From: Philip Blundell <pb@nexus.co.uk>
To: David Woodhouse <Dave@imladris.demon.co.uk>
Cc: Meelis Roos <mroos@tartu.cyber.ee>, linux-kernel@vger.rutgers.edu
Subject: Re: faster strcpy()
Date: Fri, 24 Apr 1998 11:26:09 +0100 [thread overview]
Message-ID: <E0ySfgI-0006zV-00@spring.nexus.co.uk> (raw)
In-Reply-To: Your message of "Fri, 24 Apr 1998 11:14:34 +0200." <E0ySfV5-00058I-00@imladris.demon.co.uk>
>It's something like subtracting 0x01010101 from the dword and oring with
>0x80808080 to detect the carry, but that's not quite it. Perhaps you do
/* The following magic check was designed by A. Mycroft. It yields a */
/* nonzero value if the argument w has a zero byte in it somewhere. The */
/* messy constants have been unfolded a bit in this code so that they */
/* get preloaded into registers before relevant loops. */
#ifdef _copywords
# define ONES_WORD 0x01010101
# define EIGHTS_WORD (ones_word << 7)
# define nullbyte_prologue_() \
int ones_word = ONES_WORD;
# define word_has_nullbyte(w) (((w) - ones_word) & ~(w) & EIGHTS_WORD)
#endif
p.
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next parent reply other threads:[~1998-04-24 10:23 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <E0ySfV5-00058I-00@imladris.demon.co.uk>
1998-04-24 10:26 ` Philip Blundell [this message]
1998-04-25 22:44 ` Alexander Kjeldaas
[not found] ` <19980426013108.48608@lucifer.guardian.no>
1998-04-26 15:17 ` Pavel Machek
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