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authorKyle Keen <keenerd@gmail.com>2013-01-29 21:38:27 -0500
committerSteve Markgraf <steve@steve-m.de>2013-01-30 20:24:24 +0100
commitc85cab2dae0ed59e244a2160fa632596c9707eb9 (patch)
treee7e30f88d7070959eb788604a7578bcb9df11be7 /src/rtl_fm.c
parentc6a731a0dcff882edb4777a816865f525966464d (diff)
rtl_fm: Miroslav SlugeĊˆ's atan lut
Signed-off-by: Steve Markgraf <steve@steve-m.de>
Diffstat (limited to 'src/rtl_fm.c')
-rw-r--r--src/rtl_fm.c82
1 files changed, 75 insertions, 7 deletions
diff --git a/src/rtl_fm.c b/src/rtl_fm.c
index 45f8e06..8009876 100644
--- a/src/rtl_fm.c
+++ b/src/rtl_fm.c
@@ -72,6 +72,10 @@ static int do_exit = 0;
static rtlsdr_dev_t *dev = NULL;
static int lcm_post[17] = {1,1,1,3,1,5,3,7,1,9,5,11,3,13,7,15,1};
+static int *atan_lut = NULL;
+static int atan_lut_size = 131072; /* 512 KB */
+static int atan_lut_coef = 8;
+
struct fm_state
{
int now_r;
@@ -128,7 +132,7 @@ void usage(void)
"\t[-E sets lower edge tuning (default: center)]\n"
"\t[-N enables NBFM mode (default: on)]\n"
"\t[-W enables WBFM mode (default: off)]\n"
- "\t (-N -s 170k -o 4 -A -r 32k -l 0 -D)\n"
+ "\t (-N -s 170k -o 4 -A fast -r 32k -l 0 -D)\n"
"\tfilename (a '-' dumps samples to stdout)\n"
"\t (omitting the filename also uses stdout)\n\n"
"Experimental options:\n"
@@ -142,7 +146,7 @@ void usage(void)
"\t[-R enables raw mode (default: off, 2x16 bit output)]\n"
"\t[-F enables high quality FIR (default: off/square)]\n"
"\t[-D enables de-emphasis (default: off)]\n"
- "\t[-A enables high speed arctan (default: off)]\n\n"
+ "\t[-A std/fast/lut choose atan math (default: std)]\n\n"
"Produces signed 16 bit ints, use Sox or aplay to hear them.\n"
"\trtl_fm ... - | play -t raw -r 24k -e signed-integer -b 16 -c 1 -V1 -\n"
"\t | aplay -r 24k -f S16_LE -t raw -c 1\n"
@@ -343,6 +347,57 @@ int polar_disc_fast(int ar, int aj, int br, int bj)
return fast_atan2(cj, cr);
}
+int atan_lut_init()
+{
+ int i = 0;
+
+ atan_lut = malloc(atan_lut_size * sizeof(int));
+
+ for (i = 0; i < atan_lut_size; i++) {
+ atan_lut[i] = (int) (atan((double) i / (1<<atan_lut_coef)) / 3.14159 * (1<<14));
+ }
+
+ return 0;
+}
+
+int polar_disc_lut(int ar, int aj, int br, int bj)
+{
+ int cr, cj, x, x_abs;
+
+ multiply(ar, aj, br, -bj, &cr, &cj);
+
+ /* special cases */
+ if (cr == 0 || cj == 0) {
+ if (cr == 0 && cj == 0)
+ {return 0;}
+ if (cr == 0 && cj > 0)
+ {return 1 << 13;}
+ if (cr == 0 && cj < 0)
+ {return -(1 << 13);}
+ if (cj == 0 && cr > 0)
+ {return 0;}
+ if (cj == 0 && cr < 0)
+ {return 1 << 14;}
+ }
+
+ /* real range -32768 - 32768 use 64x range -> absolute maximum: 2097152 */
+ x = (cj << atan_lut_coef) / cr;
+ x_abs = abs(x);
+
+ if (x_abs >= atan_lut_size) {
+ /* we can use linear range, but it is not necessary */
+ return (cj > 0) ? 1<<13 : -1<<13;
+ }
+
+ if (x > 0) {
+ return (cj > 0) ? atan_lut[x] : atan_lut[x] - (1<<14);
+ } else {
+ return (cj > 0) ? (1<<14) - atan_lut[-x] : -atan_lut[-x];
+ }
+
+ return 0;
+}
+
void fm_demod(struct fm_state *fm)
{
int i, pcm;
@@ -350,12 +405,19 @@ void fm_demod(struct fm_state *fm)
fm->pre_r, fm->pre_j);
fm->signal2[0] = (int16_t)pcm;
for (i = 2; i < (fm->signal_len); i += 2) {
- if (fm->custom_atan) {
+ switch (fm->custom_atan) {
+ case 0:
+ pcm = polar_discriminant(fm->signal[i], fm->signal[i+1],
+ fm->signal[i-2], fm->signal[i-1]);
+ break;
+ case 1:
pcm = polar_disc_fast(fm->signal[i], fm->signal[i+1],
fm->signal[i-2], fm->signal[i-1]);
- } else {
- pcm = polar_discriminant(fm->signal[i], fm->signal[i+1],
+ break;
+ case 2:
+ pcm = polar_disc_lut(fm->signal[i], fm->signal[i+1],
fm->signal[i-2], fm->signal[i-1]);
+ break;
}
fm->signal2[i/2] = (int16_t)pcm;
}
@@ -640,7 +702,7 @@ int main(int argc, char **argv)
fm.mode_demod = &fm_demod;
sem_init(&data_ready, 0, 0);
- while ((opt = getopt(argc, argv, "d:f:g:s:b:l:o:t:r:p:EFANWMULRD")) != -1) {
+ while ((opt = getopt(argc, argv, "d:f:g:s:b:l:o:t:r:p:EFA:NWMULRD")) != -1) {
switch (opt) {
case 'd':
dev_index = atoi(optarg);
@@ -688,7 +750,13 @@ int main(int argc, char **argv)
fm.fir_enable = 1;
break;
case 'A':
- fm.custom_atan = 1;
+ if (strcmp("std", optarg) == 0) {
+ fm.custom_atan = 0;}
+ if (strcmp("fast", optarg) == 0) {
+ fm.custom_atan = 1;}
+ if (strcmp("lut", optarg) == 0) {
+ atan_lut_init();
+ fm.custom_atan = 2;}
break;
case 'D':
fm.deemph = 1;