src/libm/s_cos.c
author Philipp Wiesemann <philipp.wiesemann@arcor.de>
Sun, 28 Dec 2014 22:00:24 +0100
changeset 9301 7377a9a3aed6
parent 6044 35448a5ea044
child 11683 48bcba563d9c
permissions -rw-r--r--
Renamed README-emscripten.txt to README-emscripten.md.
     1 /* @(#)s_cos.c 5.1 93/09/24 */
     2 /*
     3  * ====================================================
     4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
     5  *
     6  * Developed at SunPro, a Sun Microsystems, Inc. business.
     7  * Permission to use, copy, modify, and distribute this
     8  * software is freely granted, provided that this notice
     9  * is preserved.
    10  * ====================================================
    11  */
    12 
    13 #if defined(LIBM_SCCS) && !defined(lint)
    14 static const char rcsid[] =
    15     "$NetBSD: s_cos.c,v 1.7 1995/05/10 20:47:02 jtc Exp $";
    16 #endif
    17 
    18 /* cos(x)
    19  * Return cosine function of x.
    20  *
    21  * kernel function:
    22  *	__kernel_sin		... sine function on [-pi/4,pi/4]
    23  *	__kernel_cos		... cosine function on [-pi/4,pi/4]
    24  *	__ieee754_rem_pio2	... argument reduction routine
    25  *
    26  * Method.
    27  *      Let S,C and T denote the sin, cos and tan respectively on
    28  *	[-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
    29  *	in [-pi/4 , +pi/4], and let n = k mod 4.
    30  *	We have
    31  *
    32  *          n        sin(x)      cos(x)        tan(x)
    33  *     ----------------------------------------------------------
    34  *	    0	       S	   C		 T
    35  *	    1	       C	  -S		-1/T
    36  *	    2	      -S	  -C		 T
    37  *	    3	      -C	   S		-1/T
    38  *     ----------------------------------------------------------
    39  *
    40  * Special cases:
    41  *      Let trig be any of sin, cos, or tan.
    42  *      trig(+-INF)  is NaN, with signals;
    43  *      trig(NaN)    is that NaN;
    44  *
    45  * Accuracy:
    46  *	TRIG(x) returns trig(x) nearly rounded
    47  */
    48 
    49 #include "math_libm.h"
    50 #include "math_private.h"
    51 
    52 libm_hidden_proto(cos)
    53 #ifdef __STDC__
    54      double cos(double x)
    55 #else
    56      double cos(x)
    57      double x;
    58 #endif
    59 {
    60     double y[2], z = 0.0;
    61     int32_t n, ix;
    62 
    63     /* High word of x. */
    64     GET_HIGH_WORD(ix, x);
    65 
    66     /* |x| ~< pi/4 */
    67     ix &= 0x7fffffff;
    68     if (ix <= 0x3fe921fb)
    69         return __kernel_cos(x, z);
    70 
    71     /* cos(Inf or NaN) is NaN */
    72     else if (ix >= 0x7ff00000)
    73         return x - x;
    74 
    75     /* argument reduction needed */
    76     else {
    77         n = __ieee754_rem_pio2(x, y);
    78         switch (n & 3) {
    79         case 0:
    80             return __kernel_cos(y[0], y[1]);
    81         case 1:
    82             return -__kernel_sin(y[0], y[1], 1);
    83         case 2:
    84             return -__kernel_cos(y[0], y[1]);
    85         default:
    86             return __kernel_sin(y[0], y[1], 1);
    87         }
    88     }
    89 }
    90 
    91 libm_hidden_def(cos)