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.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 valueXtimes - 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:
| Dec | Enc |
|---|---|
| 1 | 1 |
| 1 | blank = d0 = 1+0 = 1 |
| 1 | n2 = previous value twice = d0 = 1+0 = 1 |
| 1 | " |
| 2 | 1 = d1 = 1+1 = 2 |
| 3 | n2 = previous value twice = d1 = 2+1 = 3 |
| 4 | " = d1 = 3+1 = 4 |
| 4 | blank = d0 = 4+0 = 4 |
| 4 | blank = d0 = 4+0 = 4 |
| 3 | -1 = d-1 = 4-1 = 3 |
| 2 | n3 = previous value thrice = d-1 = 3-1 = 2 |
| 1 | " = d-1 = 2-1 = 1 |
| 0 | " = d-1 = 1-1 = 0 |
| 0 | blank = d0 = 0+0 = 0 |
| 0 | blank = d0 = 0+0 = 0 |