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Edits as per comments, and change wildcard 'X' to '?'

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Sean Purcell 2017-01-26 16:58:25 -08:00
parent 81c9670226
commit d86153d903
1 changed files with 9 additions and 5 deletions
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doc/zstd_compression_format.md
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@ -116,7 +116,7 @@ Skippable frames defined in this specification are compatible with [LZ4] ones.
__`Magic_Number`__ __`Magic_Number`__
4 Bytes, little-endian format. 4 Bytes, little-endian format.
Value : 0x184D2A5X, which means any value from 0x184D2A50 to 0x184D2A5F. Value : 0x184D2A5?, which means any value from 0x184D2A50 to 0x184D2A5F.
All 16 values are valid to identify a skippable frame. All 16 values are valid to identify a skippable frame.
__`Frame_Size`__ __`Frame_Size`__
@ -477,13 +477,16 @@ For values spanning several bytes, convention is little-endian.
__`Size_Format` for `Raw_Literals_Block` and `RLE_Literals_Block`__ : __`Size_Format` for `Raw_Literals_Block` and `RLE_Literals_Block`__ :
- Value X0 : `Size_Format` uses 1 bit, `Regenerated_Size` uses 5 bits (0-31). - Value ?0 : `Size_Format` uses 1 bit.
`Regenerated_Size` uses 5 bits (0-31).
`Literals_Section_Header` has 1 byte. `Literals_Section_Header` has 1 byte.
`Regenerated_Size = Header[0]>>3` `Regenerated_Size = Header[0]>>3`
- Value 01 : `Regenerated_Size` uses 12 bits (0-4095). - Value 01 : `Size_Format` uses 2 bits.
`Regenerated_Size` uses 12 bits (0-4095).
`Literals_Section_Header` has 2 bytes. `Literals_Section_Header` has 2 bytes.
`Regenerated_Size = (Header[0]>>4) + (Header[1]<<4)` `Regenerated_Size = (Header[0]>>4) + (Header[1]<<4)`
- Value 11 : `Regenerated_Size` uses 20 bits (0-1048575). - Value 11 : `Size_Format` uses 2 bits.
`Regenerated_Size` uses 20 bits (0-1048575).
`Literals_Section_Header` has 3 bytes. `Literals_Section_Header` has 3 bytes.
`Regenerated_Size = (Header[0]>>4) + (Header[1]<<4) + (Header[2]<<12)` `Regenerated_Size = (Header[0]>>4) + (Header[1]<<4) + (Header[2]<<12)`
@ -580,7 +583,8 @@ which describes how to decode the list of weights.
- if `headerByte` >= 128 : this is a direct representation, - if `headerByte` >= 128 : this is a direct representation,
where each `Weight` is written directly as a 4 bits field (0-15). where each `Weight` is written directly as a 4 bits field (0-15).
They are encoded forward, 2 weights to a byte with the first weight taking They are encoded forward, 2 weights to a byte with the first weight taking
the top four bits and the second taking the bottom four (e.g. the top four bits and the second taking the bottom four (e.g. the following
operations could be used to read the weights:
`Weight[0] = (Byte[0] >> 4), Weight[1] = (Byte[0] & 0xf)`, etc.). `Weight[0] = (Byte[0] >> 4), Weight[1] = (Byte[0] & 0xf)`, etc.).
The full representation occupies `((Number_of_Symbols+1)/2)` bytes, The full representation occupies `((Number_of_Symbols+1)/2)` bytes,
meaning it uses a last full byte even if `Number_of_Symbols` is odd. meaning it uses a last full byte even if `Number_of_Symbols` is odd.