NAME

Data::BitStream::Code::GammaGolomb - A Role implementing Gamma-Golomb codes

VERSION

version 0.03

DESCRIPTION

A role written for Data::BitStream that provides get and set methods for Gamma-Golomb codes. The role applies to a stream object.

Gamma-Golomb codes are basically Golomb codes using the Elias Gamma code for the quotient instead of a Unary code. This makes them suitable for occasional large outliers that would otherwise use thousands or millions of bits to encode.

In particular, the GammaGolomb(3) code is interesting for some distributions.

METHODS

Provided Object Methods

put_gammagolomb($m, $value)

put_gammagolomb($m, @values)

Insert one or more values as Gamma-Golomb codes with parameter m. Returns 1.

get_gammagolomb($m)

get_gammagolomb($m, $count)

Decode one or more Gamma-Golomb codes from the stream. If count is omitted, one value will be read. If count is negative, values will be read until the end of the stream is reached. In scalar context it returns the last code read; in array context it returns an array of all codes read.

Parameters

The parameter m must be an integer greater than or equal to 1.

The quotient of value / m is encoded using an Elias Gamma code, followed by the remainder in truncated binary form.

Note: if m == 1 then the result will be coded purely using gamma coding.

Note: if m is a power of 2 (m = 2^k for some non-negative integer k), then the result is equal to the simpler ExpGolomb(k) code, where the operations devolve into a shift and mask.

Required Methods

put_golomb

put_gamma

get_golomb

get_gamma

These methods are required for the role.

SEE ALSO

Data::BitStream::Code::Golomb

Data::BitStream::Code::Rice

Data::BitStream::Code::ExponentialGolomb

http://en.wikipedia.org/wiki/Exponential-Golomb_coding

S.W. Golomb, "Run-length encodings", IEEE Transactions on Information Theory, vol 12, no 3, pp 399-401, 1966.

R.F. Rice and R. Plaunt, "Adaptive Variable-Length Coding for Efficient Compression of Spacecraft Television Data", IEEE Transactions on Communications, vol 16, no 9, pp 889-897, Dec. 1971.

AUTHORS

Dana Jacobsen <dana@acm.org>

COPYRIGHT

Copyright 2011 by Dana Jacobsen <dana@acm.org>

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.