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| From | Mike Hore <mike_horeREM@OVE.invalid.aapt.net.au> |
|---|---|
| Newsgroups | comp.arch |
| Subject | Re: Q: bit shifting |
| Date | 2011-10-11 17:08 +1100 |
| Organization | A noiseless patient Spider |
| Message-ID | <j70mgu$s17$1@dont-email.me> (permalink) |
| References | <j6mnv4$8rt$1@news.albasani.net> <j6mn43$2ma$1@gosset.csi.cam.ac.uk> <4ui3m8-aa91.ln1@ntp6.tmsw.no> |
On 8/10/11 2:35 AM, Terje Mathisen wrote:
> ...
> Nick is absolutely correct here, bit shifts have been badly treated
> since day one.
>
> Most people would probably agree that a left shift (or logical right
> shift) of an N-wide register by N or more bits, should result in a zero.
>
> Likewise, arithmetic right shifts of the same size should give the sign
> bit replicated across the entire register.
>
> If you absolutely have to limit N, then make the limit no less than
> twice the register width. Masking the shift count is a really bad idea...
KDF9 nearly got it right. On a 48-bit word, or 96-bit doubleword, you
could specify a shift from -128 to +127, and get what you expected.
Positive shifts were left, negative shifts were right. Going outside
the limits gave "incorrect results with no warning" (from the Usercode
manual on Bitsavers).
Cheers, Mike.
---------------------------------------------------------------
Mike Hore mike_horeREM@OVE.invalid.aapt.net.au
---------------------------------------------------------------
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Q: bit shifting Mok-Kong Shen <mok-kong.shen@t-online.de> - 2011-10-07 13:31 +0200
Re: Q: bit shifting nmm1@cam.ac.uk - 2011-10-07 12:17 +0100
Re: Q: bit shifting Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-07 17:35 +0200
Re: Q: bit shifting Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2011-10-07 09:31 -0700
Re: Q: bit shifting nmm1@cam.ac.uk - 2011-10-07 17:16 +0100
Re: Q: bit shifting Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2011-10-07 23:13 -0700
Re: Q: bit shifting nmm1@cam.ac.uk - 2011-10-08 09:56 +0100
Re: Q: bit shifting Andrew Reilly <areilly---@bigpond.net.au> - 2011-10-08 21:28 +0000
Re: Q: bit shifting timcaffrey@aol.com (Tim McCaffrey) - 2011-10-11 15:05 +0000
Re: Q: bit shifting Sean Case <seancase@tpg.com.au> - 2011-10-16 23:15 +1000
Re: Q: bit shifting timcaffrey@aol.com (Tim McCaffrey) - 2011-10-19 20:12 +0000
Re: Q: bit shifting Robert Wessel <robertwessel2@yahoo.com> - 2011-10-07 12:24 -0500
Re: Q: bit shifting Kai Harrekilde-Petersen <khp@harrekilde.dk> - 2011-10-07 19:27 +0200
Re: Q: bit shifting Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-08 10:41 +0200
Re: Q: bit shifting Kai Harrekilde-Petersen <khp@harrekilde.dk> - 2011-10-08 11:28 +0200
Re: Q: bit shifting Andrew Reilly <areilly---@bigpond.net.au> - 2011-10-08 21:38 +0000
Re: Q: bit shifting Robert Wessel <robertwessel2@yahoo.com> - 2011-10-08 22:57 -0500
Re: Q: bit shifting Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-09 08:18 +0200
Re: Q: bit shifting Mok-Kong Shen <mok-kong.shen@t-online.de> - 2011-10-19 15:08 +0200
Re: Q: bit shifting Michael S <already5chosen@yahoo.com> - 2011-10-11 16:41 -0700
Re: Q: bit shifting Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-12 07:55 +0200
Re: Q: bit shifting MitchAlsup <MitchAlsup@aol.com> - 2011-10-12 10:21 -0700
Re: Q: bit shifting Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-12 21:22 +0200
Re: Q: bit shifting kenney@cix.compulink.co.uk - 2011-10-13 11:00 -0500
Re: Q: bit shifting Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-13 20:32 +0200
Re: Q: bit shifting Mike Hore <mike_horeREM@OVE.invalid.aapt.net.au> - 2011-10-11 17:08 +1100
Re: Q: bit shifting MitchAlsup <MitchAlsup@aol.com> - 2011-10-07 12:49 -0700
Re: Q: bit shifting nmm1@cam.ac.uk - 2011-10-07 21:20 +0100
The word is devolving into 3 architectures (NOT?) "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-10-07 19:48 -0700
Re: The word is devolving into 3 architectures (NOT?) Mark Thorson <nospam@sonic.net> - 2011-10-07 19:56 -0800
Re: The word is devolving into 3 architectures (NOT?) "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-10-08 04:53 +0200
Re: The word is devolving into 3 architectures (NOT?) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-10-08 17:26 +0000
Re: Q: bit shifting Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-08 10:47 +0200
Re: Q: bit shifting MitchAlsup <MitchAlsup@aol.com> - 2011-10-08 12:27 -0700
Re: Q: bit shifting Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-09 08:07 +0200
Re: Q: bit shifting MitchAlsup <MitchAlsup@aol.com> - 2011-10-09 12:36 -0700
Re: Q: bit shifting Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-10 09:06 +0200
Re: Q: bit shifting timcaffrey@aol.com (Tim McCaffrey) - 2011-10-10 15:31 +0000
Re: Q: bit shifting Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-10 18:13 +0200
Re: Q: bit shifting timcaffrey@aol.com (Tim McCaffrey) - 2011-10-10 20:27 +0000
Re: Q: bit shifting Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-10 23:45 +0200
Re: Q: bit shifting Robert Wessel <robertwessel2@yahoo.com> - 2011-10-10 17:32 -0500
Re: Q: bit shifting timcaffrey@aol.com (Tim McCaffrey) - 2011-10-11 14:58 +0000
Re: Q: bit shifting Robert Wessel <robertwessel2@yahoo.com> - 2011-10-11 11:30 -0500
Re: Q: bit shifting "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-10-11 10:05 -0700
Re: Q: bit shifting timcaffrey@aol.com (Tim McCaffrey) - 2011-10-11 17:59 +0000
Re: Q: bit shifting timcaffrey@aol.com (Tim McCaffrey) - 2011-10-11 18:00 +0000
Re: Q: bit shifting Al Grant <algrant@myrealbox.com> - 2011-10-11 13:49 -0700
Re: Q: bit shifting Al Grant <algrant@myrealbox.com> - 2011-10-11 14:18 -0700
Re: Q: bit shifting Robert Wessel <robertwessel2@yahoo.com> - 2011-10-11 16:03 -0500
Re: Q: bit shifting MitchAlsup <MitchAlsup@aol.com> - 2011-10-10 09:52 -0700
Re: Q: bit shifting anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-10-09 12:24 +0000
Re: Q: bit shifting nmm1@cam.ac.uk - 2011-10-09 13:13 +0100
Re: Q: bit shifting Quadibloc <jsavard@ecn.ab.ca> - 2011-10-09 10:11 -0700
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