src.it.unimi.dsi.big.mg4j.io.package.html Maven / Gradle / Ivy
Show all versions of mg4j-big Show documentation
MG4J: Managing Gigabytes for Java
Bit-level I/O classes.
Package Specification
The standard Java API lacks bit-level I/O classes: to this purpose, MG4J
provides {@link it.unimi.dsi.big.mg4j.io.InputBitStream} and {@link
it.unimi.dsi.big.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 {@link it.unimi.dsi.big.mg4j.io.ArithmeticCoder} and {@link
it.unimi.dsi.big.mg4j.io.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 {@link it.unimi.dsi.fastutil.io.RepositionableStream}.
Conventions
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).