mirror of https://github.com/google/brotli
Merge pull request #229 from dsnet/master
Fixed minor white-space formatting and ordering of elements
This commit is contained in:
szabadka
commit
b7a613fd51
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@ -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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@ -493,35 +493,35 @@ from most- to least-significant bit. The code lengths are
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initially in tree[I].Len; the codes are produced in tree[I].Code.
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.nf
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1) Count the number of codes for each code length. Let
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bl_count[N] be the number of codes of length N, N >= 1.
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1) Count the number of codes for each code length. Let
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bl_count[N] be the number of codes of length N, N >= 1.
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2) Find the numerical value of the smallest code for each
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code length:
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2) Find the numerical value of the smallest code for each
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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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@ -1243,20 +1243,20 @@ following C language function:
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.nf
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void InverseMoveToFrontTransform(uint8_t* v, int v_len) {
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uint8_t mtf[256];
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int i;
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for (i = 0; i < 256; ++i) {
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mtf[i] = (uint8_t)i;
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}
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for (i = 0; i < v_len; ++i) {
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uint8_t index = v[i];
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uint8_t value = mtf[index];
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v[i] = value;
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for (; index; --index) {
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mtf[index] = mtf[index - 1];
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}
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mtf[0] = value;
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}
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uint8_t mtf[256];
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int i;
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for (i = 0; i < 256; ++i) {
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mtf[i] = (uint8_t)i;
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}
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for (i = 0; i < v_len; ++i) {
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uint8_t index = v[i];
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uint8_t value = mtf[index];
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v[i] = value;
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for (; index; --index) {
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mtf[index] = mtf[index - 1];
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}
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mtf[0] = value;
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}
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}
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.fi
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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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@ -1434,57 +1434,57 @@ 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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the compressed data, where the bits are parsed from
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right to left, so 0110111 has the value 12):
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the following variable length code (as it appears in
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the compressed data, where the bits are parsed from
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right to left, so 0110111 has the value 12):
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Value Bit Pattern
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----- -----------
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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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@ -1596,8 +1596,8 @@ commands. Each command has the following format:
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described in Paragraph 7.3.
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Block type code for next distance block type, appears only
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if NBLTYPESD >= 2 and the previous distance block count
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is zero
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if NBLTYPESD >= 2 and the previous distance block count
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is zero
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Block count code + Extra bits for next distance block
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length, appears only if NBLTYPESD >= 2 and the previous
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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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@ -1795,7 +1795,7 @@ available in the brotli open-source project:
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https://github.com/google/brotli
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.ti 0
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15. Acknowledgements
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15. Acknowledgments
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The authors would like to thank Mark Adler for providing helpful review
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comments, validating the specification by writing an independent decompressor
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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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|
|
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