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Fix negative score order (backward incompatible!) #35

Merged

hltbra merged 1 commit into master from bugfix/reorder-negative-zset-score

Jun 27, 2019

Commits on Jun 26, 2019

Fix negative score order (backward incompatible!)

Before this commit, sorted set negative scores were stored after
all positive scores because of their binary representation.
For example:
    >>> struct.pack('>d', -1)
    b'\xbf\xf0\x00\x00\x00\x00\x00\x00'
    >>> struct.pack('>d', +1)
    b'?\xf0\x00\x00\x00\x00\x00\x00'
    >>> struct.pack('>d', -1) < struct.pack('>d', +1)
    False

This commit introduces the FloatCodec class to encode/decode floats into bytes and vice-versa, preserving their numerical order.
For example, the following list is encoded to bytes while keeping and preserves its numerical order:
    >>> floats = [1.5, -2.5, 3.2, 2.0]
    >>> sorted(floats, key=FloatCodec().encode)
    [-2.5, 1.5, 2.0, 3.2]

References:
* https://en.wikipedia.org/wiki/Floating-point_arithmetic#IEEE_754_design_rationale
* https://stackoverflow.com/a/43305015/565999
* https://stackoverflow.com/a/12933766/565999
* https://ananthakumaran.in/2018/08/17/order-preserving-serialization.html
* https://ananthakumaran.in/2018/08/17/order-preserving-serialization.html#float

WARNING: This is a backward incompatible change and requires a major release!

hltbra committed Jun 26, 2019