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rtl_fm: crude integer atan2, around 40% faster

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Signed-off-by: Steve Markgraf <steve@steve-m.de>
This commit is contained in:
Kyle Keen 2012-05-31 02:53:31 -04:00 committed by Steve Markgraf
parent 6e80117205
commit 62cc815863
1 changed files with 25 additions and 2 deletions
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27
src/rtl_fm.c
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@ -182,13 +182,36 @@ void multiply(int ar, int aj, int br, int bj, int *cr, int *cj)
*cj = aj*br + ar*bj; *cj = aj*br + ar*bj;
} }
int fast_atan2(int y, int x)
/* pre scaled for int16 */
{
int yabs, angle, pi4=(1<<12); // note pi = 1<<14
if (x==0 && y==0) {
return 0;
}
yabs = y;
if (yabs < 0) {
yabs = -yabs;
}
if (x >= 0) {
angle = pi4 - pi4 * (x-yabs) / (x+yabs);
} else {
angle = 3*pi4 - pi4 * (x+yabs) / (yabs-x);
}
if (y < 0) {
return -angle;
}
return angle;
}
int polar_discriminant(int ar, int aj, int br, int bj) int polar_discriminant(int ar, int aj, int br, int bj)
{ {
int cr, cj; int cr, cj;
double angle; double angle;
multiply(ar, aj, br, -bj, &cr, &cj); multiply(ar, aj, br, -bj, &cr, &cj);
angle = atan2((double)cj, (double)cr); //angle = atan2((double)cj, (double)cr);
return (int)(angle / 3.14159 * (1<<14)); //return (int)(angle / 3.14159 * (1<<14));
return fast_atan2(cj, cr);
} }
void fm_demod(struct fm_state *fm) void fm_demod(struct fm_state *fm)