Small update to brotli specification.
Clarify how to recover from error conditions caused by overflowing
block types and symbol values.
diff --git a/brotli/brotlispec.txt b/brotli/brotlispec.txt
index 9bad7ba..765abfb 100644
--- a/brotli/brotlispec.txt
+++ b/brotli/brotlispec.txt
@@ -432,7 +432,9 @@
The value of ALPHABET_BITS depends on the alphabet of the Huffman
code: it is the smallest number of bits that can represent all
symbols in the alphabet. E.g. for the alphabet of literal bytes,
- ALPHABET_BITS is 8.
+ ALPHABET_BITS is 8. The value of each of the NSYM symbols above is
+ the value of the ALPHABETS_BITS width machine integer representing
+ the symbol modulo the alphabet size of the Huffman code.
The (non-zero) code lengths of the symbols can be reconstructed as
follows:
@@ -714,9 +716,11 @@
alphabet. A block type code 0 means that the block type is the same
as the type of the second last block from the same block category,
while a block type code 1 means that the block type equals the last
- block type plus one. Block type codes 2 - 257 represent block types
- 0 - 255. The second last and last block types are initialized with 0
- and 1, respectively, at the beginning of each meta-block.
+ block type plus one. If the last block type is the maximal possible,
+ then a block type code 1 means block type 0. Block type codes 2 - 257
+ represent block types 0 - 255. The second last and last block types
+ are initialized with 0 and 1, respectively, at the beginning of each
+ meta-block.
The first block type of each block category must be 0 and the block
type of the first block switch command is therefore not encoded in
