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41 lines
1.5 KiB
Markdown
41 lines
1.5 KiB
Markdown
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# Add-on Block
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Fixed storage which stores an immutable binary-search tree of items.
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Each item consists of a pair of pointers to binary data of arbitrary length.
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These two pointers are interpreted as a `key` and a `value`.
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Since items contain only pointers, multiple instances of data are stored just once.
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Block contains 3 logical parts:
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a) header (256 bytes)
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b) binary-search tree (variable size)
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c) item data (variable size)
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## Header
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| offset | length | name | description |
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|-------:|---------:|--------------|--------------|
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| 0x0000 | 4 | magic | magic `TRAB` |
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| 0x0004 | 64 | sig | signature of the whole blob (except magic and sig) |
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| 0x0044 | 4 | tree_count | number of elements in the tree |
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| 0x0048 | 4 | items_size | length of the item section |
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| 0x004A | 182 | reserved | - |
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## Binary-Search Tree
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Each node of the tree has the following structure:
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| offset | length | name | description |
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|-------:|---------:|--------------|--------------|
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| ... | 2 | key_offset | key offset (divided by 4) |
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| ... | 2 | value_offset | value offset (divided by 4) |
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# Item Data
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Each item has the following structure:
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| offset | length | name | description |
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|-------:|---------:|--------------|--------------|
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| ... | 2 | item_len | item (key or value) length |
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| ... | 2 | item_flags | item (key or value) flags |
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| ... | item_len | item_data | item (key or value) data (padded to multiple of 4) |
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