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File: [cvs.NetBSD.org] / src / lib / libm / src / s_cos.c (download)

Revision 1.9, Fri Jul 2 15:37:42 1999 UTC (24 years, 9 months ago) by simonb
Branch: MAIN
CVS Tags: wrstuden-devbsize-base, wrstuden-devbsize-19991221, wrstuden-devbsize, netbsd-1-6-base, netbsd-1-6-RELEASE, netbsd-1-6-RC3, netbsd-1-6-RC2, netbsd-1-6-RC1, netbsd-1-6-PATCH002-RELEASE, netbsd-1-6-PATCH002-RC4, netbsd-1-6-PATCH002-RC3, netbsd-1-6-PATCH002-RC2, netbsd-1-6-PATCH002-RC1, netbsd-1-6-PATCH002, netbsd-1-6-PATCH001-RELEASE, netbsd-1-6-PATCH001-RC3, netbsd-1-6-PATCH001-RC2, netbsd-1-6-PATCH001-RC1, netbsd-1-6-PATCH001, netbsd-1-6, netbsd-1-5-base, netbsd-1-5-RELEASE, netbsd-1-5-PATCH003, netbsd-1-5-PATCH002, netbsd-1-5-PATCH001, netbsd-1-5-BETA2, netbsd-1-5-BETA, netbsd-1-5-ALPHA2, netbsd-1-5, minoura-xpg4dl-base, minoura-xpg4dl, comdex-fall-1999-base, comdex-fall-1999
Changes since 1.8: +5 -5 lines

More trailing white space.

/* @(#)s_cos.c 5.1 93/09/24 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * 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.
 * ====================================================
 */

#include <sys/cdefs.h>
#if defined(LIBM_SCCS) && !defined(lint)
__RCSID("$NetBSD: s_cos.c,v 1.9 1999/07/02 15:37:42 simonb 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"

#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);
	    }
	}
}