On Wed, Oct 25, 2023 at 8:39 PM Tomas Härdin <g...@haerdin.se> wrote:
> > > if (c) { > > e[0] = 1 << 14; > > e[1] = 0 << 14; > > e[2] = v[1]; > > e[3] = v[0]; > > } else { > > e[0] = v[0]; > > e[1] = v[1]; > > e[2] = 0 << 14; > > e[3] = 1 << 14; > > } > > > > if (invert2x2(e, d)) { > > sum = UINT64_MAX; > > goto next; > > } > > > > You can make use of the properties of e to simplify calculating the > inverse. The determinant is always v[0]<<14, so you can just do if > (!v[0]) continue; and skip the determinant check altogether. > Even for real 2x2 matrix case? (Once one of rows is not 1, 0) ? May added such cases later. > > > if (d[i] != av_clip_intp2(d[i], 15)) { > > d[i] < INT16_MIN || d[i] > INT16_MAX is more clear and probably faster > > > + lt = ((lm * e[0]) >> 14) + ((rm * e[1]) >> 14); > > + rt = ((lm * e[2]) >> 14) + ((rm * e[3]) >> 14); > > Result is implementation-defined. Use division by (1<<14). Also add > then divide. The intermediate result is 49 bits so fits easily in 64 > bits. > > You could also simplify this calculation by again making use of the > properties of e. > > > if (c) > > v += FFABS(rt); > > else > > v += FFABS(lt); > > sum += v; > > if (sum > best_sum) > > goto next; > > Seems like this reduces to solving a linear program. > > > if ((((lt * d[0]) >> 14) + ((rt * d[1]) >> 14)) > > != lm) { > > sum = UINT64_MAX; > > goto next; > > } > > > > if ((((lt * d[2]) >> 14) + ((rt * d[3]) >> 14)) > > != rm) { > > sum = UINT64_MAX; > > goto next; > > } > > Looks like a massive hack. I'd prefer to formally verify that the > arithmetic works out. Also again you can make use of the properties of > e, or inv(e) as it were. > > /Tomas > > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > To unsubscribe, visit link above, or email > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".