The patch titled
Subject: lib/bcd: optimize _bin2bcd() for improved performance
has been added to the -mm mm-nonmm-unstable branch. Its filename is
lib-bcd-optimize-_bin2bcd-for-improved-performance.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/lib-bcd-optimize-_bin2bcd-for-improved-performance.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Kuan-Wei Chiu <visitorckw@xxxxxxxxx>
Subject: lib/bcd: optimize _bin2bcd() for improved performance
Date: Tue, 13 Aug 2024 01:02:29 +0800
The original _bin2bcd() function used / 10 and % 10 operations for
conversion. Although GCC optimizes these operations and does not generate
division or modulus instructions, the new implementation reduces the
number of mov instructions in the generated code for both x86-64 and ARM
architectures.
This optimization calculates the tens digit using (val * 103) >> 10, which
is accurate for values of 'val' in the range [0, 178]. Given that the
valid input range is [0, 99], this method ensures correctness while
simplifying the generated code.
Link: https://lkml.kernel.org/r/20240812170229.229380-1-visitorckw@xxxxxxxxx
Signed-off-by: Kuan-Wei Chiu <visitorckw@xxxxxxxxx>
Cc: Ching-Chun (Jim) Huang <jserv@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/bcd.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/lib/bcd.c~lib-bcd-optimize-_bin2bcd-for-improved-performance
+++ a/lib/bcd.c
@@ -10,6 +10,8 @@ EXPORT_SYMBOL(_bcd2bin);
unsigned char _bin2bcd(unsigned val)
{
- return ((val / 10) << 4) + val % 10;
+ const unsigned int t = (val * 103) >> 10;
+
+ return (t << 4) | (val - t * 10);
}
EXPORT_SYMBOL(_bin2bcd);
_
Patches currently in -mm which might be from visitorckw@xxxxxxxxx are
lib-bcd-optimize-_bin2bcd-for-improved-performance.patch
