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Check n instead of k1 to decide on sign of sin/cos result

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For k1 in 1 and 3, n can only have values of 0 and 2, so checking k1 &
2 is equivalent to checking n & 2.  We prefer the latter so that we
don't use k1 for anything other than selecting the quadrant in
do_sincos_1, thus dropping it completely.

The previous logic was:

    "Compute sine for the value and based on the new rotated quadrant
     (k1) negate the value if we're in the fourth quadrant."

With this change, the logic now is:

    "Compute sine for the value and negate it if we were either (1) in
     the fourth quadrant or (2) we actually wanted the cosine and were
     in the third quadrant."

	* sysdeps/ieee754/dbl-64/s_sin.c (do_sincos_1): Check N
	instead of K1.
This commit is contained in:
Siddhesh Poyarekar 2016-10-06 00:34:26 +05:30
parent b8b7e5e644
commit ba4e688461
2 changed files with 4 additions and 1 deletions
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3
ChangeLog
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@ -1,5 +1,8 @@
2016-10-05 Siddhesh Poyarekar <siddhesh@sourceware.org>
* sysdeps/ieee754/dbl-64/s_sin.c (do_sincos_1): Check N
instead of K1.
* sysdeps/ieee754/dbl-64/s_sin.c (do_sincos_1): Rename K to
SHIFT_QUADRANT and make it bool.
(do_sincos_2): Likewise.

2
sysdeps/ieee754/dbl-64/s_sin.c
View File

@ -353,7 +353,7 @@ do_sincos_1 (double a, double da, double x, int4 n, bool shift_quadrant)
case 3:
res = do_cos (a, da, &cor);
cor = 1.025 * cor + __copysign (eps, cor);
retval = ((res == res + cor) ? ((k1 & 2) ? -res : res)
retval = ((res == res + cor) ? ((n & 2) ? -res : res)
: sloww2 (a, da, x, n));
break;
}