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Date:   Sat, 28 May 2022 16:12:34 +0800
From:   Yu-Jen Chang <>
        Yu-Jen Chang <>
Subject: [PATCH 0/2] x86: Optimize memchr() for x86-64 

*** BLURB HERE ***
These patch series add an optimized "memchr()" for x86-64 and 
There exists an assemebly implementation for x86-32. However, 
for x86-64, there isn't any optimized version. We implement word-wise 
comparison so that 8 characters can be compared at the same time on 
x86-64 CPU. The optimized “memchr()” is nearly 4x faster than the 
orginal implementation for long strings.

We test the optimized “memchr()” in UML and also recompile the 5.18 
Kernel with the optimized “memchr()”. They run correctly.

In this patch we add a new file "string_64.c", which only contains 
"memchr()". We can add more optimized string functions in it in the 

Yu-Jen Chang (2):
  x86/lib: Optimize memchr()
  x86/um: Use x86_64-optimized memchr

 arch/x86/include/asm/string_64.h |  3 ++
 arch/x86/lib/Makefile            |  1 +
 arch/x86/lib/string_64.c         | 78 ++++++++++++++++++++++++++++++++
 arch/x86/um/Makefile             |  2 +-
 4 files changed, 83 insertions(+), 1 deletion(-)
 create mode 100644 arch/x86/lib/string_64.c


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