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Comment by QuickToBan | Hacker News Reader

Posits seem great, but LLNL seems to favor ZFP[1], not posits.[2] Maybe new chips should then implement both posits and ZFP.

[1] https://github.com/LLNL/zfp

[2] https://helper.ipam.ucla.edu/publications/bdcws2/bdcws2_1504...

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Unrelated as far as I can tell. Posits are an alternative floating point format, not an array compression algorithm. The “compression” benefits from being able to use posit floats instead of ieee754 doubles, because of the better precision.

Posits also take less space for the same total accuracy, they use less space on disk, ram and less memory bandwidth.

It occurs to me that maybe you are referring to unums? The "unum" format discussed in "End of Error" is variable sized. However they since dropped that design and switched to fixed-sized number formats (16-, 32-, or 64-bit) with adjustable division between exponent and fraction bits, the "posit."

So "posit" numbers get you the ability to tradeoff precision and range, but they're not anymore highly compressed than regular old IEEE floats. Unless, as Gustafson argues, you didn't need a double in the first place and the added features of posits let you switch to a float.

Not really... there is a standard 32-bit and 64-bit representation of posits. They use the same memory as a float or a double, just with better accuracy and other desirable properties. You only reduce storage space if you switch from “double” to “float”, which you can only do if you didn’t need most of the precision of a double in the first place. They’re not THAT much better.

Zfp is lossy compression just FYI. Fpzip (an earlier invention by Lindstrom et al) has a lossless mode. They really push zfp more though as it has nice features like random access decoding and (except on my data) higher compression ratios.

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