From: mg@dsd.camb.inmet.com (Mitch Gart)
Subject: Re: Ada Portability... NOT!
Date: Mon, 21 Nov 1994 14:59:10 GMT
Date: 1994-11-21T14:59:10+00:00 [thread overview]
Message-ID: <CzMHMn.3uG@inmet.camb.inmet.com> (raw)
In-Reply-To: 199411182104.PAA04854@mail.cs.utexas.edu
One point was implied by Robert's response but wasn't stated
explicitly. On the HP RISC architecture, if a program
directly references a mis-aligned piece of data (a 4 byte
quantity aligned on < 4 bytes, or an 8 byte quantity aligned
on < 8 bytes) the machine will trap. This means that at execution
time either
- the program will crash
- the program will get CONSTRAINT_ERROR
- the compiler will have to generate lots of extra instructions
to "fiddle" as Robert says, that is, to fetch a quantity a
few bytes at a time, and put it together into the right
data format, then execute some more extra instructions later
when storing the data back into memory.
The fact that the compiler did none of the above, and instead
rejected the rep clause, seems like a reasonable thing to have
done on the HP machine.
Mitch Gart
next prev parent reply other threads:[~1994-11-21 14:59 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
1994-11-18 21:04 Ada Portability... NOT! Capt. Britt Snodgrass
1994-11-19 16:55 ` Robert Dewar
1994-11-21 2:11 ` Carlos Perez
1994-11-21 13:17 ` Robert Dewar
1994-11-21 23:56 ` Keith Thompson
1994-11-22 3:53 ` Robert Dewar
1994-11-23 12:49 ` Michael J. Meier
1994-11-24 19:21 ` R_Tim_Coslet
1994-11-20 1:33 ` Carlos Perez
1994-11-21 5:06 ` Niklas Holsti
1994-11-21 16:19 ` Norman H. Cohen
1994-11-21 14:59 ` Mitch Gart [this message]
1994-11-21 15:40 ` Michael J. Meier
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