Remove the per-item heap allocation from Accumulator::add - #12
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`add` is called once per item while sealing a storage, so building a
100,000-item client store performed 100,000 heap allocations. Each one was
a 32-byte `Vec` holding four `u64` lanes, copied over `self.buf` and freed
immediately.
Write each lane straight back into `self.buf` and track the carry with
`overflowing_add` instead. The arithmetic is the same four-lane
little-endian addition; only the scratch buffer and the `Wrapping`
comparisons around it are gone.
Measured on a 100,000-item client store reconciling against a 110,000-item
relay, best of 25 runs:
client build and reconcile 2345 us -> 650 us
full exchange 4617 us -> 846 us
allocations 107,033 -> 620
Peak memory is unchanged: the removed allocations were short-lived and
never coexisted.
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addis called once per item while sealing a storage, so building a 100,000-item client store performed 100,000 heap allocations. Each one was a 32-byteVecholding fouru64lanes, copied overself.bufand freed immediately.Write each lane straight back into
self.bufand track the carry withoverflowing_addinstead. The arithmetic is the same four-lane little-endian addition; only the scratch buffer and theWrappingcomparisons around it are gone.Measured on a 100,000-item client store reconciling against a 110,000-item relay, best of 25 runs:
make precommitbefore committing