src/libm/s_cos.c
 author Holmes Futrell Thu, 01 Jan 2009 23:49:28 +0000 changeset 2950 04c9f1e4c496 parent 2756 a98604b691c8 child 3162 dc1eb82ffdaa permissions -rw-r--r--
Added target testdraw2 for running the test/testdraw2.c test.
```
/* @(#)s_cos.c 5.1 93/09/24 */
/*
* ====================================================
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/

#if defined(LIBM_SCCS) && !defined(lint)
static char rcsid[] = "\$NetBSD: s_cos.c,v 1.7 1995/05/10 20:47:02 jtc Exp \$";
#endif

/* cos(x)
* Return cosine function of x.
*
* kernel function:
*	__kernel_sin		... sine function on [-pi/4,pi/4]
*	__kernel_cos		... cosine function on [-pi/4,pi/4]
*	__ieee754_rem_pio2	... argument reduction routine
*
* Method.
*      Let S,C and T denote the sin, cos and tan respectively on
*	[-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
*	in [-pi/4 , +pi/4], and let n = k mod 4.
*	We have
*
*          n        sin(x)      cos(x)        tan(x)
*     ----------------------------------------------------------
*	    0	       S	   C		 T
*	    1	       C	  -S		-1/T
*	    2	      -S	  -C		 T
*	    3	      -C	   S		-1/T
*     ----------------------------------------------------------
*
* Special cases:
*      Let trig be any of sin, cos, or tan.
*      trig(+-INF)  is NaN, with signals;
*      trig(NaN)    is that NaN;
*
* Accuracy:
*	TRIG(x) returns trig(x) nearly rounded
*/

#include "math.h"
#include "math_private.h"

libm_hidden_proto(cos)
#ifdef __STDC__
double cos(double x)
#else
double cos(x)
double x;
#endif
{
double y[2], z = 0.0;
int32_t n, ix;

/* High word of x. */
GET_HIGH_WORD(ix, x);

/* |x| ~< pi/4 */
ix &= 0x7fffffff;
if (ix <= 0x3fe921fb)
return __kernel_cos(x, z);

/* cos(Inf or NaN) is NaN */
else if (ix >= 0x7ff00000)
return x - x;

/* argument reduction needed */
else {
n = __ieee754_rem_pio2(x, y);
switch (n & 3) {
case 0:
return __kernel_cos(y[0], y[1]);
case 1:
return -__kernel_sin(y[0], y[1], 1);
case 2:
return -__kernel_cos(y[0], y[1]);
default:
return __kernel_sin(y[0], y[1], 1);
}
}
}

libm_hidden_def(cos)
```