fix: speed up splitLimitR long delimiter search#1063
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Motivation: std.splitLimitR scanned backward with repeated prefix comparisons, so long delimiters with shared prefixes could degrade to O(N*M) per lookup and show release-regression risk versus 0.6.3. Modification: Add a bounded direct-probe fast path plus reverse-KMP fallback for multi-character right splits, keep the zero-split fast path O(1), and add regression coverage/bench data. Result: New split_limit_r_long_delim JMH case improves from 12.636 ms/op on master and 5.087 ms/op on 0.6.3 to 1.522 ms/op. Guardrail reverse delimiter stays at parity with master.
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Motivation: std.splitLimitR should avoid unnecessary reverse-KMP setup when a delimiter cannot fit, and the optimized path needs direct coverage for the KMP fallback. Modification: Return the original string before bounded/KMP setup when the delimiter is longer than the input. Add splitLimitR tests for the long-delimiter case, the unbounded maxsplits path, and a case that forces the KMP fallback after naive probes. Result: Preserves splitLimitR semantics while removing avoidable work and pinning the optimized fallback paths with tests.
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Motivation
std.splitLimitRcan spend too much time searching for long multi-character delimiters with repeated prefixes. No-match inputs such as a long string ofacharacters with delimiteraaaaaaaaabrepeatedly re-check the same characters.Modification
Result
std.length(std.splitLimitR(importstr "long-a.txt", "aaaaaaaaab", 1))111, slower repeated probing1, reverse-KMP fallbackO(N*M)per lookupO(N+M)per lookupThe PR keeps the observable split result unchanged and improves the pathological search path.
Risks
std.splitLimitR.