Optimize bg4 prediction #308
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Method gives a 2x speedup. |
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This PR optimizes the bg4 prediction used in the compression scheme analysis by bypassing the per-byte popcnt call, which can be quite slow. This was shown to be a bottleneck; this PR speeds this operation up.
On Arm/neon, this uses an intrinsic vector popcnt instruction, and on intel it uses a bit twiddling method to calculate the per-byte popcount on u128s that is much more efficient than subsequent popcnt calls.