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Fixed minor whitespace formatting and ordering of elements
Fixed minor whitespacing issues that caused print-out to be slightly confusing. Biggest change is in section 9.2, where an indent seemed to indicate that some fields were part of the previous field, when they were not related. Also, changed the order that transforms are described in section 8 to match the enumeration values that are explicitly defined in Appendix B.
This commit is contained in:
Joe Tsai
parent
20e838f6ad
commit
1486df764e
@ -4,7 +4,7 @@
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.lt 7.2i
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.nr LL 7.2i
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.nr LT 7.2i
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.ds LF Alakuijala & Szabadka
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.ds LF Alakuijala & Szabadka
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.ds RF FORMFEED[Page %]
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.ds LH Internet-Draft
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.ds RH October 2015
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@ -417,7 +417,7 @@ We define a prefix code in terms of a binary tree in which the two
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edges descending from each non-leaf node are labeled 0 and 1 and
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in which the leaf nodes correspond one-for-one with (are labeled
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with) the symbols of the alphabet; then the code for a symbol is
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the sequence of 0's and 1's on the edges leading from the root to
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the sequence of 0's and 1's on the edges leading from the root to
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the leaf labeled with that symbol. For example:
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.nf
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@ -436,7 +436,7 @@ the leaf labeled with that symbol. For example:
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.fi
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A parser can decode the next symbol from the compressed stream
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by walking down the tree from the root, at each step choosing the
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by walking down the tree from the root, at each step choosing the
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edge corresponding to the next compressed data bit.
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Given an alphabet with known symbol frequencies, the Huffman
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@ -500,28 +500,28 @@ initially in tree[I].Len; the codes are produced in tree[I].Code.
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code length:
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.KS
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code = 0;
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bl_count[0] = 0;
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for (bits = 1; bits <= MAX_BITS; bits++) {
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code = (code + bl_count[bits-1]) << 1;
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next_code[bits] = code;
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}
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code = 0;
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bl_count[0] = 0;
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for (bits = 1; bits <= MAX_BITS; bits++) {
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code = (code + bl_count[bits-1]) << 1;
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next_code[bits] = code;
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}
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.KE
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3) Assign numerical values to all codes, using consecutive
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values for all codes of the same length with the base
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values determined at step 2. Codes that are never used
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(which have a bit length of zero) must not be assigned a
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value.
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3) Assign numerical values to all codes, using consecutive
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values for all codes of the same length with the base
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values determined at step 2. Codes that are never used
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(which have a bit length of zero) must not be assigned a
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value.
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.KS
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for (n = 0; n <= max_code; n++) {
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len = tree[n].Len;
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if (len != 0) {
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tree[n].Code = next_code[len];
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next_code[len]++;
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}
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}
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for (n = 0; n <= max_code; n++) {
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len = tree[n].Len;
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if (len != 0) {
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tree[n].Code = next_code[len];
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next_code[len]++;
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}
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}
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.KE
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.fi
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@ -827,7 +827,7 @@ past distances as follows:
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13: second-to-last distance + 2
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14: second-to-last distance - 3
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15: second-to-last distance + 3
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.fi
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.fi
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The ring buffer of four last distances is initialized by the values
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16, 15, 11 and 4 (i.e. the fourth-to-last is set to 16, the third-to-last
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@ -887,7 +887,7 @@ integer values. The number of insert and copy extra bits can be
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Some of the insert-and-copy length codes also express the fact that
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the distance symbol of the distance in the same command is 0, i.e. the
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distance component of the command is the same as that of the previous
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command. In this case, the distance code and extra bits for the
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command. In this case, the distance code and extra bits for the
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distance are omitted from the compressed data stream.
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We describe the insert-and-copy length code alphabet in terms of the
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@ -1066,10 +1066,10 @@ p1 and p2 are initialized to zero.
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There are four methods, called context modes, to compute the
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Context ID:
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.nf
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* MSB6, where the Context ID is the value of six most
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significant bits of p1,
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* LSB6, where the Context ID is the value of six least
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significant bits of p1,
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* MSB6, where the Context ID is the value of six most
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significant bits of p1,
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* UTF8, where the Context ID is a complex function of p1, p2,
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optimized for text compression, and
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* Signed, where Context ID is a complex function of p1, p2,
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@ -1213,7 +1213,7 @@ RLEMAX + NTREES symbols:
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If RLEMAX = 0, the run length coding is not used, and the symbols
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of the alphabet are directly the values in the context map. We can
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now define the format of the context map (the same format is used
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now define the format of the context map (the same format is used
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for literal and distance context maps):
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.nf
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@ -1326,8 +1326,8 @@ where the _i subscript denotes the transform_id above. Each T_i
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is one of the following 21 elementary transforms:
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.nf
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Identity, OmitLast1, ..., OmitLast9, UppercaseFirst, UppercaseAll,
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OmitFirst1, ..., OmitFirst9
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Identity, UppercaseFirst, UppercaseAll,
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OmitFirst1, ..., OmitFirst9, OmitLast1, ..., OmitLast9
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.fi
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The form of these elementary transforms are as follows:
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@ -1335,15 +1335,15 @@ The form of these elementary transforms are as follows:
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.nf
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Identity(word) = word
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OmitLastk(word) = the first (length(word) - k) bytes of word, or
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empty string if length(word) < k
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UppercaseFirst(word) = first UTF-8 character of word upper-cased
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UppercaseAll(word) = all UTF-8 characters of word upper-cased
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OmitFirstk(word) = the last (length(word) - k) bytes of word, or
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empty string if length(word) < k
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OmitLastk(word) = the first (length(word) - k) bytes of word, or
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empty string if length(word) < k
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.fi
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For the purposes of UppercaseAll, word is parsed into UTF-8
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@ -1434,52 +1434,52 @@ meta-block is the last one. The format of the meta-block header is
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the following:
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.nf
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1 bit: ISLAST, set to 1 if this is the last meta-block
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1 bit: ISLASTEMPTY, if set to 1, the meta-block is empty;
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this field is only present if ISLAST bit is set -- if
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it is 1, then the meta-block and the brotli stream ends
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at that bit, with any remaining bits in the last byte
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of the compressed stream filled with zeros (if the
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fill bits are not zero, then the stream should be
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rejected as invalid)
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2 bits: MNIBBLES, # of nibbles to represent the uncompressed
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length, encoded as follows: if set to 3, MNIBBLES is 0,
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otherwise MNIBBLES is the value of this field plus 4.
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If MNIBBLES is 0, the meta-block is empty, i.e. it does
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not generate any uncompressed data. In this case, the
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rest of the meta-block has the following format:
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1 bit: ISLAST, set to 1 if this is the last meta-block
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1 bit: ISLASTEMPTY, if set to 1, the meta-block is empty;
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this field is only present if ISLAST bit is set -- if
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it is 1, then the meta-block and the brotli stream ends
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at that bit, with any remaining bits in the last byte
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of the compressed stream filled with zeros (if the
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fill bits are not zero, then the stream should be
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rejected as invalid)
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2 bits: MNIBBLES, # of nibbles to represent the uncompressed
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length, encoded as follows: if set to 3, MNIBBLES is 0,
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otherwise MNIBBLES is the value of this field plus 4.
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If MNIBBLES is 0, the meta-block is empty, i.e. it does
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not generate any uncompressed data. In this case, the
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rest of the meta-block has the following format:
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1 bit: reserved, must be zero
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1 bit: reserved, must be zero
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2 bits: MSKIPBYTES, # of bytes to represent metadata
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length
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2 bits: MSKIPBYTES, # of bytes to represent metadata
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length
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MSKIPBYTES x 8 bits: MSKIPLEN - 1, where MSKIPLEN is
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the number of metadata bytes; this field is
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only present if MSKIPBYTES is positive,
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otherwise MSKIPLEN is 0 (if MSKIPBYTES is
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greater than 1, and the last byte is all
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zeros, then the stream should be rejected
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as invalid)
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MSKIPBYTES x 8 bits: MSKIPLEN - 1, where MSKIPLEN is
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the number of metadata bytes; this field is
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only present if MSKIPBYTES is positive,
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otherwise MSKIPLEN is 0 (if MSKIPBYTES is
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greater than 1, and the last byte is all
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zeros, then the stream should be rejected
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as invalid)
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0 - 7 bits: fill bits until the next byte boundary,
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must be all zeros
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0 - 7 bits: fill bits until the next byte boundary,
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must be all zeros
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MSKIPLEN bytes of metadata, not part of the
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uncompressed data or the sliding window
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MSKIPLEN bytes of metadata, not part of the
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uncompressed data or the sliding window
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MNIBBLES x 4 bits: MLEN - 1, where MLEN is the length
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of the meta-block uncompressed data in bytes (if the
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number of nibbles is greater than 4, and the last
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nibble is all zeros, then the stream should be
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rejected as invalid)
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MNIBBLES x 4 bits: MLEN - 1, where MLEN is the length
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of the meta-block uncompressed data in bytes (if the
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number of nibbles is greater than 4, and the last
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nibble is all zeros, then the stream should be
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rejected as invalid)
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1 bit: ISUNCOMPRESSED, if set to 1, any bits of compressed
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data up to the next byte boundary are ignored, and
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the rest of the meta-block contains MLEN bytes of
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literal data; this field is only present if the
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ISLAST bit is not set (if the ignored bits are not
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all zeros, the stream should be rejected as invalid)
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1 bit: ISUNCOMPRESSED, if set to 1, any bits of compressed
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data up to the next byte boundary are ignored, and
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the rest of the meta-block contains MLEN bytes of
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literal data; this field is only present if the
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ISLAST bit is not set (if the ignored bits are not
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all zeros, the stream should be rejected as invalid)
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1-11 bits: NBLTYPESL, # of literal block types, encoded with
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the following variable length code (as it appears in
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@ -1531,13 +1531,13 @@ the following:
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Block count code + Extra bits for first distance block
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count, only if NBLTYPESD >= 2
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2 bits: NPOSTFIX, parameter used in the distance coding
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2 bits: NPOSTFIX, parameter used in the distance coding
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4 bits: four most significant bits of NDIRECT, to get the
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actual value of the parameter NDIRECT, left-shift
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this four bit number by NPOSTFIX bits
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4 bits: four most significant bits of NDIRECT, to get the
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actual value of the parameter NDIRECT, left-shift
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this four bit number by NPOSTFIX bits
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NBLTYPESL x 2 bits: context mode for each literal block type
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NBLTYPESL x 2 bits: context mode for each literal block type
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1-11 bits: NTREESL, # of literal prefix trees, encoded with
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the same variable length code as NBLTYPESL
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@ -1553,11 +1553,11 @@ the following:
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appears only if NTREESD >= 2, otherwise the context map
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has only zero values
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NTREESL prefix codes for literals
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NTREESL prefix codes for literals
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NBLTYPESI prefix codes for insert-and-copy lengths
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NBLTYPESI prefix codes for insert-and-copy lengths
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NTREESD prefix codes for distances
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NTREESD prefix codes for distances
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.fi
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.ti 0
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@ -1686,7 +1686,7 @@ The decoding algorithm that produces the uncompressed data is as follows:
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save previous block type
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read block count using HTREE_BLEN_I and set BLEN_I
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decrement BLEN_I
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read insert and copy length, ILEN, CLEN with HTREEI[BTYPE_I]
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read insert and copy length, ILEN, CLEN using HTREEI[BTYPE_I]
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loop for ILEN
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if BLEN_L is zero
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read block type using HTREE_BTYPE_L and set BTYPE_L
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@ -1709,9 +1709,9 @@ The decoding algorithm that produces the uncompressed data is as follows:
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read block count using HTREE_BLEN_D and set BLEN_D
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decrement BLEN_D
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compute context ID, CIDD from CLEN
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read distance code with HTREED[CMAPD[4 * BTYPE_D + CIDD]]
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read distance code using HTREED[CMAPD[4 * BTYPE_D + CIDD]]
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compute distance by distance short code substitution
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move backwards distance bytes in the uncompressed data and
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move backwards distance bytes in the uncompressed data and
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copy CLEN bytes from this position to the uncompressed
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stream, or look up the static dictionary word, transform
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the word as directed, and copy the result to the
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@ -5654,7 +5654,7 @@ length is 122,784 bytes and the zlib CRC-32 of the byte sequence is
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NDBITS := 0, 0, 0, 0, 10, 10, 11, 11, 10, 10,
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10, 10, 10, 9, 9, 8, 7, 7, 8, 7,
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7, 6, 6, 5, 5
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.fi
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.fi
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.ti 0
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Appendix B. List of word transformations
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