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perf: toStringAs appends digits and reverses once - #7
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table.insert(t, 1, digit) shifts the whole accumulated table on every loop iteration — quadratic in the digit count (bounded at 32 for Int, so a constant-factor cost in practice). Append least-significant-first and reverse the joined string instead; each digit is a single ASCII byte, so string reverse is safe for every radix up to 36. Measured 1.5-1.6x on 31-digit binary rendering (LuaJIT and PUC 5.1). Refs purescript-lua/purescript-lua#186.
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Problem
toStringAsbuilt its digit sequence withtable.insert(t, 1, digit), shifting the whole accumulated table on every loop iteration, quadratic in the digit count. ForIntthe digit count is bounded (at most 32 in radix 2), so in practice this is a constant-factor cost on a hot formatting path rather than an asymptotic blowup. Flagged by the fork-FFI performance audit, purescript-lua/purescript-lua#186.Change
Digits come out of the division loop least-significant first; append them and reverse the joined string once. Each digit is a single ASCII byte for every radix up to 36, so
string.reversecannot split a character. Output is unchanged.Verification
scripts/testis green: all 71 regression checks, including the multi-digit, negative and max-InttoStringAscases that pin digit order (a reversal mistake flips100into001). Measured on 31-digit binary rendering (toStringAs 2 2147483647, 2·10⁵ reps): 1.5× faster under LuaJIT (0.355 s → 0.240 s), 1.6× under PUC Lua 5.1 (1.634 s → 0.992 s).Suggested release: patch (v6.1.3) plus a package-set bump.
Refs purescript-lua/purescript-lua#186.