Efficiency of code generated by Ada compilers
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From: Yannick Duchêne (Hibou57) on 13 Aug 2010 18:43 > When you are talking about hardware level checks, are you talking about > check for null address divide par zero and so on or something else ? I > have never heard about a machine with a level array type and an hardware > check for array access index. Would be interesting if you could be more > explicit about these hardware checks. Well, I know about some CPU with low level capabilities to check for read access to unassigned/not-initialized memory location.
From: tmoran on 13 Aug 2010 19:29 >have never heard about a machine with a level array type and an hardware >check for array access index. Would be interesting if you could be more The Burroughs machines were like that. The descriptor pointing to an array included the size as well as the base address, so index in-range was automatically checked by the hardware.
From: Yannick Duchêne (Hibou57) on 13 Aug 2010 20:02 Le Sat, 14 Aug 2010 01:29:56 +0200, <tmoran(a)acm.org> a écrit: > The Burroughs machines were like that. The descriptor pointing to > an array included the size as well as the base address, so index in-range > was automatically checked by the hardware. So these old machines were in some way safer than ones of nowadays A similar thing exist with Intel CPUs : memory segment are defined using a base and a limit. This may be feasible to assign a memory segment to each array and then get the same check done (an hardware exception would be raised if ever an attempt to access a byte beyond the limit was maid), while this would come with a cost, at least the one to have to switch memory segment register all the time (this is more costly than reading and writing any other register). I found a nice page about Burroughs machines and others: http://www.cs.virginia.edu/brochure/museum.html Nice historical document Near the bottom a the page, an photo of a pins labeled âI touched a B5000â (which as the page said, was one of these Burroughs machines) If you go down into the page, there is another picture, of an addressable magnetic tape containing the Nicklaus Wirth's Pascal compiler (touching, if I may say so)
From: (see below) on 13 Aug 2010 20:16
On 14/08/2010 01:02, in article op.vheielzsule2fv(a)garhos, "Yannick Duch�ne (Hibou57)" <yannick_duchene(a)yahoo.fr> wrote: > Le Sat, 14 Aug 2010 01:29:56 +0200, <tmoran(a)acm.org> a �crit: >> The Burroughs machines were like that. The descriptor pointing to >> an array included the size as well as the base address, so index in-range >> was automatically checked by the hardware. > So these old machines were in some way safer than ones of nowadays Burroughs-architecture m/cs should not be referred to in the past tense. They still sell very profitably. -- Bill Findlay <surname><forename> chez blueyonder.co.uk |