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See:
Description
Class Summary | |
---|---|
ArithmeticCoder | An arithmetic coder. |
ArithmeticDecoder | An arithmetic decoder. |
ByteArrayPostingList | Lightweight posting accumulator with format similar to that generated by BitStreamIndexWriter . |
InterpolativeCoding | Static methods implementing interpolative coding. |
Bit-level I/O classes.
The standard Java API lacks bit-level I/O classes: to this purpose, MG4J
provides mg4j.io.InputBitStream
and mg4j.io.OutputBitStream
, which can wrap any standard Java
corresponding stream and make it work at the bit level; moreover, they
provide support for several useful formats (such as unary, binary, minimal
binary, γ, δ and Golomb encoding).
Compression can be achieved using self-delimiting formats supported by
the classes above, or also by arithmetic coding, using the
classes ArithmeticCoder
and ArithmeticDecoder
. Note that arithmetic coding is
not very efficient in the present implementation, as it does not allow a
varying number of symbols.
Bit input and output streams offer also efficient buffering and a way to
reposition the bit stream in case the underlying byte stream is a
file-based stream or a RepositionableStream
.
All coding methods work on natural numbers. The encoding of zero is very natural for some techniques, and much less natural for others. To keep methods rationally organised, all methods are able to encode any natural number. If, for instance, you want to write positive numbers in unary encoding and you do not want to waste a bit, you have to decrement them first (i.e., instead of p you must encode p−1).
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