Optimize strspn() #12431
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Optimize strspn() #12431
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The current implementation uses a nested loop (for + goto), which has complexity O(|s1| * |s2|). If we instead use a lookup table, the complexity drops to O(|s1| + |s2|). This is conceptually the same strategy that common C library implementations such as glibc and musl use. The variation with a bitvector instead of a table also gives a speed-up, but the table variation was about 1.34x faster. On microbenchmarks this easily gave a 5x speedup. This can bring a 1.4-1.5% performance improvement in the Symfony benchmark.
Girgias
approved these changes
Oct 14, 2023
Agreed, fixed in the merge, thx |
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The current implementation uses a nested loop (for + goto), which has complexity O(|s1| * |s2|). If we instead use a lookup table, the complexity drops to O(|s1| + |s2|).
This is conceptually the same strategy that common C library implementations such as glibc and musl use.
The variation with a bitvector instead of a table also gives a speed-up, but the table variation (i.e. this one) was about 1.34x faster.
On microbenchmarks this easily gave a 5x speedup.
This can bring a 1.4-1.5% performance improvement in the Symfony benchmark.