From: Niklas Haas <g...@haasn.dev> This naive hist[p[x]]++ loop suffers badly when there are large regions of identical values in the image, because of store-to-load forwarding delay.
Splitting up the histogram into four "parallel" histograms and processing them one at a time speeds things up significantly, about 40% on my end. --- libavfilter/vf_thumbnail.c | 71 ++++++++++++++++++++++++++++++-------- 1 file changed, 57 insertions(+), 14 deletions(-) diff --git a/libavfilter/vf_thumbnail.c b/libavfilter/vf_thumbnail.c index aff25d19c5..8cda7b45f1 100644 --- a/libavfilter/vf_thumbnail.c +++ b/libavfilter/vf_thumbnail.c @@ -27,6 +27,7 @@ * @see http://notbrainsurgery.livejournal.com/29773.html */ +#include "libavutil/intreadwrite.h" #include "libavutil/mem.h" #include "libavutil/opt.h" #include "libavutil/pixdesc.h" @@ -145,6 +146,59 @@ static AVFrame *get_best_frame(AVFilterContext *ctx) return picref; } +static void get_hist8(int *hist, const uint8_t *p, ptrdiff_t stride, + ptrdiff_t width, ptrdiff_t height) +{ + int shist[4][256] = {0}; + + const int width4 = width & ~3; + while (height--) { + for (int x = 0; x < width4; x += 4) { + const uint32_t v = AV_RN32(&p[x]); + shist[0][(uint8_t) (v >> 0)]++; + shist[1][(uint8_t) (v >> 8)]++; + shist[2][(uint8_t) (v >> 16)]++; + shist[3][(uint8_t) (v >> 24)]++; + } + /* handle tail */ + for (int x = width4; x < width; x++) + hist[p[x]]++; + p += stride; + } + + for (int i = 0; i < 4; i++) { + for (int j = 0; j < 256; j++) + hist[j] += shist[i][j]; + } +} + +static void get_hist16(int *hist, const uint8_t *p, ptrdiff_t stride, + ptrdiff_t width, ptrdiff_t height, int shift) +{ + int shist[4][256] = {0}; + + const int width4 = width & ~3; + while (height--) { + const uint16_t *p16 = (const uint16_t *) p; + for (int x = 0; x < width4; x += 4) { + const uint64_t v = AV_RN64(&p16[x]); + shist[0][(uint8_t) (v >> (shift + 0))]++; + shist[1][(uint8_t) (v >> (shift + 16))]++; + shist[2][(uint8_t) (v >> (shift + 32))]++; + shist[3][(uint8_t) (v >> (shift + 48))]++; + } + /* handle tail */ + for (int x = width4; x < width; x++) + hist[p16[x]]++; + p += stride; + } + + for (int i = 0; i < 4; i++) { + for (int j = 0; j < 256; j++) + hist[j] += shist[i][j]; + } +} + static int do_slice(AVFilterContext *ctx, void *arg, int jobnr, int nb_jobs) { ThumbContext *s = ctx->priv; @@ -204,22 +258,11 @@ static int do_slice(AVFilterContext *ctx, void *arg, int jobnr, int nb_jobs) const ptrdiff_t linesize = frame->linesize[plane]; const int planewidth = s->planewidth[plane]; int *hhist = hist + 256 * plane; - if (s->bitdepth > 8) { - const uint16_t *p16 = (const uint16_t *) p; - const int shift = s->bitdepth - 8; - - for (int j = slice_start; j < slice_end; j++) { - for (int i = 0; i < planewidth; i++) - hhist[(p16[i] >> shift) & 0xFF]++; - p16 += linesize >> 1; - } + get_hist16(hhist, p, linesize, planewidth, slice_end - slice_start, + s->bitdepth - 8); } else { - for (int j = slice_start; j < slice_end; j++) { - for (int i = 0; i < planewidth; i++) - hhist[p[i]]++; - p += linesize; - } + get_hist8(hhist, p, linesize, planewidth, slice_end - slice_start); } } break; -- 2.49.0 _______________________________________________ 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".
