perf: optimize parse_string_to_decimal (30-40% faster)#4916
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mbutrovich merged 2 commits intoJul 22, 2026
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parse_string_to_decimal (30-40% faster)
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July 14, 2026 14:47
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First pass, thanks @andygrove!
…w10_i128 Deletes benches/cast_string_to_decimal.rs and folds its improvements (seeded StdRng, 8192-row batch, decimal_18_2) into the existing create_decimal_cast_string_batch in cast_from_string.rs so the two benches no longer collide on the same criterion group. Also drops the [[bench]] entry from Cargo.toml. Locks the 38-digit boundary that digits_to_i128's head/tail split relies on with three Rust unit tests: 38 nines parses, 39 nines overflows, 38 leading zeros plus '42' reduces to 42. Makes pow10_i128 return Option<i128> so an over-long fractional part maps to the invalid_decimal_cast error instead of the debug panic from 10_i128.pow(40).
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This LGTM after revision, thanks @andygrove!
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Which issue does this PR close?
N/A
Rationale for this change
Optimize existing expression.
What changes are included in this PR?
Replaced six redundant scans plus two str::parse calls with a single validating byte pass and direct i128 digit accumulation, gated the seven inf/nan string comparisons behind a first-byte check, and swapped 10_i128.pow for a const power-of-ten table.
How are these changes tested?
Existing tests.
Benchmark (criterion):
Full criterion output: