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authorSiddhesh Poyarekar <siddhesh@sourceware.org>2016-07-18 22:33:09 +0530
committerSiddhesh Poyarekar <siddhesh@sourceware.org>2016-07-18 22:33:09 +0530
commitcbf88869edced4b23d792d95a8626e35b831df35 (patch)
treeb1ed5b36db2734e3dc0d4bcb4b6051630f7cbd0d /sysdeps/ieee754
parent2413e73c32fc36470885ae548631e081d66f4201 (diff)
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Fix cos computation for multiple precision fallback (bz #20357)
During the sincos consolidation I made two mistakes, one was a logical
error due to which cos(0x1.8475e5afd4481p+0) returned
sin(0x1.8475e5afd4481p+0) instead.

The second issue was an error in negating inputs for the correct
quadrants for sine.  I could not find a suitable test case for this
despite running a program to search for such an input for a couple of
hours.

Following patch fixes both issues.  Tested on x86_64.  Thanks to Matt
Clay for identifying the issue.

	[BZ #20357]
	* sysdeps/ieee754/dbl-64/s_sin.c (sloww): Fix up condition
	to call __mpsin/__mpcos and to negate values.
	* math/auto-libm-test-in: Add test.
	* math/auto-libm-test-out: Regenerate.
Diffstat (limited to 'sysdeps/ieee754')
-rw-r--r--sysdeps/ieee754/dbl-64/s_sin.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/sysdeps/ieee754/dbl-64/s_sin.c b/sysdeps/ieee754/dbl-64/s_sin.c
index ca2532fb63..7c9a07990f 100644
--- a/sysdeps/ieee754/dbl-64/s_sin.c
+++ b/sysdeps/ieee754/dbl-64/s_sin.c
@@ -803,7 +803,7 @@ sloww (double x, double dx, double orig, int k)
   a = t - y;
   da = ((t - a) - y) + da;
 
-  if (n == 2 || n == 1)
+  if (n & 2)
     {
       a = -a;
       da = -da;
@@ -817,7 +817,7 @@ sloww (double x, double dx, double orig, int k)
   if (w[0] == w[0] + cor)
     return (a > 0) ? w[0] : -w[0];
 
-  return (n & 1) ? __mpcos (orig, 0, true) : __mpsin (orig, 0, true);
+  return k ? __mpcos (orig, 0, true) : __mpsin (orig, 0, true);
 }
 
 /***************************************************************************/