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String-scaling gate misses quadratic len-of scans because length is measured outside the timer

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
68/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
c, shell
Domain
performance, testing-qa

Research direction

Start with tests/test_string_scaling.sh and inspect the builtin_len change described in the issue. Reproduce the current and mutant timings with the supplied commands, then add separately timed len-of-in-loop coverage with a cache-removal control, or narrow the gate's stated coverage. Preserve the existing indexing coverage and verify the gate distinguishes both regressions.

Written by the indexing model from the issue text.

Description

area:gates found-by:critic kind:gate-defect

The string-scaling gate enrolled by PR #1187 claims len of coverage in its header, but its only len of s call is before t0. The timed scan uses the saved n, so removal of the length cache in builtin_len is invisible to it.

Independently reproduced at 0c680102cfe6ac7f961c8a0eb76267a00fed0605. The only runtime mutation was:

 Value* builtin_len(Value *arg) {
@@
     if (arg->type == VAL_STR)
-        return make_num(val_str_len(arg));
+        return make_num(strlen(arg->data.strv.ptr));

I compiled that translation unit with the release recipe and linked it with the current release objects. No fake runtime, timing stub, environment replay, or altered gate was involved. The modified runtime returns the same lengths.

The untouched gate passed three times at 2.01, 2.01, 2.02 (rc 0). It would pass the former 2.60 threshold as well as 2.90. Meanwhile the real pre-#1185 indexing binary failed three times at 4.34, 4.52, 4.48; the instrument still detects that original regression.

To expose the missed class, I extracted the gate's actual scan program and changed only its loop condition from i < n to i < (len of s). Five interleaved release/mutant samples per length, JIT off, all child exits 0 and all scan counts correct:

Runtime 20k median ms 40k 80k Doubling ratios
Current release 12.023219 23.421235 48.285582 1.948, 2.062
builtin_len cache removed 38.151753 140.258292 471.863735 3.676, 3.364

This is a workload-coverage class, not a claim that changing the threshold caused this hole: a named operation used only in setup cannot contribute its complexity to the verdict. Add a separately timed len of-in-loop workload (with a real cache-removal fault control), or narrow the stated coverage explicitly. Retain separate indexing coverage rather than blending timings so one operation can dilute another.

Local reproduction artifacts: /tmp/strenrol-r4/real-regression.py, len-regression/commands.json, len-regression/mutation.diff, real-gate-results.json, scan-len.eigs, and len-loop-samples.json.

cd /home/jon/src/InauguralSystems/EigenScriptEcosystem/EigenScript
EIGS=/tmp/strenrol-r4/len-regression/eigenscript bash tests/test_string_scaling.sh
EIGS_JIT_OFF=1 /tmp/strenrol-r4/len-regression/eigenscript /tmp/strenrol-r4/scan-len.eigs 80000
Dominant language
C
Stars
3
Forks
7
Avg merge
3h 56m
Merged PRs (30d)
102

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