/* @(#)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 <LibConfig.h> | |
#include <sys/EfiCdefs.h> | |
#if defined(LIBM_SCCS) && !defined(lint) | |
__RCSID("$NetBSD: s_cos.c,v 1.10 2002/05/26 22:01:54 wiz 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" | |
double | |
cos(double x) | |
{ | |
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); | |
} | |
} | |
} |