5.3 The range decoder

The LZMA stream is consumed one byte at a time by the range decoder. (See ‘normalize’ in the source). Every byte consumed produces a variable number of decoded bits, depending on how well these bits agree with their context. (See ‘decode_bit’ in the source).

The range decoder state consists of two unsigned 32-bit variables, range (representing the most significant part of the range size not yet decoded), and code (representing the current point within range). range is initialized to (2^32 - 1), and code is initialized to 0.

The range encoder produces a first 0 byte that must be ignored by the range decoder. This is done by shifting 5 bytes in the initialization of code instead of 4. (See the ‘Range_decoder’ constructor in the source).

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