zp-shift-on-read — shift-on-read
Claim
copyForwards compact after prefix consume vs cursor head under Zig 0.17.0 -Ofast on this Linux machine shows a clear before/after wall-clock gap.
How measured
- Harness:
packages/zperf/examples/bench/evidence_fill.zig(rulezp-shift-on-readcases) - Build:
zig build-exe -Ofast· optimize_mode=fast - Timing:
Io.Clockawake; warm=2; median of 9 rounds - before:
copy_forwards_consume - after:
cursor_head - ops=20000
- Raw:
zp-shift-on-read.jsonl
Runtime (this evidence file)
| Field | Value |
|---|---|
| When | 2026-10-21 Asia/Shanghai (JSONL ts is UTC) |
| Zig | 0.17.0 · fast |
| Median before | ~0.2825 ms |
| Median after | ~0.01686 ms |
| ratio before/after | ~16.8× |
Lint mapping
zperf-lint zp-shift-on-read / shift-on-read. Default severity in rules.zig is warning; see evidence-policy for keep/escalate. Evidence exists and agrees directionally.
Verdict
Agree ~16.8× when repeatedly sliding remaining bytes.
Limits
Amortize with read cursor; compact only when needed.