From 22530ad1cee9002903a5a4302e6b20bd7823c445 Mon Sep 17 00:00:00 2001 From: Niklas Haas Date: Thu, 28 Sep 2023 22:14:40 +0200 Subject: [PATCH] lavc/h274: transpose IDCT 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 a5caf09564..5709200322 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); }