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Length: 7990 (0x1f36)
Types: TextFile
Names: »trigtab.c«
└─⟦b20c6495f⟧ Bits:30007238 EUUGD18: Wien-båndet, efterår 1987
└─⟦this⟧ »EUUGD18/X/Xtrek/trigtab.c«
static char sccsid[] = "@(#)trigtab.c 1.1";
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/*
** table for computing inverse tangent values
*/
long iatan[] = {
0,
201,
402,
604,
806,
1010,
1215,
1421,
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1839,
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5769,
6075,
6393,
6723,
7066,
7424,
7799,
8192,
8604,
9038,
9496,
9981,
10497,
11045,
11631,
12260,
12936,
13667,
14460,
15326,
16274,
17320,
18480,
19777,
21236,
22895,
24797,
27005,
29602,
32704,
36480,
41183,
47211,
55225,
66418,
83174,
111056,
166751,
333705
};
#include <X11/Xlib.h>
#include "defs.h"
unsigned char iatan2(y, x)
int x, y;
{
int bottom, top, i;
long z, scaled_y;
scaled_y = y << TRIGSCALE;
if (x == 0) i = (y >= 0 ? 64 : 192);
else {
z = abs(scaled_y/x);
#ifdef DEBUG
printf("Looking for closest table value to %ld\n", z);
#endif DEBUG
bottom = 0;
top = sizeof(iatan)/sizeof(long) - 1;
/*-------------------------------------------------------------------------
* Loop Invariant: top - bottom > 1 && iatan[bottom] < z <= iatan[top]
*
* At end of loop this guarantees:
* top-bottom <= 1 && top-prev_bottom > 1 ==> top-bottom = 1
* Also iatan[bottom] < z <= iatan[top]. So we will return the closer of
* these two values.
*-------------------------------------------------------------------------
*/
while (top-bottom > 1) {
i = bottom + ((top-bottom)>>1);
if (iatan[i] < z) bottom = i;
else top = i;
}
/* Choose the closer of the two values */
i = (abs(iatan[top] - z) < abs(iatan[bottom] - z)) ? top : bottom;
} /* else */
#ifdef DEBUG
printf("original i: %d; ", i);
#endif DEBUG
if (y == 0) i = (x >= 0) ? 0 : 128;
else if (x < 0 && y > 0) i = 128-i;
else if (x < 0 && y < 0) i += 128;
else if (x > 0 && y < 0) i = 256-i;
#ifdef DEBUG
printf("iatan2(%d, %d) = %d\n", y, x, i);
#endif DEBUG
return(i);
}
/*
* The isin and icos routines in trigtab.c are made to work in the obscure
* coordinate system used by xtrek (angles measured from the positive y axis).
* This routine snags out 1/4 of the isin table and uses it to produce
* values of the sin function from the normal coordinate system. This
* has the advantage of making things like the law of sines work.
*/
int
normal_isin(in_angle)
unsigned char in_angle;
{
int minus = 1;
unsigned char angle = in_angle;
/* sin(a) = -sin(a-pi) */
if (angle > 128) {
angle = angle - 128;
minus *= -1;
}
/* sin(a) = sin(pi-a) */
if (angle > 64) {
angle = 128 - angle;
}
angle = angle + 64; /* stupid isin table is broken */
return(isin[angle]);
}