Distillation

Date: July 30, 2026

• 🔴 (21:22) User stated their orders/data conventions as an aside with no action requested: read returns buffer "always exactly len bytes", diff/extra decompression readers "always cancelled before", base "never sits fully in" memory, reads "never crosses EOF", fd "never fully opened */". These are durable properties of the binpatch library, not to be treated as throwaway context.
• 🔴 (21:22) User asked to run real benchmarks for binpatch library's SWAR (SIMD-within-a-register) optimizations on /home/byk/Code/binpatch, specifically src/bspatch.ts diff-add loop. Three implementations to compare: (1) naive byte loop for (let i = 0; i < n; i++) dest[i] += diff[i], (2) Uint32Array SWAR (4x4-byte) using ((a & mask) + (b & mask)) ^ ((a ^ b) & sign) with mask=0x7f7f7f7f, sign=0x80808080, (3) BigUint64Array (8-byte) using same XOR trick — expected to be WRONG due to carry propagation across byte lanes.
• 🔴 (21:22) User stated benchmark scenario requirements: 100 MB dest buffer, mostly-zero diff blocks (zeros mixed with random bytes weighted heavily toward zero — "narrow-gap" diff, dominant pattern in real bsdiff patches). Run each implementation 5 times, take median.
• 🔴 (21:22) User stated reporting requirements: (a) machine specs via uname -a and lscpu, (b) node --version, (c) median time for each implementation in ms, (d) caveats if BigUint64Array output diverges (don't report timings for incorrect result).
• 🟡 (21:22) User specified write benchmark script to /tmp/opencode/swar-bench.mjs, isolate diff-add loop only (not full bsdiff pipeline).
• 🟡 (21:22) binpatch repo structure: /home/byk/Code/binpatch contains src/, test/, action/, website/, dist/, .github/, node_modules/, package.json, tsconfig.json, tsup.config.ts, vitest.config.ts, AGENTS.md, CHANGELOG.md, README.md, LICENSE, .craft.yml, .gitignore, .lore.md, logo-brief.md. test/ contains bspatch.test.ts, discover.test.ts, sources.test.ts. No existing benchmark files.
• 🟡 (21:23) Machine specs: Linux labs 6.8.0-117-generic #117-Ubuntu SMP PREEMPT_DYNAMIC x86_64. CPU: Intel(R) Core(TM) i5-6500T @ 2.50GHz (max 3100 MHz, min 800 MHz), family 6, model 94, stepping 3. 4 CPUs (1 socket, 4 cores, 1 thread/core — no SMT). L1d 128 KiB, L1i 128 KiB, L2 1 MiB, L3 6 MiB. Flags include sse2, ssse3, sse4_1, sse4_2, avx, avx2, bmi1, bmi2, aes, fma, popcnt. No AVX-512. NUMA 1 node (0-3).
• 🟡 (21:23) Node.js version: v24.16.0
• 🟡 (21:23) User lore reference invoked: "binpatch benchmark: multi-pair median over single-pair (decision)" — applies multi-pair median methodology to SWAR benchmark.
• 🟡 (21:23) Benchmark script written to /tmp/opencode/swar-bench.mjs (file created successfully).