StdLib/LibC/Math/s_cos.c

   1 /* @(#)s_cos.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  */
  12 #include  <LibConfig.h>
  13 #include  <sys/EfiCdefs.h>
  14 #if defined(LIBM_SCCS) && !defined(lint)
  15 __RCSID("$NetBSD: s_cos.c,v 1.10 2002/05/26 22:01:54 wiz Exp $");
  16 #endif
  17
  18 /* cos(x)
  19  * Return cosine function of x.
  20  *
  21  * kernel function:
  22  *  __kernel_sin    ... sine function on [-pi/4,pi/4]
  23  *  __kernel_cos    ... cosine function on [-pi/4,pi/4]
  24  *  __ieee754_rem_pio2  ... argument reduction routine
  25  *
  26  * Method.
  27  *      Let S,C and T denote the sin, cos and tan respectively on
  28  *  [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
  29  *  in [-pi/4 , +pi/4], and let n = k mod 4.
  30  *  We have
  31  *
  32  *          n        sin(x)      cos(x)        tan(x)
  33  *     ----------------------------------------------------------
  34  *      0        S     C     T
  35  *      1        C    -S    -1/T
  36  *      2       -S    -C     T
  37  *      3       -C     S    -1/T
  38  *     ----------------------------------------------------------
  39  *
  40  * Special cases:
  41  *      Let trig be any of sin, cos, or tan.
  42  *      trig(+-INF)  is NaN, with signals;
  43  *      trig(NaN)    is that NaN;
  44  *
  45  * Accuracy:
  46  *  TRIG(x) returns trig(x) nearly rounded
  47  */
  48
  49 #include "math.h"
  50 #include "math_private.h"
  51
  52 double
  53 cos(double x)
  54 {
  55   double y[2],z=0.0;
  56   int32_t n, ix;
  57
  58     /* High word of x. */
  59   GET_HIGH_WORD(ix,x);
  60
  61     /* |x| ~< pi/4 */
  62   ix &= 0x7fffffff;
  63   if(ix <= 0x3fe921fb) return __kernel_cos(x,z);
  64
  65     /* cos(Inf or NaN) is NaN */
  66   else if (ix>=0x7ff00000) return x-x;
  67
  68     /* argument reduction needed */
  69   else {
  70       n = __ieee754_rem_pio2(x,y);
  71       switch(n&3) {
  72     case 0: return  __kernel_cos(y[0],y[1]);
  73     case 1: return -__kernel_sin(y[0],y[1],1);
  74     case 2: return -__kernel_cos(y[0],y[1]);
  75     default:
  76             return  __kernel_sin(y[0],y[1],1);
  77       }
  78   }
  79 }