Yann's Blog - Software and hardware

So the magic 0x2A encoding in the cache files had me stumped for several days. I could see some of the data, but the packing was… odd (and no real price ever materialized out of it, turns out its a 64 bit integer, with lots of 0s ). The real problem was the zeros, or the lack of them. Turns out the packing algorithm appears to be optimized to simply not encode zero bytes, slightly reducing space. I believe that the first byte (and every “code” byte thereafter), which is split into two nibbles for this algorithm, contains a count of zeros and not zeros (bytes it simply copies to the output stream). This appears to be exclusive – either 0 is inserted or bytes are copied (per nibble), but not both.

I can’t fully verify this as I don’t have any “unpacked” in the same format, but by unpacking I can now locate more relevant data fields. Yay!