diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/draft-alakuijala-brotli-07.nroff | 18 |
1 files changed, 10 insertions, 8 deletions
diff --git a/docs/draft-alakuijala-brotli-07.nroff b/docs/draft-alakuijala-brotli-07.nroff index 0954673..bbde0f1 100644 --- a/docs/draft-alakuijala-brotli-07.nroff +++ b/docs/draft-alakuijala-brotli-07.nroff @@ -617,8 +617,9 @@ for the various prefix codes and the sections where they are defined. The first two bits of the compressed representation of each prefix code distinguishes between simple and complex prefix -codes. If this value is 1, then a simple prefix code follows. -Otherwise the value indicates the number of leading zeros. +codes. If this value is 1, then a simple prefix code follows +as described in this section. Otherwise, a complex prefix code +follows as described in Section 3.5. A simple prefix code can have only up to four symbols with non-zero code length. The format of the simple prefix code is as @@ -637,9 +638,10 @@ The value of ALPHABET_BITS depends on the alphabet of the prefix 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. The value of each of the NSYM symbols above is -the value of the ALPHABETS_BITS width integer value. (If the integer -value is greater than or equal to the alphabet size, then the stream -should be rejected as invalid.) +the value of the ALPHABETS_BITS width integer value. If the integer +value is greater than or equal to the alphabet size, or the value +is identical to a previous value, then the stream should be rejected +as invalid. Note that the NSYM symbols may not be presented in sorted order. Prefix codes of the same bit length must be assigned to the symbols in sorted order. @@ -757,7 +759,7 @@ We can now define the format of the complex prefix code as follows: If there are at least two non-zero code lengths, any trailing zero code lengths are omitted, i.e. the last code length in the sequence must be non-zero. In this - case the sum of (32 >> code length) over all the non-zero + case, the sum of (32 >> code length) over all the non-zero code lengths must equal to 32. If the lengths have been read for the entire code length @@ -775,8 +777,8 @@ We can now define the format of the complex prefix code as follows: length is taken to be 8 before any code length code lengths are read. - Sequence of code lengths symbols, encoded using the code - length prefix code. Any trailing 0 or 17 must be + Sequence of at most alphabet size code lengths symbols, encoded + using the code length prefix code. Any trailing 0 or 17 must be omitted, i.e. the last encoded code length symbol must be between 1 and 16. The sum of (32768 >> code length) over all the non-zero code lengths in the alphabet, including |