Article View: comp.arch
Article #21323Re: Understanding variations in Dhrystone performance
From: Earl Culham
Date: Wed, 17 May 1989 18:00
Date: Wed, 17 May 1989 18:00
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1224 bytes
In article <1989May15.173631.3029@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes:
<In article <474@estevax.UUCP> wck353@estevax.UUCP (HrDr Weicker Reinhold ) writes:
<>... Note that
<>processors with an instruction that checks a word for a null byte (such
<>as AMD's 29000 and Intel's 80960) have an advantage here...
<
<Only a small one; you can do the same check on a machine without the
<fancy instruction by being clever. Consider:
<
< (((x & ~0x80808080) - 0x01010101) & 0x80808080)
<
<The result is nonzero if, and only if, there was a NUL byte in x.
EEEEEEEEEEEEEEE
Actually, this also causes a false trigger if any byte contains
X'80'.
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arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!att!alberta!uqv-mts!ualtavm.bitnet!ECULHAMReferences:
<474@estevax.UUCP> <1989May15.173631.3029@utzoo.uucp>Show Full Headers
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!att!alberta!uqv-mts!ualtavm.bitnet!ECULHAM From: ECULHAM@UALTAVM.BITNET (Earl Culham) Newsgroups: comp.arch Subject: Re: Understanding variations in Dhrystone performance Message-ID: <483@UALTAVM.BITNET> Date: 17 May 89 18:00:04 GMT References: <474@estevax.UUCP> <1989May15.173631.3029@utzoo.uucp> Reply-To: ECULHAM@UALTAVM.BITNET Organization: University of Alberta VM/CMS Lines: 17 Disclaimer: Author bears full responsibility for contents of this article