XDelta Compression Format

The XINA Delta (xd) compression format is a simple, high performance format for compression and decompression of a list of numeric values into a string. The compression is most efficient for data sets with frequently repeated values, or predictable value iterations.

The format consists of a few main features:

• a comma separated list of values
• blank values indicating either repeating the previous value, or a static value
• "nX" indicates repeating the previous value X times
• each point is a delta of the previous point (which can be applied recursively)
• transformation of values (typically just to reduce their size, since the format is plain-text)

The configuration of the encoding of a particular string is denoted by a comma delimited set of steps. These are:

• b<number> - blanks are provided static value
• br - blanks repeat previous value
• d - single iteration delta
• dd - double iteration delta
• +<number> - add static value
• -<number> - subtract static value
• *<number> - multiply by static value
• /<number> - divide by static value

This is followed by a colon, and the encoded data.

For example, given the array of numbers:

1, 1, 1, 1, 2, 3, 4, 4, 4, 3, 2, 1, 0, 0, 0

One possible encoding would be:

"d,b0:1,,n2,1,n2,,,-1,n3,,"

Breaking this down: