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From: jdb@mordor.UUCP
Newsgroups: comp.arch
Subject: Re: Available no. of registers
Message-ID: <1302@mordor.s1.gov>
Date: Tue, 27-Jan-87 13:39:05 EST
Article-I.D.: mordor.1302
Posted: Tue Jan 27 13:39:05 1987
Date-Received: Wed, 28-Jan-87 21:14:38 EST
References: <3810002@nucsrl.UUCP> <926@mips.UUCP> <759@vaxb.calgary.UUCP> <213@ames.UUCP> <3510@amd.UUCP>
Reply-To: jdb@mordor.UUCP (John Bruner)
Organization: S-1 Project, LLNL
Lines: 25

>Oh, what a mess!!  One of the parts of C which is cleaned up in the ANSI
>draft standard is the use of casts to convert pointer values.  ...
>The only conversions that may be performed on pointers is
>to convert them to (void *) and back to the SAME type.  On some machines,
>the conversion to (char *) and back is possible, but this is implementation
>defined behavior, and not portable. 

*Implicit* pointer conversion (without casts) is only permitted between
a pointer to an object and a pointer to void.  However, the draft
ANSI standard (October 10, 1986, section 3.3.4) says that explicit
conversions between other pointer types is allowed:

	A pointer to an object of one type may be converted to a
	pointer to an object of another type.  The resulting pointer
	might not be valid if it is improperly aligned for the type
	of object pointed to.  It is guaranteed, however, that a
	pointer to an object of a given alignment may be converted
	to a pointer to an object of a less strict alignment and
	back again; the result shall compare equal to the original
	pointer.  (An object that has type char has the least
	strict alignment.)
-- 
  John Bruner (S-1 Project, Lawrence Livermore National Laboratory)
  MILNET: jdb@mordor.s1.gov		(415) 422-0758
  UUCP: ...!ucbvax!decwrl!mordor!jdb 	...!seismo!mordor!jdb