See more on Chunks in general.
This is a data used to seed a dictionary-based compression algorithm. A dictionary-based compression engine sucb as Deflation may be pre-loaded with data that is representative of the content being compressed. If multiple files refer to the same dictionary, you save space. Using a pre-defined dictionary really saves space, since it is not included explicitly in the archive at all.
Flag | usage |
---|---|
a (correlated) | Cleared. |
b (subtype) | Set. |
r (range of instances) | all used in the general manner. |
p (multi-part) & c | |
y (payload specification) | |
i (instance sizes) | Set when r is set, Clear otherwise. |
n (pointer) | Cleared. If set, see the DICT-n or DICT-nd definitions instead. |
d (redundant) |
Although the y (payload specification) is allowed, it may not refer to itself!
Subtype is set to 65 (hex 41).
The Instance Number is matched against a parameter in a COMP chunk that is documented to refer to a DICT instance.
Instance numbers from hex 40 through hex FFF (64 through 4095) are reserved. An archive shall not contain instances in this range.
Instance | Meaning |
---|---|
64 | C/C++ Source Code |
65 | Perl Source Code |
∴To be determined |
The binary definition of these pre-defined dictionaries are found in the pre-defined chunk files.
The Payload contains
A part number, as with DATA.
A URL.
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