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From: gea%Romeo@cit-hamlet.arpa
Newsgroups: net.lang.c
Subject: Register short
Message-ID: <66@brl-tgr.ARPA>
Date: Tue, 26-Nov-85 02:14:11 EST
Article-I.D.: brl-tgr.66
Posted: Tue Nov 26 02:14:11 1985
Date-Received: Wed, 27-Nov-85 05:47:18 EST
Sender: news@brl-tgr.ARPA
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    Actually, 'register short' can be a useful construct if your compiler
knows what to do with it.  I had a loop doing a checksum and wanted to keep
the sum in a register.  If I declared it as 'register int' (this is on a
VAX), I got code looking like:

     ; R11 = pointer to array of shorts to be checksummed
     ; R10 = working sum

     CVTWL (R11)+,R0
     ADDL2 R10,R0

whereas if I declared the sum as 'register short' the loop body was

     ADDW2 R10,(R11)+

[Apologies if my assembler syntax isn't perfect, it's been a while -- and I
know these don't produce exactly the same result, but I had a short to store
the checksum in, so the second was actually what I wanted].

    The point is that there can be some benefit to compilers supporting
'register short' and 'register char' -- a lot of unnecessary conversions
can be eliminated.  (This was done on a VMS machine using INTERactive
Systems' compiler).

				Gary Ansok