto-libm-test-out b/math/auto-libm-test-out
@@ -7796,6 +7796,31 @@ atan 1e6
 = atan tonearest ldbl-128ibm 0xf.424p+16L : 0x1.921fa47d4b30ce822275563fcb8p+0L : inexact-ok
 = atan towardzero ldbl-128ibm 0xf.424p+16L : 0x1.921fa47d4b30ce822275563fcb8p+0L : inexact-ok
 = atan upward ldbl-128ibm 0xf.424p+16L : 0x1.921fa47d4b30ce822275563fccp+0L : inexact-ok
+atan 0x1p31
+= atan downward flt-32 0x8p+28f : 0x1.921fb4p+0f : inexact-ok
+= atan tonearest flt-32 0x8p+28f : 0x1.921fb6p+0f : inexact-ok
+= atan towardzero flt-32 0x8p+28f : 0x1.921fb4p+0f : inexact-ok
+= atan upward flt-32 0x8p+28f : 0x1.921fb6p+0f : inexact-ok
+= atan downward dbl-64 0x8p+28 : 0x1.921fb54242d18p+0 : inexact-ok
+= atan tonearest dbl-64 0x8p+28 : 0x1.921fb54242d18p+0 : inexact-ok
+= atan towardzero dbl-64 0x8p+28 : 0x1.921fb54242d18p+0 : inexact-ok
+= atan upward dbl-64 0x8p+28 : 0x1.921fb54242d19p+0 : inexact-ok
+= atan downward ldbl-96-intel 0x8p+28L : 0x1.921fb54242d18468p+0L : inexact-ok
+= atan tonearest ldbl-96-intel 0x8p+28L : 0x1.921fb54242d1846ap+0L : inexact-ok
+= atan towardzero ldbl-96-intel 0x8p+28L : 0x1.921fb54242d18468p+0L : inexact-ok
+= atan upward ldbl-96-intel 0x8p+28L : 0x1.921fb54242d1846ap+0L : inexact-ok
+= atan downward ldbl-96-m68k 0x8p+28L : 0x1.921fb54242d18468p+0L : inexact-ok
+= atan tonearest ldbl-96-m68k 0x8p+28L : 0x1.921fb54242d1846ap+0L : inexact-ok
+= atan towardzero ldbl-96-m68k 0x8p+28L : 0x1.921fb54242d18468p+0L : inexact-ok
+= atan upward ldbl-96-m68k 0x8p+28L : 0x1.921fb54242d1846ap+0L : inexact-ok
+= atan downward ldbl-128 0x8p+28L : 0x1.921fb54242d18469898cc519ac62p+0L : inexact-ok
+= atan tonearest ldbl-128 0x8p+28L : 0x1.921fb54242d18469898cc519ac63p+0L : inexact-ok
+= atan towardzero ldbl-128 0x8p+28L : 0x1.921fb54242d18469898cc519ac62p+0L : inexact-ok
+= atan upward ldbl-128 0x8p+28L : 0x1.921fb54242d18469898cc519ac63p+0L : inexact-ok
+= atan downward ldbl-128ibm 0x8p+28L : 0x1.921fb54242d18469898cc519acp+0L : inexact-ok
+= atan tonearest ldbl-128ibm 0x8p+28L : 0x1.921fb54242d18469898cc519ac8p+0L : inexact-ok
+= atan towardzero ldbl-128ibm 0x8p+28L : 0x1.921fb54242d18469898cc519acp+0L : inexact-ok
+= atan upward ldbl-128ibm 0x8p+28L : 0x1.921fb54242d18469898cc519ac8p+0L : inexact-ok
 atan 0x1p-100
 = atan downward flt-32 0x1p-100f : 0xf.fffffp-104f : inexact-ok
 = atan tonearest flt-32 0x1p-100f : 0x1p-100f : inexact-ok

diff --git a/sysdeps/ieee754/flt-32/s_atanf.c b/sysdeps/ieee754/flt-32/s_atanf.c
@@ -60,7 +60,7 @@ float __atanf(float x)
 
 	GET_FLOAT_WORD(hx,x);
 	ix = hx&0x7fffffff;
-	if(ix>=0x50800000) {	/* if |x| >= 2^34 */
+	if(ix>=0x4c000000) {	/* if |x| >= 2^25 */
 	    if(ix>0x7f800000)
 		return x+x;		/* NaN */
 	    if(hx>0) return  atanhi[3]+atanlo[3];