libjava/java/lang/s_cos.c

   1
   2 /* @(#)s_cos.c 5.1 93/09/24 */
   3 /*
   4  * ====================================================
   5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   6  *
   7  * Developed at SunPro, a Sun Microsystems, Inc. business.
   8  * Permission to use, copy, modify, and distribute this
   9  * software is freely granted, provided that this notice
  10  * is preserved.
  11  * ====================================================
  12  */
  13
  14 /* cos(x)
  15  * Return cosine function of x.
  16  *
  17  * kernel function:
  18  *      __kernel_sin            ... sine function on [-pi/4,pi/4]
  19  *      __kernel_cos            ... cosine function on [-pi/4,pi/4]
  20  *      __ieee754_rem_pio2      ... argument reduction routine
  21  *
  22  * Method.
  23  *      Let S,C and T denote the sin, cos and tan respectively on
  24  *      [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
  25  *      in [-pi/4 , +pi/4], and let n = k mod 4.
  26  *      We have
  27  *
  28  *          n        sin(x)      cos(x)        tan(x)
  29  *     ----------------------------------------------------------
  30  *          0          S           C             T
  31  *          1          C          -S            -1/T
  32  *          2         -S          -C             T
  33  *          3         -C           S            -1/T
  34  *     ----------------------------------------------------------
  35  *
  36  * Special cases:
  37  *      Let trig be any of sin, cos, or tan.
  38  *      trig(+-INF)  is NaN, with signals;
  39  *      trig(NaN)    is that NaN;
  40  *
  41  * Accuracy:
  42  *      TRIG(x) returns trig(x) nearly rounded
  43  */
  44
  45 #include "fdlibm.h"
  46
  47 #ifndef _DOUBLE_IS_32BITS
  48
  49 #ifdef __STDC__
  50         double cos(double x)
  51 #else
  52         double cos(x)
  53         double x;
  54 #endif
  55 {
  56         double y[2],z=0.0;
  57         int32_t n,ix;
  58
  59     /* High word of x. */
  60         GET_HIGH_WORD(ix,x);
  61
  62     /* |x| ~< pi/4 */
  63         ix &= 0x7fffffff;
  64         if(ix <= 0x3fe921fb) return __kernel_cos(x,z);
  65
  66     /* cos(Inf or NaN) is NaN */
  67         else if (ix>=0x7ff00000) return x-x;
  68
  69     /* argument reduction needed */
  70         else {
  71             n = __ieee754_rem_pio2(x,y);
  72             switch(n&3) {
  73                 case 0: return  __kernel_cos(y[0],y[1]);
  74                 case 1: return -__kernel_sin(y[0],y[1],1);
  75                 case 2: return -__kernel_cos(y[0],y[1]);
  76                 default:
  77                         return  __kernel_sin(y[0],y[1],1);
  78             }
  79         }
  80 }
  81
  82 #endif /* _DOUBLE_IS_32BITS */