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<title>kernel/arch/powerpc/lib/strlen_32.S, branch linux-6.2.y</title>
<subtitle>Hosts the 0x221E linux distro kernel.</subtitle>
<id>https://universe.0xinfinity.dev/distro/kernel/atom?h=linux-6.2.y</id>
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<updated>2018-08-07T11:49:30Z</updated>
<entry>
<title>powerpc/lib: Implement strlen() in assembly for PPC32</title>
<updated>2018-08-07T11:49:30Z</updated>
<author>
<name>Christophe Leroy</name>
<email>christophe.leroy@c-s.fr</email>
</author>
<published>2018-08-01T09:01:14Z</published>
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<id>urn:sha1:9412b234501eef1d273cc759387a232f0027c574</id>
<content type='text'>
The generic implementation of strlen() reads strings byte per byte.

This patch implements strlen() in assembly based on a read of entire
words, in the same spirit as what some other arches and glibc do.

On a 8xx the time spent in strlen is reduced by 3/4 for long strings.

strlen() selftest on an 8xx provides the following values:

Before the patch (ie with the generic strlen() in lib/string.c):

  len 256 : time = 1.195055
  len 016 : time = 0.083745
  len 008 : time = 0.046828
  len 004 : time = 0.028390

After the patch:

  len 256 : time = 0.272185 ==&gt; 78% improvment
  len 016 : time = 0.040632 ==&gt; 51% improvment
  len 008 : time = 0.033060 ==&gt; 29% improvment
  len 004 : time = 0.029149 ==&gt; 2% degradation

On a 832x:

Before the patch:

  len 256 : time = 0.236125
  len 016 : time = 0.018136
  len 008 : time = 0.011000
  len 004 : time = 0.007229

After the patch:

  len 256 : time = 0.094950 ==&gt; 60% improvment
  len 016 : time = 0.013357 ==&gt; 26% improvment
  len 008 : time = 0.010586 ==&gt; 4% improvment
  len 004 : time = 0.008784

Signed-off-by: Christophe Leroy &lt;christophe.leroy@c-s.fr&gt;
Signed-off-by: Michael Ellerman &lt;mpe@ellerman.id.au&gt;
</content>
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