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Merge "doc: use two's complement explicitly for uint8->int8 conversion"

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Pascal Massimino 2016-09-07 05:53:37 +00:00 committed by Gerrit Code Review
commit dd7309e30c
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doc/webp-lossless-bitstream-spec.txt
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@ -429,6 +429,11 @@ int8 ColorTransformDelta(int8 t, int8 c) {
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A conversion from the 8-bit unsigned representation (uint8) to the 8-bit
signed one (int8) is required before calling ColorTransformDelta().
It should be performed using 8-bit two's complement (that is: uint8 range
\[128-255\] is mapped to the \[-128, -1\] range of its converted int8 value).
The multiplication is to be done using more precision (with at least
16-bit dynamics). The sign extension property of the shift operation
does not matter here: only the lowest 8 bits are used from the result,