Subversion Repositories shark

Rev

Rev 1618 | Details | Compare with Previous | Last modification | View Log | RSS feed

Rev Author Line No. Line
2 pj 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
#ifndef lint
14
static char rcsid[] = "$\Id: s_cos.c,v 1.2.6.1 1997/02/23 11:03:17 joerg Exp $";
15
#endif
16
 
17
/* cos(x)
18
 * Return cosine function of x.
19
 *
20
 * kernel function:
21
 *      __kernel_sin            ... sine function on [-pi/4,pi/4]
22
 *      __kernel_cos            ... cosine function on [-pi/4,pi/4]
23
 *      __ieee754_rem_pio2      ... argument reduction routine
24
 *
25
 * Method.
26
 *      Let S,C and T denote the sin, cos and tan respectively on
27
 *      [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
28
 *      in [-pi/4 , +pi/4], and let n = k mod 4.
29
 *      We have
30
 *
31
 *          n        sin(x)      cos(x)        tan(x)
32
 *     ----------------------------------------------------------
33
 *          0          S           C             T
34
 *          1          C          -S            -1/T
35
 *          2         -S          -C             T
36
 *          3         -C           S            -1/T
37
 *     ----------------------------------------------------------
38
 *
39
 * Special cases:
40
 *      Let trig be any of sin, cos, or tan.
41
 *      trig(+-INF)  is NaN, with signals;
42
 *      trig(NaN)    is that NaN;
43
 *
44
 * Accuracy:
45
 *      TRIG(x) returns trig(x) nearly rounded
46
 */
47
 
48
#include "math.h"
49
#include "math_private.h"
50
 
51
#ifdef __STDC__
52
        double __generic_cos(double x)
53
#else
54
        double __generic_cos(x)
55
        double x;
56
#endif
57
{
58
        double y[2],z=0.0;
59
        int32_t n, ix;
60
 
61
    /* High word of x. */
62
        GET_HIGH_WORD(ix,x);
63
 
64
    /* |x| ~< pi/4 */
65
        ix &= 0x7fffffff;
66
        if(ix <= 0x3fe921fb) return __kernel_cos(x,z);
67
 
68
    /* cos(Inf or NaN) is NaN */
69
        else if (ix>=0x7ff00000) return x-x;
70
 
71
    /* argument reduction needed */
72
        else {
73
            n = __ieee754_rem_pio2(x,y);
74
            switch(n&3) {
75
                case 0: return  __kernel_cos(y[0],y[1]);
76
                case 1: return -__kernel_sin(y[0],y[1],1);
77
                case 2: return -__kernel_cos(y[0],y[1]);
78
                default:
79
                        return  __kernel_sin(y[0],y[1],1);
80
            }
81
        }
82
}