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  • SZ 0.5.8 Refine the leading-zero granularity (change it from byte to bits based on the distribution). For example, in SZ0.5.7, the leading-zero is always in bytes, 0, 1, 2, or 3. In SZ0.5.8, the leading-zero part could be xxxx xxxx xx xx xx xx xxxx xxxx (where each x means a bit in the leading-zero part)
  • SZ 0.5.9 optimize the offset by using simple right-shifting method. Experiments show that this cannot improve compression ratio actually, because simple right-shifting actually make each data be multiplied by 2^{-k}, where k is # right-shifting bits. The pros is to save bits because of more leading-zero bytes, but the cons is much more required bits to save. See SZ 0.5.10 for the better solution on this issue!
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  • SZ 0.5.10 optimizes the offset by using the optimized formula of computing the median_value based on optimized right-shifting method. Anyway, this version improves compression ratio a lot for hard-to-compress datasets. (Hard-to-compress datasets refer to the cases whose compression ratios are usually very limited)
  • SZ 0.5.11 improved SZ 0.5.10 on the level of guaranteeing user-specified error bounds. In a very few cases, SZ 0.5.10 cannot guarantee the error-bounds to a certain user-specified level. For example, when absolute error bound = 1E-6, the maximum decompression error may be 0.01(>>1E-6) because of the huge value range even in the optimized segments such that the normalized data cannot reach the required precision even storing all of the 64 or 32 mantissa bits. SZ 0.5.11 fixed the problem well, with compression ratio degraded by less than 1% in that case. 
  • SZ 0.5.12 allows users to set "offset" parameter in the configuration file sz.config. The value of offset is an integer in [1,7]. Generally, we recommend offset=2 or 3, while we also find that some other settings (such as offset=7) may lead to better compression ratios in some cases. How to automize/optimize the selection of offset value would be the future work. In addition, the compression speed is improved, by replacing java List by array implementation in the code.
  • SZ 0.5.13 improves compression performance, by replacing the implementation with classes by that of primitive data types.
  • SZ 0.5.14 fixed a design bug, which improves the compression ratio further.


  • 14 (up-to-date versoin)

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