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Difference between revisions of "Cine/Specifications"
Added info about how to parse the source stream into bits.
(Clarification about commands' parameters.) |
(Added info about how to parse the source stream into bits.) |
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===Bit sequences in the compressed stream=== | ===Bit sequences in the compressed stream=== | ||
The whole packed data consists of commands and their parameters. | |||
The source stream is read as a bit stream. Behind the scenes it is read in one | |||
unsigned big endian 32-bit integer value at a time and when such a chunk becomes | |||
depleted of bits then another chunk is read in etc. Each chunk's least significant | |||
bit is the first bit read from it, the most significant bit is the last bit read from it etc. | |||
Because of the way the Delphine's decompressor routine handled the bit stream the first | |||
chunk acts in a sort a peculiar way. All other chunks in the source stream always contain | |||
full 32 bits but the first chunk contains only 0 to 31 bits. If the first chunk is zero, | |||
then we simply discard it and read another chunk. If the first chunk is not zero, then it | |||
contains as many source bits as its highest set bit's position is (e.g. 100b contains 2 bits | |||
because its highest set bit is at bit position 2, 110101b contains 5 bits, 1b contains 0 bits etc). | |||
So all the less significant bits than the first chunk's highest set bit are valid source stream | |||
bits (That means the highest set bit in the first chunk is always discarded). | |||
First bit of a command always tells how many bits the whole command takes. | First bit of a command always tells how many bits the whole command takes. | ||