VTD-XML Home
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A Quick
Overview on Virtual Token Descriptor
- It is a binary format
specification, not an API specification
- A VTD record is a
primitive data type (integer multiple of 32 bits) that encodes the
following parameters of a token in an XML file:
- Starting offset
- Length
- Nesting depth
- Token type
- VTD requires that
XML document be maintained intact in memory.
- Our current VTD
record layout further specifies the following:
- Use 64
bits as the primitive type (b63~b0)
- Big endian
- Starting offset:
30 bits (b29 ~ b0) maximum value is 2^30 -1 = 1G
-1
- Length: 20
bits (b51 ~ b32) maximum value is 2^20-1 = 1M -1
- For some token type
- Prefix length:
9 bits (b51~
b43) max
value 511
- Q-name length:
11 bits (b42 ~ b 32) max value 1023
- Depth: 8
bits (b59~b52) max value is 2^8-1 = 255
- Token type:
4 bits (b63~b60)
- Reserved bit:
2 bits (b31: b30)
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