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Updates to Brotli compression format, decoder and encoder

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This commit contains a batch of changes that were made to the Brotli
compression algorithm in the last month. Most important changes:

   * Fixes to the spec.
   * Change of code length code order.
   * Use a 2-level Huffman lookup table in the decoder.
   * Faster uncompressed meta-block decoding.
   * Optimized encoding of the Huffman code.
   * Detection of UTF-8 input encoding.
   * UTF-8 based literal cost modeling for improved
     backward reference selection.
This commit is contained in:
Zoltan Szabadka
2014-02-14 15:04:23 +01:00
parent dfc5a9f215
commit cbd5cb55f4
16 changed files with 912 additions and 635 deletions
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brotli/brotlispec.txt
+13 -12
View File
@@ -498,11 +498,11 @@ Abstract
Symbol Code
------ ----
0 00
1 1010
2 100
3 11
4 01
5 1011
1 1110
2 110
3 01
4 10
5 1111
We can now define the format of the complex Huffman code as
follows:
@@ -513,7 +513,7 @@ Abstract
Code lengths for symbols in the code length alphabet given
just above, in the order: 1, 2, 3, 4, 0, 17, 5, 6, 16, 7,
just above, in the order: 1, 2, 3, 4, 0, 5, 17, 6, 16, 7,
8, 9, 10, 11, 12, 13, 14, 15
The code lengths of code length symbols are between 0 and
@@ -572,7 +572,7 @@ Abstract
6: last distance - 2
7: last distance + 2
8: last distance - 3
9: last disatnce + 3
9: last distance + 3
10: second last distance - 1
11: second last distance + 1
12: second last distance - 2
@@ -647,7 +647,7 @@ Abstract
---- ---- ------ ---- ---- ------- ---- ---- -------
0 0 0 8 2 10-13 16 6 130-193
1 0 1 9 2 14-17 17 7 194-321
2 0 2 10 3 18-25 18 8 322-527
2 0 2 10 3 18-25 18 8 322-577
3 0 3 11 3 26-33 19 9 578-1089
4 0 4 12 4 34-49 20 10 1090-2113
5 0 5 13 4 50-65 21 12 2114-6209
@@ -681,7 +681,7 @@ Abstract
| | |
+---------+---------+---------+
| | | |
0-7 | 128-191 | 192-255 | 383-447 |
0-7 | 128-191 | 192-255 | 384-447 |
| | | |
+---------+---------+---------+
| | | |
@@ -689,7 +689,7 @@ Abstract
| | | |
+---------+---------+---------+
| | | |
16-23 | 448-551 | 576-639 | 640-703 |
16-23 | 448-511 | 576-639 | 640-703 |
| | | |
+---------+---------+---------+
@@ -1008,9 +1008,10 @@ Abstract
1 bit: ISEMPTY, set to 1 if the meta-block is empty, this
field is only present if ISLAST bit is set, since
only the last meta-block can be empty
2 bits: MNIBBLES, (# of nibbles to represent the length) - 4
2 bits: MNIBBLES - 4, where MNIBBLES is # of nibbles to represent
the length
(MNIBBLES + 4) x 4 bits: MLEN - 1, where MLEN is the length
MNIBBLES x 4 bits: MLEN - 1, where MLEN is the length
of the meta-block in the input data in bytes
1 bit: ISUNCOMPRESSED, if set to 1, any bits of input up to