| 1 |
gwlarson |
3.1 |
#ifndef lint
|
| 2 |
schorsch |
3.4 |
static const char RCSid[] = "$Id: tcos.c,v 3.3 2003/02/25 02:47:22 greg Exp $";
|
| 3 |
gwlarson |
3.1 |
#endif
|
| 4 |
|
|
/*
|
| 5 |
|
|
* Table-based cosine approximation.
|
| 6 |
|
|
*
|
| 7 |
|
|
* Use doubles in table even though we're not nearly that accurate just
|
| 8 |
|
|
* to avoid conversion and guarantee that tsin(x)^2 + tcos(x)^2 == 1.
|
| 9 |
|
|
*
|
| 10 |
|
|
* No interpolation in this version.
|
| 11 |
greg |
3.2 |
*
|
| 12 |
|
|
* External symbols declared in standard.h
|
| 13 |
|
|
*/
|
| 14 |
|
|
|
| 15 |
greg |
3.3 |
#include "copyright.h"
|
| 16 |
gwlarson |
3.1 |
|
| 17 |
|
|
#include <math.h>
|
| 18 |
schorsch |
3.4 |
|
| 19 |
|
|
#include "rtmath.h"
|
| 20 |
gwlarson |
3.1 |
|
| 21 |
|
|
#ifndef NCOSENTRY
|
| 22 |
|
|
#define NCOSENTRY 256
|
| 23 |
|
|
#endif
|
| 24 |
|
|
|
| 25 |
|
|
#ifdef M_PI
|
| 26 |
|
|
#define PI ((double)M_PI)
|
| 27 |
|
|
#else
|
| 28 |
|
|
#define PI 3.14159265358979323846
|
| 29 |
|
|
#endif
|
| 30 |
|
|
|
| 31 |
|
|
|
| 32 |
|
|
double
|
| 33 |
|
|
tcos(x) /* approximate cosine */
|
| 34 |
|
|
register double x;
|
| 35 |
|
|
{
|
| 36 |
|
|
static double costab[NCOSENTRY+1];
|
| 37 |
|
|
register int i;
|
| 38 |
|
|
|
| 39 |
|
|
if (costab[0] < 0.5) /* initialize table */
|
| 40 |
|
|
for (i = 0; i <= NCOSENTRY; i++)
|
| 41 |
|
|
costab[i] = cos((PI/2./NCOSENTRY)*i);
|
| 42 |
|
|
/* normalize angle */
|
| 43 |
|
|
if (x < 0.)
|
| 44 |
|
|
x = -x;
|
| 45 |
|
|
i = (NCOSENTRY*2./PI) * x + 0.5;
|
| 46 |
|
|
if (i >= 4*NCOSENTRY)
|
| 47 |
|
|
i %= 4*NCOSENTRY;
|
| 48 |
|
|
switch (i / NCOSENTRY) {
|
| 49 |
|
|
case 0:
|
| 50 |
|
|
return(costab[i]);
|
| 51 |
|
|
case 1:
|
| 52 |
|
|
return(-costab[(2*NCOSENTRY)-i]);
|
| 53 |
|
|
case 2:
|
| 54 |
|
|
return(-costab[i-(2*NCOSENTRY)]);
|
| 55 |
|
|
case 3:
|
| 56 |
|
|
return(costab[(4*NCOSENTRY)-i]);
|
| 57 |
|
|
}
|
| 58 |
|
|
return(0.); /* should never be reached */
|
| 59 |
|
|
}
|
