src/MSL_C.PPCEABI.bare.H/s_cos.c


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75


/* @(#)s_cos.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */
/* cos(x)
 * Return cosine function of x.
 *
 * kernel function:
 *	__kernel_sin		... sine function on [-pi/4,pi/4]
 *	__kernel_cos		... cosine function on [-pi/4,pi/4]
 *	__ieee754_rem_pio2	... argument reduction routine
 *
 * Method.
 *      Let S,C and T denote the sin, cos and tan respectively on
 *	[-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
 *	in [-pi/4 , +pi/4], and let n = k mod 4.
 *	We have
 *
 *          n        sin(x)      cos(x)        tan(x)
 *     ----------------------------------------------------------
 *	    0	       S	   C		 T
 *	    1	       C	  -S		-1/T
 *	    2	      -S	  -C		 T
 *	    3	      -C	   S		-1/T
 *     ----------------------------------------------------------
 *
 * Special cases:
 *      Let trig be any of sin, cos, or tan.
 *      trig(+-INF)  is NaN, with signals;
 *      trig(NaN)    is that NaN;
 *
 * Accuracy:
 *	TRIG(x) returns trig(x) nearly rounded
 */
#include "fdlibm.h"
#ifdef __STDC__
double cos(double x)
#else
double cos(x)
double x;
#endif
{
  double y[2], z = 0.0;
  int n, ix;
  /* High word of x. */
  ix = __HI(x);
  /* |x| ~< pi/4 */
  ix &= 0x7fffffff;
  if (ix <= 0x3fe921fb)
    return __kernel_cos(x, z);
  /* cos(Inf or NaN) is NaN */
  else if (ix >= 0x7ff00000)
    return x - x;
  /* argument reduction needed */
  else {
    n = __ieee754_rem_pio2(x, y);
    switch (n & 3) {
    case 0:
      return __kernel_cos(y[0], y[1]);
    case 1:
      return -__kernel_sin(y[0], y[1], 1);
    case 2:
      return -__kernel_cos(y[0], y[1]);
    default:
      return __kernel_sin(y[0], y[1], 1);
    }
  }
}