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Replace utf8.DecodeRuneInString + unicode.IsLetter in the identifier scan hot loop with 128-entry byte-indexed table lookups for ASCII bytes. Non-ASCII bytes (>= 0x80) still fall through to the unicode-aware path. identStartTable[c]: true for a-z A-Z _ identContTable[c]: true for a-z A-Z 0-9 _ +22% serial throughput on Apple M4: 43.9 → 53.6 MB/s in-memory. Parallel: 220.8 → 240.3 MB/s.
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Summary
utf8.DecodeRuneInString+unicode.IsLetterin the identifier scan hot loop with 128-entry byte-indexed lookup tables for ASCII bytesidentStartTable[128]bool: a-z A-Z _identContTable[128]bool: a-z A-Z 0-9 _Throughput (Apple M4, 10 cores, in-memory benchmark)
+22% on serial; +9% on parallel. Wall-clock
gopapy bench corpus/src: 262 MB/s (25.7x CPython).Test plan
go test ./...passes