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