text: /* @(#)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.
   * ====================================================
   */
  
  #if defined(LIBM_SCCS) && !defined(lint)
  static const 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_libm.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)
  