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LibVideo/VP9: Clamp reference frame prediction coords outside loops

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Moving the clamping of the coordinates of the reference frame samples
as well as some bounds checks outside of the loop reduces the branches
needed in the `predict_inter_block()` significantly.

This results in a whopping ~41% improvement in decode performance
of an inter-prediction-heavy YouTube video (~35.4s -> ~20.8s).
This commit is contained in:
Zaggy1024 2023-04-13 14:03:02 -05:00 • committed by Tim Flynn
parent bc49af08b4
commit 08b90bb2d0
Notes: sideshowbarker 2024-07-16 22:22:13 +09:00
1 changed files with 12 additions and 5 deletions
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17
Userland/Libraries/LibVideo/VP9/Decoder.cpp
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@ -939,15 +939,19 @@ DecoderErrorOr<void> Decoder::predict_inter_block(u8 plane, BlockContext const&
return intermediate_buffer[row * width + column];
};
// Check our reference frame bounds before starting the loop.
reference_frame_buffer_at(scaled_bottom, scaled_right);
for (auto row = 0u; row < intermediate_height; row++) {
auto clamped_row = static_cast<size_t>(clip_3(0, scaled_bottom, (offset_scaled_block_y >> 4) + static_cast<i32>(row) - 3));
u16 const* scan_line = &reference_frame_buffer_at(clamped_row, 0);
for (auto column = 0u; column < width; column++) {
auto samples_start = offset_scaled_block_x + static_cast<i32>(scaled_step_x * column);
i32 accumulated_samples = 0;
for (auto t = 0u; t < 8u; t++) {
auto sample = reference_frame_buffer_at(
clip_3(0, scaled_bottom, (offset_scaled_block_y >> 4) + static_cast<i32>(row) - 3),
clip_3(0, scaled_right, (samples_start >> 4) + static_cast<i32>(t) - 3));
auto sample = scan_line[clip_3(0, scaled_right, (samples_start >> 4) + static_cast<i32>(t) - 3)];
accumulated_samples += subpel_filters[block_context.interpolation_filter][samples_start & 15][t] * sample;
}
intermediate_buffer_at(row, column) = clip_1(block_context.frame_context.color_config.bit_depth, rounded_right_shift(accumulated_samples, 7));
@ -957,11 +961,14 @@ DecoderErrorOr<void> Decoder::predict_inter_block(u8 plane, BlockContext const&
for (auto row = 0u; row < height; row++) {
for (auto column = 0u; column < width; column++) {
auto samples_start = (offset_scaled_block_y & 15) + static_cast<i32>(scaled_step_y * row);
auto const* scan_column = &intermediate_buffer_at(samples_start >> 4, column);
auto const* subpel_filters_for_samples = subpel_filters[block_context.interpolation_filter][samples_start & 15];
i32 accumulated_samples = 0;
for (auto t = 0u; t < 8u; t++) {
auto sample = intermediate_buffer_at((samples_start >> 4) + t, column);
accumulated_samples += subpel_filters[block_context.interpolation_filter][samples_start & 15][t] * sample;
auto sample = *scan_column;
accumulated_samples += subpel_filters_for_samples[t] * sample;
scan_column += width;
}
block_buffer_at(row, column) = clip_1(block_context.frame_context.color_config.bit_depth, rounded_right_shift(accumulated_samples, 7));
}