zp-extern-struct-padding — extern-struct-padding

ClaimCopy Anchor Link

Walk hot u64 fields of padded vs alignment-sorted extern structs under Zig 0.17.0 -Ofast on this Linux machine shows a clear before/after wall-clock gap.

How measuredCopy Anchor Link

• Harness: packages/zperf/examples/bench/evidence_fill.zig (rule zp-extern-struct-padding cases)
• Build: zig build-exe -Ofast · optimize_mode=fast
• Timing: Io.Clock awake; warm=2; median of 9 rounds
• before: extern_padded_walk
• after: extern_packed_walk
• ops=2000000
• Raw: zp-extern-struct-padding.jsonl

Runtime (this evidence file)Copy Anchor Link

Lint mappingCopy Anchor Link

zperf-lint zp-extern-struct-padding / extern-struct-padding. Default severity in rules.zig is off (the CLI does not report the rule); see evidence-policy for keep/escalate. Evidence exists and agrees directionally.

VerdictCopy Anchor Link

Agree ~1.21× bandwidth for this shape (24B→16B class); modest.

LimitsCopy Anchor Link

ABI-locked layouts must ignore; only when all field sizes known.