Hi Steve, 1/ While not strictly necessary, the sqrt(2)/2 sets the BPSK pilot power to the same level as the actual tx modem signal. I imagine the call to sqrt() it's compiled out anyway, and its in the run-once init code, not real time.
BTW as part of the software QA I ensure that the C code exactly matches the reference Octave code that was used to develop the modem. So any changes to the C modem code need to mirrored in Octave, and unit tests run to ensure thy match, plus probably performance tests (i.e. a few BER points) of the modem to ensure nothing has broken. I can show you how to do this if you like. It's really really easy to have a bug sneak in, have done it many times myself! Hence my careful testing. 2/ Re use of the question mark operator I prefer to be explicit in the C code and use if/(thens). I would assume in a modern C compiler that there would be no efficiency gain in using ?, and (for me at least) it makes the code harder to read. I don't mind the ! operator for inverting ints. 3/ The use of a char to save storage for filter_mem[] is an interesting one. Looking at the code ...... OK this function is called at init time, and the memory used for filter_mem[] is allocated just temporarily from the stack, then returned to it before run time. Thanks, David On 18/11/14 02:44, Steve wrote: > 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. > > > > ------------------------------------------------------------------------------ > Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server > from Actuate! Instantly Supercharge Your Business Reports and Dashboards > with Interactivity, Sharing, Native Excel Exports, App Integration & more > Get technology previously reserved for billion-dollar corporations, FREE > http://pubads.g.doubleclick.net/gampad/clk?id=157005751&iu=/4140/ostg.clktrk > > > > _______________________________________________ > Freetel-codec2 mailing list > Freetel-codec2@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=157005751&iu=/4140/ostg.clktrk _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
