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Spec clarifications for Section 8. 

Based on Mark Adler's review comments.
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Zoltan Szabadka 2015-04-08 11:07:00 +02:00
parent 8618383b9b
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2 changed files with 525 additions and 466 deletions
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docs/draft-alakuijala-brotli-02.nroff
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@ -1106,7 +1106,7 @@ The number of static dictionary words for a given length is:
.nf .nf
NWORDS[length] = 0 (if length < 4) NWORDS[length] = 0 (if length < 4)
NWORDS[length] = (1 << NDBITS[lengths]) (if length >= 4) NWORDS[length] = (1 << NDBITS[length]) (if length >= 4)
.fi .fi
DOFFSET and DICTSIZE are defined by the following recursion: DOFFSET and DICTSIZE are defined by the following recursion:
@ -1122,7 +1122,7 @@ index is:
offset(length, index) = DOFFSET[length] + index * length offset(length, index) = DOFFSET[length] + index * length
Each static dictionary word has NTRANSFORMS different forms, given by Each static dictionary word has 121 different forms, given by
applying a word transformation to a base word in the DICT array. The applying a word transformation to a base word in the DICT array. The
list of word transformations is given in Appendix B. The static list of word transformations is given in Appendix B. The static
dictionary word for a <length, distance> pair can be reconstructed as dictionary word for a <length, distance> pair can be reconstructed as
@ -1131,21 +1131,21 @@ follows:
.nf .nf
word_id = distance - (max allowed distance + 1) word_id = distance - (max allowed distance + 1)
index = word_id % NWORDS[length] index = word_id % NWORDS[length]
base_word = DICT[offset(length, index)..offset(length, index+1)) base_word = DICT[offset(length, index)..offset(length, index+1)-1]
transform_id = word_id >> NDBITS[length] transform_id = word_id >> NDBITS[length]
.fi .fi
The string copied to the output stream is computed by applying the The string copied to the output stream is computed by applying the
transformation to the base dictionary word. If transform_id is transformation to the base dictionary word. If transform_id is
greater than NTRANSFORMS - 1 or length is greater than 24, the greater than 120 or length is greater than 24, the
compressed data set is invalid. compressed data set is invalid.
Each word transformation has the follwing form: Each word transformation has the following form:
transform_i(word) = prefix_i + T_i(word) + suffix_i transform_i(word) = prefix_i + T_i(word) + suffix_i
where the _i subscript denotes the transform_id above. Each T_i where the _i subscript denotes the transform_id above. Each T_i
is one of the following 20 elementary transforms: is one of the following 21 elementary transforms:
.nf .nf
Identity, OmitLast1, ..., OmitLast9, UppercaseFirst, UppercaseAll, Identity, OmitLast1, ..., OmitLast9, UppercaseFirst, UppercaseAll,
@ -1169,7 +1169,7 @@ The form of these elementary transforms are as follows:
.fi .fi
For the purposes of UppercaseAll, word is parsed into UTF-8 For the purposes of UppercaseAll, word is parsed into UTF-8
characters an coverted to upper-case by taking 1 - 3 bytes at a time, characters and converted to upper-case by taking 1 - 3 bytes at a time,
using the algorithm below: using the algorithm below:
.nf .nf
@ -1196,6 +1196,9 @@ executed only once.
Appendix B. contains the list of transformations by specifying the Appendix B. contains the list of transformations by specifying the
prefix, elementary transform and suffix components of each of them. prefix, elementary transform and suffix components of each of them.
Note that the OmitFirst8 elementary transform is not used in the list
of transformations. The strings in Appendix B. are in C string format
with respect to escape (backslash) characters.
.ti 0 .ti 0
9. Compressed data format 9. Compressed data format

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docs/draft-alakuijala-brotli-02.txt
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