* better froxel records compression
We used to compress froxel records by reusing the
previous record on the left if it was identical,
now we additionally check the record above if
that fails.
In practice this saves 10% to 30% space in the
froxel record buffer, which is a scarce resource
for us.
e.g. if a light occupied 3x3 froxels in a given
z-slice, without compression 9 records would be
used, with left-only compression, only 3,
and with left+above compression, only 1.
* use size_t for in and out parameters
this helps the compiler in many places, not
having to cast from 64 to 32 bits.
* implement bitset’s any() and all() operations with NEON
* empty froxels are a common case, handle it first
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