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Data Compression
Criteria
Survey Formats
Basics
Compression Methods
Data Formats
Arithmetic Coding (AC)
Principle of the AC
General Algorithm
Encoding
Decoding
Calculation of Intervals
Division
Rounding Errors
Shifting of Intervals
AC versus Huffman
Data with high Redundancy
Adaptive AC
Implementations
Glossary
Index
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Division of the Intervals
The calculation of the sub-intervals is processed according to the following rules:
- The entire, current interval Jcurr is defined by its size, the lower and the upper endpoint:
Jcurrs, Jcurrl, Jcurru
- The sub-interval of the first symbol (0) of the alphabet starts with a closed lower endpoint at the beginning of the current interval:
Jl(0) = Jcurrl
- The open upper endpoint of the first sub-interval results from the probability of the first symbol p(0) and the size of the current interval:
Ju(0) = Jl(0) + Jcurrs * p(0)
- The closed upper endpoint of each sub-interval is equal to the closed lower endpoint of sub-interval immediately following:
Ju(x) = Jl(x+1)
- For all further sub-interval applies:
J(x) = [ Ju(x-1); Ju(x-1) + Jgess * p(x) )
- The sub-interval of the last symbol of the alphabet J(max) ends at the open upper endpoint of the current interval:
Ju(z) = Jcurru
Example "abcd":

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