From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,b23661223cdab88a
X-Google-Attributes: gid103376,public
From: davidf@mks.com (David J. Fiander)
Subject: Re: Representation clauses and records
Date: 1997/12/18
Message-ID: <u90tiqsmz.fsf@davidf-nt.mks.com>#1/1
X-Deja-AN: 299455222
Sender: davidf@davidf-nt.mks.com
References: <347000b1.4909762@news.geccs.gecm.com>
 <349646A2.1A013246@alphalink.com.au> <1997Dec16.061148.1@eisner>
 <34979C4A.3C2D3D71@alphalink.com.au>
Organization: Mortice Kern Systems Inc.
Newsgroups: comp.lang.ada
Date: 1997-12-18T00:00:00+00:00
List-Id: <comp.lang.ada>


Pascal MALAISE <malaise@alphalink.com.au> writes:
> As far as I know, this problem would not happen in full ADA because the
> instanciation of unchecked_conversion will be compiled as a call to
> something
> like memcpy, a procedure which does not make any assumption about
> alignment of arguments.
> We loose performance but gain reliability.

I've seen other comments that indicate that the runtime cost of a
call to Unchecked_Conversion is going to be a function call of
some sort, and I have just one question: "Why?"

It would seem to me that if I have an object of some sort, and I
call Unchecked_Conversion on it, if the type is small enough
(in C terms converting a pointer to an int), why shouldn't the
compiler just generate a "load ptr/store int" instruction
sequence?  Now, for larger objects, the compiler will have to
perform a block move to effect the conversion, either via a
runtime library call or by open-coding the block move, but that
depends entirely on the H/W support for block moves.

- David