sysdeps/ieee754/ldbl-128ibm/s_cosl.c

   1 /* s_cosl.c -- long double version of s_cos.c.
   2  * Conversion to long double by Jakub Jelinek, jj@ultra.linux.cz.
   3  */
   4
   5 /*
   6  * ====================================================
   7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   8  *
   9  * Developed at SunPro, a Sun Microsystems, Inc. business.
  10  * Permission to use, copy, modify, and distribute this
  11  * software is freely granted, provided that this notice
  12  * is preserved.
  13  * ====================================================
  14  */
  15
  16 /* cosl(x)
  17  * Return cosine function of x.
  18  *
  19  * kernel function:
  20  *      __kernel_sinl           ... sine function on [-pi/4,pi/4]
  21  *      __kernel_cosl           ... cosine function on [-pi/4,pi/4]
  22  *      __ieee754_rem_pio2l     ... argument reduction routine
  23  *
  24  * Method.
  25  *      Let S,C and T denote the sin, cos and tan respectively on
  26  *      [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
  27  *      in [-pi/4 , +pi/4], and let n = k mod 4.
  28  *      We have
  29  *
  30  *          n        sin(x)      cos(x)        tan(x)
  31  *     ----------------------------------------------------------
  32  *          0          S           C             T
  33  *          1          C          -S            -1/T
  34  *          2         -S          -C             T
  35  *          3         -C           S            -1/T
  36  *     ----------------------------------------------------------
  37  *
  38  * Special cases:
  39  *      Let trig be any of sin, cos, or tan.
  40  *      trig(+-INF)  is NaN, with signals;
  41  *      trig(NaN)    is that NaN;
  42  *
  43  * Accuracy:
  44  *      TRIG(x) returns trig(x) nearly rounded
  45  */
  46
  47 #include <errno.h>
  48 #include <math.h>
  49 #include <math_private.h>
  50 #include <math_ldbl_opt.h>
  51
  52 long double __cosl(long double x)
  53 {
  54         long double y[2],z=0.0L;
  55         int64_t n, ix;
  56         double xhi;
  57
  58     /* High word of x. */
  59         xhi = ldbl_high (x);
  60         EXTRACT_WORDS64 (ix, xhi);
  61
  62     /* |x| ~< pi/4 */
  63         ix &= 0x7fffffffffffffffLL;
  64         if(ix <= 0x3fe921fb54442d18LL)
  65           return __kernel_cosl(x,z);
  66
  67     /* cos(Inf or NaN) is NaN */
  68         else if (ix>=0x7ff0000000000000LL) {
  69             if (ix == 0x7ff0000000000000LL)
  70                 __set_errno (EDOM);
  71             return x-x;
  72         }
  73     /* argument reduction needed */
  74         else {
  75             n = __ieee754_rem_pio2l(x,y);
  76             switch(n&3) {
  77                 case 0:
  78                     return  __kernel_cosl(y[0],y[1]);
  79                 case 1:
  80                     return -__kernel_sinl(y[0],y[1],1);
  81                 case 2:
  82                     return -__kernel_cosl(y[0],y[1]);
  83                 default:
  84                     return  __kernel_sinl(y[0],y[1],1);
  85             }
  86         }
  87 }
  88 long_double_symbol (libm, __cosl, cosl);