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[Bug libc/5807] strlen() not effective
- From: "carlos at codesourcery dot com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sources dot redhat dot com
- Date: 2 Mar 2008 03:29:47 -0000
- Subject: [Bug libc/5807] strlen() not effective
- References: <20080229004244.5807.egmont@gmail.com>
- Reply-to: sourceware-bugzilla at sourceware dot org
------- Additional Comments From carlos at codesourcery dot com 2008-03-02 03:29 -------
The math is wrong.
It looks glibc has a broken version of Alan Mycroft's HAKMEMC postings.
See: http://www.cl.cam.ac.uk/~am21/progtricks.html
The solution is "((x - 0x01010101) & ~x & 0x80808080)", but the "& ~x" is
missing from the glibc version.
The "#if 0" was added Tue Jan 21 03:39:54 1992 UTC (16 years, 1 month ago) by
roland, and the patch looked like this:
http://sources.redhat.com/cgi-bin/cvsweb.cgi/libc/sysdeps/generic/Attic/strlen.c.diff?r1=1.1&r2=1.2&cvsroot=glibc
I can reproduce this on cvs head. The generic strlen function is horribly
inefficient.
Roland can you comment on this?
What's the legal status of using that algorithm?
--
What |Removed |Added
----------------------------------------------------------------------------
AssignedTo|drepper at redhat dot com |roland at redhat dot com
Status|NEW |ASSIGNED
http://sourceware.org/bugzilla/show_bug.cgi?id=5807
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