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WebP/Lossy: Remove an unnecessary branch

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`predicted_y_above` is initialized to a row of 127s, so we can just
read from it even in the first macroblock row.

No behavior change.
This commit is contained in:
Nico Weber 2023-05-31 08:37:48 -04:00 • committed by Andreas Kling
parent 47d1b45583
commit 40e1ec6cf9
1 changed files with 4 additions and 7 deletions
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11
Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.cpp
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@ -1068,7 +1068,7 @@ void process_macroblock(Span<i16> output, IntraMacroblockMode mode, int mb_x, in
add_idct_to_prediction<4 * N>(output, coefficients_array[i], x, y);
}
void process_subblocks(Span<i16> y_output, MacroblockMetadata const& metadata, int mb_x, int mb_y, ReadonlySpan<i16> predicted_y_left, ReadonlySpan<i16> predicted_y_above, i16 y_truemotion_corner, Coefficients coefficients_array[], int macroblock_width)
void process_subblocks(Span<i16> y_output, MacroblockMetadata const& metadata, int mb_x, ReadonlySpan<i16> predicted_y_left, ReadonlySpan<i16> predicted_y_above, i16 y_truemotion_corner, Coefficients coefficients_array[], int macroblock_width)
{
// Loop over the 4x4 subblocks
for (int y = 0, i = 0; y < 4; ++y) {
@ -1095,11 +1095,8 @@ void process_subblocks(Span<i16> y_output, MacroblockMetadata const& metadata, i
for (int i = 0; i < 8; ++i) {
if (x == 3 && i >= 4) { // rightmost subblock, 4 right pixels?
if (mb_x == macroblock_width - 1) { // rightmost macroblock
if (mb_y == 0) { // topmost macroblock row
above[i] = 127;
} else {
above[i] = predicted_y_above[mb_x * 16 + 4 * x + 3];
}
// predicted_y_above is initialized to 127 above the first row, so no need for an explicit branch for mb_y == 0.
above[i] = predicted_y_above[mb_x * 16 + 4 * x + 3];
} else {
above[i] = predicted_y_above[mb_x * 16 + 4 * x + i];
}
@ -1193,7 +1190,7 @@ ErrorOr<void> decode_VP8_image_data(Gfx::Bitmap& bitmap, FrameHeader const& head
i16 y_data[16 * 16] {};
if (metadata.intra_y_mode == B_PRED)
process_subblocks(y_data, metadata, mb_x, mb_y, predicted_y_left, predicted_y_above, y_truemotion_corner, coefficients.y_coeffs, macroblock_width);
process_subblocks(y_data, metadata, mb_x, predicted_y_left, predicted_y_above, y_truemotion_corner, coefficients.y_coeffs, macroblock_width);
else
process_macroblock<4>(y_data, metadata.intra_y_mode, mb_x, mb_y, predicted_y_left, predicted_y_above, y_truemotion_corner, coefficients.y_coeffs);