StdLib/LibC/Math/s_cos.c

/* @(#)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);
      }
  }
}