1
2 /* @(#)s_cos.c 5.1 93/09/24 */
3 /*
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 *
7 * Developed at SunPro, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
10 * is preserved.
11 * ====================================================
12 */
13
14 /* cos(x)
15 * Return cosine function of x.
16 *
17 * kernel function:
18 * __kernel_sin ... sine function on [-pi/4,pi/4]
19 * __kernel_cos ... cosine function on [-pi/4,pi/4]
20 * __rem_pio2 ... argument reduction routine
21 *
22 * Method.
23 * Let S,C and T denote the sin, cos and tan respectively on
24 * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
25 * in [-pi/4 , +pi/4], and let n = k mod 4.
26 * We have
27 *
28 * n sin(x) cos(x) tan(x)
29 * ----------------------------------------------------------
30 * 0 S C T
31 * 1 C -S -1/T
32 * 2 -S -C T
33 * 3 -C S -1/T
34 * ----------------------------------------------------------
35 *
36 * Special cases:
37 * Let trig be any of sin, cos, or tan.
38 * trig(+-INF) is NaN, with signals;
39 * trig(NaN) is that NaN;
40 *
41 * Accuracy:
42 * TRIG(x) returns trig(x) nearly rounded
43 */
44
45 #include "fdlibm.h"
46
47 #ifdef _NEED_FLOAT64
48
49 __float64
cos64(__float64 x)50 cos64(__float64 x)
51 {
52 __float64 y[2], z = 0.0;
53 __int32_t n, ix;
54
55 /* High word of x. */
56 GET_HIGH_WORD(ix, x);
57
58 /* |x| ~< pi/4 */
59 ix &= 0x7fffffff;
60 if (ix <= 0x3fe921fb)
61 return __kernel_cos(x, z);
62
63 /* cos(Inf or NaN) is NaN */
64 else if (ix >= 0x7ff00000)
65 return __math_invalid(x);
66
67 /* argument reduction needed */
68 else {
69 n = __rem_pio2(x, y);
70 switch (n & 3) {
71 case 0:
72 return __kernel_cos(y[0], y[1]);
73 case 1:
74 return -__kernel_sin(y[0], y[1], 1);
75 case 2:
76 return -__kernel_cos(y[0], y[1]);
77 default:
78 return __kernel_sin(y[0], y[1], 1);
79 }
80 }
81 }
82
83 #if defined(_HAVE_ALIAS_ATTRIBUTE)
84 #ifndef __clang__
85 #pragma GCC diagnostic ignored "-Wmissing-attributes"
86 #endif
87 __strong_reference(_NAME_64(cos), _NAME_64(_cos));
88 #endif
89
90 _MATH_ALIAS_d_d(cos)
91
92 #endif /* _NEED_FLOAT64 */
93
