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The output buffer may alias decoder members of the same type, forcing repeated reloads after stores. Keep the frame and running value in locals, write back once, and preserve unsigned wrapping during reconstruction.
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Adjacent equal-width miniblocks form one packed stream. Decode each run with one unpack call, bounded by the current block and output request; retain the zero-width path and cover width changes, partial reads, block boundaries, and both integer widths.
Replace the dependent scalar additions with an inclusive SIMD scan for batches of at least four lanes. Retain scalar handling for narrower batches and tails, preserve unsigned wrapping, and cover every residual width, both block sizes, and wrapped totals.
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Rationale for this change
Prefix sum: a chain of dependent additions. A log-step inclusive scan computes it a register at a
time, in log2(lanes) shifted additions. Adding the frame of reference before the scan turns
its running multiple into a term the scan produces, rather than a multiply per lane.
What changes are included in this PR?
I replaced the sequential addition loop with a vectorized prefix sum (scan) to speed up decoding.
Are these changes tested?
Yes. I added a new typed test that explicitly forces the decoder through the vector loop, the scalar remainder loop, and the hand-off between them to ensure totals and wrapping behave correctly.
Benchmark
Same setup as #51250.
NarrowSortedis added by this PR and holds non-decreasing values,the shape DELTA_BINARY_PACKED is usually chosen for.
Decode_Int32_NarrowSortedDecode_Int32_NarrowDecode_Int32_WideDecode_Int64_NarrowSortedDecode_Int64_NarrowDecode_Int64_WideDecode_Int32_FixedDecode_Int64_FixedAre there any user-facing changes?
No. No API change, no format change, and decoded values are identical.