1
2 /*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunSoft, 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 /* __kernel_sin( x, y, iy)
14 * kernel sin function on ~[-pi/4, pi/4] (except on -0), pi/4 ~ 0.7854
15 * Input x is assumed to be bounded by ~pi/4 in magnitude.
16 * Input y is the tail of x.
17 * Input iy indicates whether y is 0. (if iy=0, y assume to be 0).
18 *
19 * Algorithm
20 * 1. Since sin(-x) = -sin(x), we need only to consider positive x.
21 * 2. Callers must return sin(-0) = -0 without calling here since our
22 * odd polynomial is not evaluated in a way that preserves -0.
23 * Callers may do the optimization sin(x) ~ x for tiny x.
24 * 3. sin(x) is approximated by a polynomial of degree 13 on
25 * [0,pi/4]
26 * 3 13
27 * sin(x) ~ x + S1*x + ... + S6*x
28 * where
29 *
30 * |sin(x) 2 4 6 8 10 12 | -58
31 * |----- - (1+S1*x +S2*x +S3*x +S4*x +S5*x +S6*x )| <= 2
32 * | x |
33 *
34 * 4. sin(x+y) = sin(x) + sin'(x')*y
35 * ~ sin(x) + (1-x*x/2)*y
36 * For better accuracy, let
37 * 3 2 2 2 2
38 * r = x *(S2+x *(S3+x *(S4+x *(S5+x *S6))))
39 * then 3 2
40 * sin(x) = x + (S1*x + (x *(r-y/2)+y))
41 */
42
43 #include "math.h"
44 #include "math_private.h"
45
46 static const double
47 half = 5.00000000000000000000e-01, /* 0x3FE00000, 0x00000000 */
48 S1 = -1.66666666666666324348e-01, /* 0xBFC55555, 0x55555549 */
49 S2 = 8.33333333332248946124e-03, /* 0x3F811111, 0x1110F8A6 */
50 S3 = -1.98412698298579493134e-04, /* 0xBF2A01A0, 0x19C161D5 */
51 S4 = 2.75573137070700676789e-06, /* 0x3EC71DE3, 0x57B1FE7D */
52 S5 = -2.50507602534068634195e-08, /* 0xBE5AE5E6, 0x8A2B9CEB */
53 S6 = 1.58969099521155010221e-10; /* 0x3DE5D93A, 0x5ACFD57C */
54
55 double
__kernel_sin(double x,double y,int iy)56 __kernel_sin(double x, double y, int iy)
57 {
58 double z,r,v,w;
59
60 z = x*x;
61 w = z*z;
62 r = S2+z*(S3+z*S4) + z*w*(S5+z*S6);
63 v = z*x;
64 if(iy==0) return x+v*(S1+z*r);
65 else return x-((z*(half*y-v*r)-y)-v*S1);
66 }
67