[FFmpeg-devel] Performances improvement in "image_copy_plane"

[Marco Vianini <marco_vianini-at-yahoo.it@ffmpeg.org>]

 You can get a very big improvement of performances in the special (but very likely) case of: "(dst_linesize == bytewidth && src_linesize == bytewidth)"

In this case in fact We can "Coalesce rows", that is using ONLY ONE MEMCPY, instead of a smaller memcpy for every row (that is looping for height times).

Code:"static void image_copy_plane(uint8_t       *dst, ptrdiff_t dst_linesize,                             const uint8_t *src, ptrdiff_t src_linesize,                             ptrdiff_t bytewidth, int height){    if (!dst || !src)        return;    av_assert0(abs(src_linesize) >= bytewidth);    av_assert0(abs(dst_linesize) >= bytewidth); // MY PATCH START    // Coalesce rows.    if (dst_linesize == bytewidth && src_linesize == bytewidth) {      bytewidth *= height;      height = 1;      src_linesize = dst_linesize = 0;    }// MY PATCH STOP
    for (;height > 0; height--) {        memcpy(dst, src, bytewidth);        dst += dst_linesize;        src += src_linesize;    }}"
What do You think about?Thank You
Marco Vianini
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