Messages in this thread | | | Date | Fri, 12 Aug 2022 21:06:31 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH 0/2] Optimize memchr() |
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Hi!
> This patche series optimized "memchr()" and add a macro for > "memchr_inv()" so that both funtions can use it to generate bit mask. > > The original implementaion of "memchr()" is based on byte-wise comparison, > which do not fully use 64-bit or 32-bit register in CPU. We implement a > word-wise comparison so that at least 4 bytes can be compared at the same > time. The optimized "memchr()" is nearly 4x faster than the original one > for long strings. In Linux Kernel, we find that the length of the string
Well... how much slower is it for short strings?
> searched by "memchr()" is up to 512 bytes in drivers/misc/lkdtm/heap.c. > In our test, the optimized version is about 20% faster if the target > character is at the end of the string when going through a 512-byte > string.
"What is the average length passed to memchr" would be more useful question.
Best regards, Pavel
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