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WebP/Lossy: Clamp negative quantization indices to zero

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The spec doesn't talk about this happening in the text, but
`dequant_init()` in 20.4 stores `q` in an int and clamps that
to 0 later.
This commit is contained in:
Nico Weber 2023-06-01 09:09:24 -04:00 • committed by Andreas Kling
parent c2ec97dd79
commit 661b2d394d
3 changed files with 24 additions and 3 deletions
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6
Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.cpp
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@ -621,7 +621,7 @@ i16 dequantize_value(i16 value, bool is_dc, QuantizationIndices const& quantizat
y_ac_base = segmentation.quantizer_update_value[segment_id];
}
u8 dequantization_index;
int dequantization_index;
if (index.is_y2())
dequantization_index = y_ac_base + (is_dc ? quantization_indices.y2_dc_delta : quantization_indices.y2_ac_delta);
else if (index.is_u() || index.is_v())
@ -631,9 +631,9 @@ i16 dequantize_value(i16 value, bool is_dc, QuantizationIndices const& quantizat
// clamp index
if ((index.is_u() || index.is_v()) && is_dc)
dequantization_index = min(dequantization_index, 117);
dequantization_index = clamp(dequantization_index, 0, 117);
else
dequantization_index = min(dequantization_index, 127);
dequantization_index = clamp(dequantization_index, 0, 127);
// "the multiplies are computed and stored using 16-bit signed integers."
i16 dequantization_factor;