I was trying to optimize this in another language (failed so far), but
did notice that it could be refreshed a bit for C, as it computes
sqrt(2) * sqrt(2) / 2 which can be simplified.
Saves 960 * sizeof(float) - 960 * sizeof(char) = 2880 bytes
The pilot_lut[] table was checked using both original and modified
versions and all 640 values come out the same.
diff -ruN freetel-code-orig/codec2-dev/src/fdmdv.c
freetel-code-new/codec2-dev/src/fdmdv.c
--- freetel-code-orig/codec2-dev/src/fdmdv.c 2014-11-17 08:50:17.912563270
-0600
+++ freetel-code-new/codec2-dev/src/fdmdv.c 2014-11-17 09:27:37.924497085
-0600
@@ -666,8 +666,8 @@
\*---------------------------------------------------------------------------*/
-void generate_pilot_fdm(COMP *pilot_fdm, int *bit, float *symbol,
- float *filter_mem, COMP *phase, COMP *freq)
+void generate_pilot_fdm(COMP *pilot_fdm, char *bit, char *symbol,
+ int *filter_mem, COMP *phase, COMP *freq)
{
int i,j,k;
float tx_baseband[M];
@@ -675,17 +675,13 @@
/* +1 -1 +1 -1 DBPSK sync carrier, once filtered becomes (roughly)
two spectral lines at +/- RS/2 */
- if (*bit)
- *symbol = -*symbol;
-
- if (*bit)
- *bit = 0;
- else
- *bit = 1;
+ *symbol = (*bit) ? -*symbol : *symbol;
+ *bit = !*bit;
/* filter DPSK symbol to create M baseband samples */
- filter_mem[NFILTER-1] = (sqrtf(2)/2) * *symbol;
+ filter_mem[NFILTER-1] = *symbol;
+
for(i=0; i<M; i++) {
tx_baseband[i] = 0.0;
for(j=M-1,k=M-i-1; j<NFILTER; j+=M,k+=M)
@@ -698,7 +694,7 @@
filter_mem[i] = filter_mem[i+M];
for(i=NFILTER-M; i<NFILTER; i++)
- filter_mem[i] = 0.0;
+ filter_mem[i] = 0;
/* upconvert */
@@ -723,15 +719,15 @@
void generate_pilot_lut(COMP pilot_lut[], COMP *pilot_freq)
{
- int pilot_rx_bit = 0;
- float pilot_symbol = sqrtf(2.0);
COMP pilot_phase = {1.0, 0.0};
- float pilot_filter_mem[NFILTER];
COMP pilot[M];
- int i,f;
+ int pilot_rx_bit = 0;
+ int i, f;
+ char pilot_symbol = 1;
+ char pilot_filter_mem[NFILTER];
for(i=0; i<NFILTER; i++)
- pilot_filter_mem[i] = 0.0;
+ pilot_filter_mem[i] = 0;
/* discard first 4 symbols as filter memory is filling, just keep
last four symbols */
------------------------------------------------------------------------------
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