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  #if defined(LIBM_SCCS) && !defined(lint)
      16  static char rcsid[] = "$NetBSD: $";
      17  #endif
      18  
      19  /* cosl(x)
      20   * Return cosine function of x.
      21   *
      22   * kernel function:
      23   *	__kernel_sinl		... sine function on [-pi/4,pi/4]
      24   *	__kernel_cosl		... cosine function on [-pi/4,pi/4]
      25   *	__ieee754_rem_pio2l	... argument reduction routine
      26   *
      27   * Method.
      28   *      Let S,C and T denote the sin, cos and tan respectively on
      29   *	[-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
      30   *	in [-pi/4 , +pi/4], and let n = k mod 4.
      31   *	We have
      32   *
      33   *          n        sin(x)      cos(x)        tan(x)
      34   *     ----------------------------------------------------------
      35   *	    0	       S	   C		 T
      36   *	    1	       C	  -S		-1/T
      37   *	    2	      -S	  -C		 T
      38   *	    3	      -C	   S		-1/T
      39   *     ----------------------------------------------------------
      40   *
      41   * Special cases:
      42   *      Let trig be any of sin, cos, or tan.
      43   *      trig(+-INF)  is NaN, with signals;
      44   *      trig(NaN)    is that NaN;
      45   *
      46   * Accuracy:
      47   *	TRIG(x) returns trig(x) nearly rounded
      48   */
      49  
      50  #include <errno.h>
      51  #include <math.h>
      52  #include <math_private.h>
      53  #include <libm-alias-ldouble.h>
      54  
      55  long double __cosl(long double x)
      56  {
      57  	long double y[2],z=0.0;
      58  	int32_t n, se, i0, i1;
      59  
      60      /* High word of x. */
      61  	GET_LDOUBLE_WORDS(se,i0,i1,x);
      62  
      63      /* |x| ~< pi/4 */
      64  	se &= 0x7fff;
      65  	if(se < 0x3ffe || (se == 0x3ffe && i0 <= 0xc90fdaa2))
      66  	  return __kernel_cosl(x,z);
      67  
      68      /* cos(Inf or NaN) is NaN */
      69  	else if (se==0x7fff) {
      70  	  if (i1 == 0 && i0 == 0x80000000)
      71  	    __set_errno (EDOM);
      72  	  return x-x;
      73  	}
      74  
      75      /* argument reduction needed */
      76  	else {
      77  	    n = __ieee754_rem_pio2l(x,y);
      78  	    switch(n&3) {
      79  		case 0: return  __kernel_cosl(y[0],y[1]);
      80  		case 1: return -__kernel_sinl(y[0],y[1],1);
      81  		case 2: return -__kernel_cosl(y[0],y[1]);
      82  		default:
      83  		        return  __kernel_sinl(y[0],y[1],1);
      84  	    }
      85  	}
      86  }
      87  libm_alias_ldouble (__cos, cos)