Rewrite varlen 32-byte block encoder with copy_nonoverlapping#7999
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The byte-at-a-time XOR loop is per-byte branch-heavy: 32 conditional writes per block on each path, even for the ascending (no-XOR) case where the body is exactly a `memcpy(32) + stamp(1)`. Rewrite `encode_varlen_value` with two distinct fast paths: - Ascending: `copy_nonoverlapping(src, dst, 32)` + a single 0xFF stamp. The compiler folds the loop into a SIMD memcpy. - Descending: a `xor_copy_block` helper that XOR-copies 32 bytes via four u64 reads/writes; LLVM lowers it to SIMD on x86. The partial-block tail uses `write_bytes` for the zero-padding instead of a per-byte loop. utf8 throughput: ~0.92 GB/s → ~1.39 GB/s. struct_mixed: +35%. Signed-off-by: Claude <noreply@anthropic.com>
This was referenced May 18, 2026
This was referenced May 18, 2026
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Part 14 of 25 in the stacked PR series adding
vortex-row.This PR contains exactly one commit; review just that diff in isolation.
What this commit does
The byte-at-a-time XOR loop is per-byte branch-heavy: 32 conditional writes per block on each path, even for the ascending (no-XOR) case where the body is exactly a
memcpy(32) + stamp(1).Rewrites
encode_varlen_valuewith two distinct fast paths:copy_nonoverlapping(src, dst, 32)+ a single 0xFF stamp. The compiler folds the loop into a SIMD memcpy.xor_copy_blockhelper that XOR-copies 32 bytes via four u64 reads/writes; LLVM lowers it to SIMD on x86.The partial-block tail uses
write_bytesfor the zero-padding instead of a per-byte loop. utf8 throughput: ~0.92 GB/s → ~1.39 GB/s. struct_mixed: +35%.Stack
claude/row-c01-crate-scaffoldingclaude/row-c02-sortfield-optionsclaude/row-c03-codec-fixed-widthclaude/row-c04-codec-varlenclaude/row-c05-codec-nestedclaude/row-c06-rowsize-scalarfnclaude/row-c07-rowencode-scalarfnclaude/row-c08-convert-columns-tests-benchclaude/row-c09-skip-listview-validationclaude/row-c10-validity-fast-pathclaude/row-c11-skip-zero-initclaude/row-c12-vectorize-pure-fixed-offsetsclaude/row-c13-vectorize-mixed-offsetsclaude/row-c14-varlen-block-copy-nonoverlappingclaude/row-c15-walk-varbinview-directlyclaude/row-c16-arith-write-fast-pathclaude/row-c17-specialize-constant-arithclaude/row-c18-kernel-dispatch-helpersclaude/row-c19-inventory-registryclaude/row-c20-constant-kernelclaude/row-c21-dict-kernelclaude/row-c22-patched-kernelclaude/row-c23-runend-kernelclaude/row-c24-bitpacked-kernelclaude/row-pr3-kernelsBase of this PR: #7998 (
claude/row-c13-vectorize-mixed-offsets)Next in stack: #8000 (
claude/row-c15-walk-varbinview-directly)Combined context
For the full design + rationale, see PR #7985 (top of stack).