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1991-08-11
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29 lines
1. The problem was caused by an overflow in the arithmetic coder
due to long strings of repeated characters. This has been
fixed.
2. The program now tests for repeated strings and bypasses the
scan procedure. This has improved the performance significantly
for the slowest files.
3. I have included all the source files and executables. Most of
the changes are in MODEL.C. I have made some minor changes to
some of the other routines, such as correcting spelling mistakes.
4. I have checked the underflow situation at end of file, and I am
still convinced that my method works. The version of the
arithetic coding algorithm published in the CACM presents random
bits to the decoder at end of file, so that the final value output
by the coder must include enough bits to allow the final symbol
to be resolved no matter what follows. This means outputting the
underflow bits plus two more to ensure the input value is bracketed
by the high and low limits.
I get around this problem by returning zeroes after the decoder
detects end of file.
Thank you for the chance to fix the problems.
Charles.