On Thu, Feb 6, 2014 at 5:31 PM, Tom Tsou <t...@tsou.cc> wrote: > On Thu, Feb 6, 2014 at 11:58 AM, Douglas Geiger > <doug.gei...@bioradiation.net> wrote: >> I'll suggest that the generic kernel should be trusted to do the correct >> thing, or at least have the correct set of intentions, and that if you want >> to change the behavior of the generic kernel, that you are introducing a >> change that will break applications depending on this behavior. >> >> I believe the use of casting the subtraction before the comparison (where: >> ((int16_t) (src0[i] - src0[i + 1]) > 0) ? src0[i] : src0[i+1]; is the full >> comparison) was intentional to ensure overflow subtraction vs. saturation >> subtraction. > > Assuming this kernel is used for some type of trellis decoding, the > overflow makes sense as it avoids the need for normalization of > accumulated metrics. It does, however, require that the spread of > input values be bounded for it to work. Otherwise, you have > comparisons between overflow values and non-overflow values, which > makes the comparison ambiguous and the output not-sane. > > -TT
Yeah, Nathan emailed me back off-list and explained that to me. Makes sense now. Thanks, Tom _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
