Thank you for your detailed explanation! :)
Ronald S. Bultje <rsbul...@gmail.com> 于2024年12月5日周四 20:38写道：
> Hi,
>
> Christophe asked me to chime in.
>
> On Wed, Dec 4, 2024 at 4:14 AM <uk7b-at-foxmail....@ffmpeg.org> wrote:
>
> > --- a/tests/checkasm/rv40dsp.c
> > +++ b/tests/checkasm/rv40dsp.c
> > @@ -27,7 +27,7 @@
> > #define randomize_buffers() \
> > do { \
> > for (int i = 0; i < 16*18*2; i++) \
> > - src[i] = rnd() & 0x3; \
> > + src[i] = rnd() & 0xff; \
> > } while (0)
> >
> > static void check_chroma_mc(void)
> >
>
> This is correct.
>
>
> > @@ -47,8 +47,8 @@ static void check_chroma_mc(void)
> > #define CHECK_CHROMA_MC(name)
> > \
> > do {
> > \
> > if (check_func(h.name## <http://h.name#%23> <
> http://h.name#%23>
> > _pixels_tab[size], #name "_mc%d", 1 << (3 - size))) { \
> > - for (int x = 0; x < 2; x++) {
> > \
> > - for (int y = 0; y < 2; y++) {
> > \
> > + for (int x = 0; x < 8; x++) {
> > \
> > + for (int y = 0; y < 8; y++) {
> > \
> > memcpy(dst0, src, 16 * 18);
> > \
> > memcpy(dst1, src, 16 * 18);
> > \
> > call_ref(dst0, src, 16, 16, x, y);
> > \
> > --
> > 2.47.1
> >
>
> This is theoretically correct, but it's very inefficient. If you look at
> the x86 mc8 mmx, for example, you'll notice that there's 3 codepaths: one
> for x==0&&y==0 (no subpel), one for 1D filtering (mx!=0 ^ my!=0) and one
> for 2D filtering. It can also be implemented branchless (I believe that's
> what mc4 does). But it's highly unusual to have special codepaths for mx=3
> vs. mx=4, for example.
>
> So the optimal way to test this is to keep the original loop, but add the
> following:
> for (int x = 0, mx = 0; x < 2; x++, mx = 1 + (rnd() % 7)) {
> for (int y = 0, my = 0; y < 2; y++, my = 1 + (rnd() % 7)) {
> [..]
> cal_ref(dst0, src, 16, 16, mx, my);
> [..]
> }
> }
>
> This limits the number of tests to 4, while still covering all cases over
> multiple checkasm runs, which is the correct way to test this.
>
> Ronald
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