s_sin.c revision 1.4 
1/* @(#)s_sin.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)
14static char rcsid[] = "$NetBSD: s_sin.c,v 1.7 1995/05/10 20:48:15 jtc Exp $";
15#endif
16
17/* sin(x)
18 * Return sine function of x.
19 *
20 * kernel function:
21 *	__kernel_sin		... sine function on [-pi/4,pi/4]
22 *	__kernel_cos		... cose 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 <sys/cdefs.h>
49#include <float.h>
50#include <math.h>
51
52#include "math_private.h"
53
54double
55sin(double x)
56{
57	double y[2],z=0.0;
58	int32_t n, ix;
59
60    /* High word of x. */
61	GET_HIGH_WORD(ix,x);
62
63    /* |x| ~< pi/4 */
64	ix &= 0x7fffffff;
65	if(ix <= 0x3fe921fb) return __kernel_sin(x,z,0);
66
67    /* sin(Inf or NaN) is NaN */
68	else if (ix>=0x7ff00000) return x-x;
69
70    /* argument reduction needed */
71	else {
72	    n = __ieee754_rem_pio2(x,y);
73	    switch(n&3) {
74		case 0: return  __kernel_sin(y[0],y[1],1);
75		case 1: return  __kernel_cos(y[0],y[1]);
76		case 2: return -__kernel_sin(y[0],y[1],1);
77		default:
78			return -__kernel_cos(y[0],y[1]);
79	    }
80	}
81}
82
83#if LDBL_MANT_DIG == 53
84#ifdef __weak_alias
85__weak_alias(sinl, sin);
86#endif /* __weak_alias */
87#endif /* LDBL_MANT_DIG == 53 */
88