src/libm/k_sin.c
 author Sam Lantinga Mon, 15 Sep 2008 06:33:23 +0000 changeset 2756 a98604b691c8 child 3162 dc1eb82ffdaa permissions -rw-r--r--
Expanded the libm support and put it into a separate directory.
```
/* @(#)k_sin.c 5.1 93/09/24 */
/*
* ====================================================
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/

#if defined(LIBM_SCCS) && !defined(lint)
static char rcsid[] = "\$NetBSD: k_sin.c,v 1.8 1995/05/10 20:46:31 jtc Exp \$";
#endif

/* __kernel_sin( x, y, iy)
* kernel sin function on [-pi/4, pi/4], pi/4 ~ 0.7854
* Input x is assumed to be bounded by ~pi/4 in magnitude.
* Input y is the tail of x.
* Input iy indicates whether y is 0. (if iy=0, y assume to be 0).
*
* Algorithm
*	1. Since sin(-x) = -sin(x), we need only to consider positive x.
*	2. if x < 2^-27 (hx<0x3e400000 0), return x with inexact if x!=0.
*	3. sin(x) is approximated by a polynomial of degree 13 on
*	   [0,pi/4]
*		  	         3            13
*	   	sin(x) ~ x + S1*x + ... + S6*x
*	   where
*
* 	|sin(x)         2     4     6     8     10     12  |     -58
* 	|----- - (1+S1*x +S2*x +S3*x +S4*x +S5*x  +S6*x   )| <= 2
* 	|  x 					           |
*
*	4. sin(x+y) = sin(x) + sin'(x')*y
*		    ~ sin(x) + (1-x*x/2)*y
*	   For better accuracy, let
*		     3      2      2      2      2
*		r = x *(S2+x *(S3+x *(S4+x *(S5+x *S6))))
*	   then                   3    2
*		sin(x) = x + (S1*x + (x *(r-y/2)+y))
*/

#include "math.h"
#include "math_private.h"

#ifdef __STDC__
static const double
#else
static double
#endif
half = 5.00000000000000000000e-01,    /* 0x3FE00000, 0x00000000 */
S1 = -1.66666666666666324348e-01,   /* 0xBFC55555, 0x55555549 */
S2 = 8.33333333332248946124e-03,    /* 0x3F811111, 0x1110F8A6 */
S3 = -1.98412698298579493134e-04,   /* 0xBF2A01A0, 0x19C161D5 */
S4 = 2.75573137070700676789e-06,    /* 0x3EC71DE3, 0x57B1FE7D */
S5 = -2.50507602534068634195e-08,   /* 0xBE5AE5E6, 0x8A2B9CEB */
S6 = 1.58969099521155010221e-10;    /* 0x3DE5D93A, 0x5ACFD57C */

#ifdef __STDC__
double attribute_hidden
__kernel_sin(double x, double y, int iy)
#else
double attribute_hidden
__kernel_sin(x, y, iy)
double x, y;
int iy;                    /* iy=0 if y is zero */
#endif
{
double z, r, v;
int32_t ix;
GET_HIGH_WORD(ix, x);
ix &= 0x7fffffff;           /* high word of x */
if (ix < 0x3e400000) {      /* |x| < 2**-27 */
if ((int) x == 0)
return x;
}                           /* generate inexact */
z = x * x;
v = z * x;
r = S2 + z * (S3 + z * (S4 + z * (S5 + z * S6)));
if (iy == 0)
return x + v * (S1 + z * r);
else
return x - ((z * (half * y - v * r) - y) - v * S1);
}
```