"Fossies" - the Fresh Open Source Software Archive  

Source code changes of the file "libburn/ecma130ab.c" between
xorriso-1.5.2.tar.gz and xorriso-1.5.4.tar.gz

About: GNU xorriso creates, loads, manipulates and writes ISO 9660 filesystem images with Rock Ridge extensions. It is suitable for incremental data backup and for production of bootable ISO 9660 images. GNU xorriso is a statical compilation of the libraries libburn, libisofs, libisoburn, and libjte.

ecma130ab.c  (xorriso-1.5.2):ecma130ab.c  (xorriso-1.5.4)
skipping to change at line 77 skipping to change at line 77
The P-parity bytes of each column get reunited as LSB and MSB of two words. The P-parity bytes of each column get reunited as LSB and MSB of two words.
word1 gets written to positions 1032 to 1074, word0 to 1075 to 1117. word1 gets written to positions 1032 to 1074, word0 to 1075 to 1117.
The Q-parity bytes of each diagonal get reunited too. word1 goes to 1118 The Q-parity bytes of each diagonal get reunited too. word1 goes to 1118
to 1143, word0 to 1144 to 1169. to 1143, word0 to 1144 to 1169.
>>> I do not read this swap of word1 and word0 from ECMA-130 Annex A. >>> I do not read this swap of word1 and word0 from ECMA-130 Annex A.
>>> But the new output matches the old output only if it is done that way. >>> But the new output matches the old output only if it is done that way.
>>> See correctness reservation below. >>> See correctness reservation below.
Algebra on Galois fields is the same as on Rational Numbers. Algebra on Galois fields is the same as on Rational Numbers.
But arithmetics is defined by operations on polynomials rather than the But arithmetics on its polynomials differ from usual integer arithmetics
usual integer arithmetics on binary numbers. on binary numbers.
Addition and subtraction are identical with the binary exor operator. Addition and subtraction are identical with the binary exor operator.
Multiplication and division would demand polynomial division, e.g. by the Multiplication and division would demand polynomial division, e.g. by the
euclidian algorithm. The computing path over logarithms and powers follows euclidean algorithm. The computing path over logarithms and powers follows
algebra and reduces the arithmetic task to table lookups, additions algebra and reduces the arithmetic task to table lookups, additions
modulo 255, and exor operations. Note that the logarithms are natural modulo 255, and exor operations. Note that the logarithms are natural
numbers, not polynomials. They get added or subtracted by the usual addition numbers, not polynomials. They get added or subtracted by the usual addition
(not by exor) and their polynomial power depends on their value modulo 255. (not by exor) and their polynomial power depends on their value modulo 255.
Needed are a logarithm table and a power table (or inverse logarithm table) Needed are a logarithm table and a power table (or inverse logarithm table)
for Galois Field GF(2^8) which will serve to perform the peculiar for Galois Field GF(2^8) which will serve to perform the peculiar
multiplication and division operation of Galois fields. multiplication and division operation of Galois fields.
The power table is simply an enumeration of x^n accorting to The power table is simply an enumeration of x^n accorting to
 End of changes. 2 change blocks. 
3 lines changed or deleted 3 lines changed or added

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