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feda2297b7
This changeset adds both a scalar and an x86-64-v2 implementation of the strcspn(3) function to libc. A baseline implementation does not appear to be feasible given the requirements of the function. The scalar implementation is similar to the generic libc implementation, but expands the bit set into a byte set to reduce latency, improving performance. This approach could probably be backported to the generic C version to benefit other platforms. The x86-64-v2 implementation is built around the infamous pcmpistri instruction. An alternative implementation based on the Muła/Langdale algorithm [1] was prototyped, but performed worse than the pcmpistri approach except for sets of more than 16 characters with long input strings. All implementations provide special cases for the empty set (reduces to strlen as well as single-character sets (reduces to strchr). The x86-64-v2 kernel falls back to the scalar implementation for sets of more than 32 characters. This limit could be raised by additional multiples of 16 through the use of additional pcmpistri code paths, but I consider this case to be too rare to be of importance. This includes the bug fix from 52d4a4d. [1]: http://0x80.pl/articles/simd-byte-lookup.html Sponsored by: The FreeBSD Foundation Approved by: mjg MFC after: 1 week MFC to: stable/14 Differential Revision: https://reviews.freebsd.org/D41557 (cherry picked from commit 474408bb7933f0383a0da2b01e717bfe683ae77c) (cherry picked from commit 52d4a4d4e0dedc72bc33082a3f84c2d0fd6f2cbb) |
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| .. | ||
| amd64_archlevel.c | ||
| bcmp.S | ||
| bcopy.c | ||
| bzero.c | ||
| Makefile.inc | ||
| memcmp.S | ||
| memcpy.S | ||
| memmove.S | ||
| memset.S | ||
| stpcpy.S | ||
| strcat.S | ||
| strchrnul.S | ||
| strcmp.S | ||
| strcpy.c | ||
| strcspn.S | ||
| strlen.S | ||