172 lines
4.9 KiB
Markdown
172 lines
4.9 KiB
Markdown
![]() |
# Quick notes about binary CMap format (bcmap)
|
|||
|
|
|||
|
The format is designed to package some information from the CMap files located at external/cmap. Please notice for size optimization reasons, the original information blocks can be changed (split or joined) and items in the blocks can be swaped.
|
|||
|
|
|||
|
The data stored in binary format in network byte order (big-endian).
|
|||
|
|
|||
|
# Data primitives
|
|||
|
|
|||
|
The following primitives used during encoding of the file:
|
|||
|
- byte (B) – a byte, bits are numbered from 0 (less significant) to 7 (most significant)
|
|||
|
- bytes block (B[n]) – a sequence of n bytes
|
|||
|
- unsigned number (UN) – the number is encoded as sequence of bytes, bit 7 is flag to continue decoding the byte, bits 6-0 store number information, e.g. bytes 0x818407 will represent 16903 (0x4207). Limited to the 32 bit.
|
|||
|
- signed number (SN) – the number is encoded as sequence of bytes, as UN, however shall be transformed before encoding: if n < 0, the n shall be encoded as (-2*n-1) using UN encoding, other n shall be encoded as (2*n) using UN encoding. So the lowest bit of the number indicates the sign of the initial number
|
|||
|
- unsigned fixed number (UB[n]) – similar to the UN, but it represents an unsigned number that is stored in B[n]
|
|||
|
- signed fixed number (SB[n]) – similar to the SN, but it represents a signed number that is stored in B[n]
|
|||
|
- string (S) – the string is encoded as sequence of bytes. First comes length is characters encoded as UN, when UTF16 characters encoded as UN.
|
|||
|
|
|||
|
# File structure
|
|||
|
|
|||
|
The first byte is a header:
|
|||
|
- bits 2-1 – indicate a CMapType. Valid values are 1 and 2
|
|||
|
- bit 0 – indicate WMode. Valid values are 0 and 1.
|
|||
|
|
|||
|
Then records follow. The records starts from the record header encoded as B, where bits 7-5 indicate record type (see description of other bits below):
|
|||
|
- 0 – codespacerange
|
|||
|
- 1 – notdefrange
|
|||
|
- 2 – cidchar
|
|||
|
- 3 – cidrange
|
|||
|
- 4 – bfchar
|
|||
|
- 5 – bfrange
|
|||
|
- 6 – reserved
|
|||
|
- 7 – metadata
|
|||
|
|
|||
|
## Metadata record
|
|||
|
|
|||
|
The metadata record header bit 4-0 contain id of the metadata:
|
|||
|
- 0 – comment, body of the record is encoded comment string (S)
|
|||
|
- 1 – UseCMap, body of the record is usecmap id string (S)
|
|||
|
|
|||
|
## Data records
|
|||
|
|
|||
|
The records that have types 0 – 5, have the following fields in the header:
|
|||
|
- bit 4 – indicate the char or start/end entries are stored in a sequence in this block
|
|||
|
- bits 3-0 – contain length of the data size minus 1 in this block (dataSize)
|
|||
|
|
|||
|
The amount of entries encoded as UN follows the header. The items records follow (see below).
|
|||
|
|
|||
|
|
|||
|
### codespacerange (0)
|
|||
|
|
|||
|
Represents the following CMap block:
|
|||
|
|
|||
|
n begincodespacerange
|
|||
|
<start> <end>
|
|||
|
endcodespacerange
|
|||
|
|
|||
|
First record format is:
|
|||
|
|
|||
|
- start as B[dataSize]
|
|||
|
- endDelta as UB[dataSize], end is calculated as (start + endDelta)
|
|||
|
|
|||
|
Next record format is:
|
|||
|
|
|||
|
- startDelta as UB[dataSize], start = end + startDelta
|
|||
|
- endDelta as UB[dataSize], end = start + endDelta
|
|||
|
|
|||
|
|
|||
|
### notdefrange (1)
|
|||
|
|
|||
|
Represents the following CMap block:
|
|||
|
|
|||
|
n beginnotdefrange
|
|||
|
<start> <end> code
|
|||
|
endnotdefrange
|
|||
|
|
|||
|
First record format is:
|
|||
|
|
|||
|
- start as B[dataSize]
|
|||
|
- endDelta as UB[dataSize], end is calculated as (start + endDelta)
|
|||
|
- code as UN
|
|||
|
|
|||
|
Next record format is:
|
|||
|
|
|||
|
- startDelta as UB[dataSize], start = end + startDelta
|
|||
|
- endDelta as UB[dataSize], end = start + endDelta
|
|||
|
- code as UN
|
|||
|
|
|||
|
|
|||
|
### cidchar (2)
|
|||
|
|
|||
|
Represents the following CMap block:
|
|||
|
|
|||
|
n begincidchar
|
|||
|
<char> code
|
|||
|
endcidchar
|
|||
|
|
|||
|
First record format is:
|
|||
|
|
|||
|
- char as B[dataSize]
|
|||
|
- code as UN
|
|||
|
|
|||
|
Next record format is:
|
|||
|
|
|||
|
- if sequence = 0, charDelta as UB[dataSize], char = char + charDelta + 1
|
|||
|
- if sequence = 1, char = char + 1
|
|||
|
- codeDelta as SN, code = code + codeDelta
|
|||
|
|
|||
|
|
|||
|
### cidrange (3)
|
|||
|
|
|||
|
Represents the following CMap block:
|
|||
|
|
|||
|
n begincidrange
|
|||
|
<start> <end> code
|
|||
|
endcidrange
|
|||
|
|
|||
|
First record format is:
|
|||
|
|
|||
|
- start as B[dataSize]
|
|||
|
- endDelta as UN[dataSize], end is calculated as (start + endDelta)
|
|||
|
- code as UN
|
|||
|
|
|||
|
Next record format is:
|
|||
|
|
|||
|
- if sequence = 0, startDelta as UB[dataSize], start = end + startDelta + 1
|
|||
|
- if sequence = 1, start = end + 1
|
|||
|
- endDelta as UN[dataSize], end = start + endDelta
|
|||
|
- code as UN
|
|||
|
|
|||
|
|
|||
|
### bfchar (4)
|
|||
|
|
|||
|
Represents the following CMap block:
|
|||
|
|
|||
|
n beginbfchar
|
|||
|
<char> <code>
|
|||
|
endbfchar
|
|||
|
|
|||
|
First record format is:
|
|||
|
|
|||
|
- char as B[ucs2Size], where ucs2Size = 2 (here and below)
|
|||
|
- code as B[dataSize]
|
|||
|
|
|||
|
Next record format is:
|
|||
|
|
|||
|
- if sequence = 0, charDelta as UN[ucs2Size], char = charDelta + charDelta + 1
|
|||
|
- if sequence = 1, char = char + 1
|
|||
|
- codeDelta as SB[dataSize], code = code + codeDelta
|
|||
|
|
|||
|
|
|||
|
### bfrange (5)
|
|||
|
|
|||
|
Represents the following CMap block:
|
|||
|
|
|||
|
n beginbfrange
|
|||
|
<start> <end> <code>
|
|||
|
endbfrange
|
|||
|
|
|||
|
First record format is:
|
|||
|
|
|||
|
- start as B[ucs2Size]
|
|||
|
- endDelta as UB[ucs2Size], end is calculated as (start + endDelta)
|
|||
|
- code as B[dataSize]
|
|||
|
|
|||
|
Next record format is:
|
|||
|
|
|||
|
- if sequence = 0, startDelta as UB[ucs2Size], start = end + startDelta + 1
|
|||
|
- if sequence = 1, start = end + 1
|
|||
|
- endDelta as UB[ucs2Size], end = start + endDelta
|
|||
|
- code as B[dataSize]
|
|||
|
|