Annotation of src/lib/libm/src/s_cos.c, Revision 1.7
1.1 jtc 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: */
1.3 jtc 12:
1.6 jtc 13: #if defined(LIBM_SCCS) && !defined(lint)
1.7 ! jtc 14: static char rcsid[] = "$NetBSD: s_cos.c,v 1.6 1994/09/22 16:40:41 jtc Exp $";
1.3 jtc 15: #endif
1.1 jtc 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:
1.4 jtc 48: #include "math.h"
49: #include "math_private.h"
1.1 jtc 50:
51: #ifdef __STDC__
52: double cos(double x)
53: #else
54: double cos(x)
55: double x;
56: #endif
57: {
58: double y[2],z=0.0;
1.5 jtc 59: int32_t n, ix;
1.1 jtc 60:
61: /* High word of x. */
1.4 jtc 62: GET_HIGH_WORD(ix,x);
1.1 jtc 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: }
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