Re: ANCI-C vs Gnuradio/C++ speeeed


#1

Al,

the encoder IS NOT the bottleneck in this communication system.
It is the Viterbi Algorithm that is responsible for 80%-90%
of the overall time.

Achilleas

=============================================

You are returning a vector by value:
from fsm.h:
//========
std::vector NS () const { return d_NS; }
std::vector OS () const { return d_OS; }
std::vector PS () const { return d_PS; }
std::vector PI () const { return d_PI; }
//========

inside a loop, double nested:
from: howto_trellis_encoder_si.cc

for (int m=0;m<nstreams;m++) {
// stuff deleted
for (int i = 0; i < noutput_items; i++){
out[i] = (int) d_FSM.OS()[d_ST_tmpd_FSM.I()+in[i]];
d_ST_tmp = (int) d_FSM.NS()[d_ST_tmp
d_FSM.I()+in[i]];
}

I am amazed that you are only getting a 5-fold reduction!

A few years ago, I made some tests, in gnucap. I found that in
all tests there was no run time speed penalty for using STL,
even in speed critical tight loops. By using it, I was able to
do things that would have been impractical without it,
resulting in a net speed improvement. Compiling is slower, but
I can live with that.