On Thu, 28 Sep 2023 23:08:48 +0200 Niklas Haas <ffm...@haasn.xyz> wrote:
> From: Niklas Haas <g...@haasn.dev>
>
> This is mathematically equivalent to what we were doing before, but
> gives subtly different results due to rounding (rows first vs columns
> first). Doing it this way makes our film grain database generation match
> reference implementation and now produces bit-exact outputs in my
> testing.
>
> Rename the transposed variables to be a bit less confusing.
> ---
> libavcodec/h274.c | 20 ++++++++++----------
> 1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/libavcodec/h274.c b/libavcodec/h274.c
> index a5caf09564d..5709200322e 100644
> --- a/libavcodec/h274.c
> +++ b/libavcodec/h274.c
> @@ -59,13 +59,13 @@ static void init_slice_c(int8_t out[64][64], uint8_t h,
> uint8_t v,
> //
> // Note: To make the subsequent matrix multiplication cache friendlier,
> we
> // store each *column* of the starting image in a *row* of `out`
> - for (int y = 0; y <= freq_v; y++) {
> - for (int x = 0; x <= freq_h; x += 4) {
> + for (int l = 0; l <= freq_v; l++) {
> + for (int k = 0; k <= freq_h; k += 4) {
> uint16_t offset = seed % 2048;
> - out[x + 0][y] = Gaussian_LUT[offset + 0];
> - out[x + 1][y] = Gaussian_LUT[offset + 1];
> - out[x + 2][y] = Gaussian_LUT[offset + 2];
> - out[x + 3][y] = Gaussian_LUT[offset + 3];
> + out[l][k + 0] = Gaussian_LUT[offset + 0];
> + out[l][k + 1] = Gaussian_LUT[offset + 1];
> + out[l][k + 2] = Gaussian_LUT[offset + 2];
> + out[l][k + 3] = Gaussian_LUT[offset + 3];
> prng_shift(&seed);
> }
> }
> @@ -74,9 +74,9 @@ static void init_slice_c(int8_t out[64][64], uint8_t h,
> uint8_t v,
>
> // 64x64 inverse integer transform
> for (int y = 0; y < 64; y++) {
> - for (int x = 0; x <= freq_h; x++) {
> + for (int x = 0; x <= freq_v; x++) {
> int32_t sum = 0;
> - for (int p = 0; p <= freq_v; p++)
> + for (int p = 0; p <= freq_h; p++)
> sum += R64T[y][p] * out[x][p];
> tmp[y][x] = (sum + 128) >> 8;
> }
> @@ -85,8 +85,8 @@ static void init_slice_c(int8_t out[64][64], uint8_t h,
> uint8_t v,
> for (int y = 0; y < 64; y++) {
> for (int x = 0; x < 64; x++) {
> int32_t sum = 0;
> - for (int p = 0; p <= freq_h; p++)
> - sum += tmp[y][p] * R64T[x][p]; // R64T^T = R64
> + for (int p = 0; p <= freq_v; p++)
> + sum += tmp[x][p] * R64T[y][p]; // R64T^T = R64
> // Renormalize and clip to [-127, 127]
> out[y][x] = av_clip((sum + 128) >> 8, -127, 127);
> }
> --
> 2.42.0
>
Merged as 22530ad1ce
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