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Improve generic strspn performance
As for strcspn, this patch improves strspn performance using a much faster algorithm. It first constructs a 256-entry table based on the accept string and then uses it as a lookup table for the input string. As for strcspn optimization, it is generally at least 10 times faster than the existing implementation on bench-strspn on a few AArch64 implementations. Also the string/bits/string2.h inlines make no longer sense, as current implementation will already implement most of the optimizations. Tested on x86_64, i686, and aarch64. * string/strspn.c (strcspn): Rewrite function. * string/bits/string2.h (strspn): Use __builtin_strcspn. (__strspn_c1): Remove inline function. (__strspn_c2): Likewise. (__strspn_c3): Likewise. * string/string-inlines.c [SHLIB_COMPAT(libc, GLIBC_2_1_1, GLIBC_2_24)] (__strspn_c1): Add compatibility symbol. [SHLIB_COMPAT(libc, GLIBC_2_1_1, GLIBC_2_24)] (__strspn_c2): Likewise. [SHLIB_COMPAT(libc, GLIBC_2_1_1, GLIBC_2_24)] (__strspn_c3): Likewise.
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