From:	CSBVAX::MRGATE!SUTTON%BRANDEIS.BITNET@CUNYVM.CUNY.EDU@SMTP 19-MAR-1988 14:13
To:	ARISIA::EVERHART
Subj:	RE: Chaining images... THE source


Received: from MITVMA.MIT.EDU by KL.SRI.COM with TCP; Fri 18 Mar 88 13:25:12-PST
Received: from BRANDEIS.BITNET by MITVMA.MIT.EDU ; Fri, 18 Mar 88 16:24:50 EST
Date:     Fri, 18 Mar 88 16:22 EST
From:     <SUTTON%BRANDEIS.BITNET@MITVMA.MIT.EDU>
Subject:  RE: Chaining images... THE source
To:       info-vax@kl.sri.com
X-Original-To:  com%"info-vax@kl.sri.com", SUTTON

I got a message a few minutes ago (I wonder how many days it will be before
this message gets to people), saying that it is not possible in a practical
sense to "chain images".  That is, "CALL" one image from another as if it
were just a subroutine.  I didn't think it was possible either until a
message came in referring everyone to the LIB$FIND_IMAGE_SYMBOL routine (my
apologies to the person who posted it, I don't remember your name).  I
wanted to see if it REALLY did what the manual seemed to say it did
(sometimes the routine descriptions which don't include examples are vague
or I'm simply too dumb to understand without an example).  I looked in the
Master Index to see if there were any references to the routine other than
the description in the RTL manual.  There were none and therefore no
examples (I assume) in the manuals.  So I went to the sources (the micro
fiche) for clues and found two simple examples in the comments to the
routine which convince me of the utility of the routine.  Here's a
transcript of what it says:

--------------------------------------------------------------------------------
EXAMPLES:

a) Using LIB$FIND_IMAGE_SYMBOL from BLISS

    STATUS = LIB$FIND_IMAGE_SYMBOL($DESCRIPTOR('EDTSHR'),
                                   $DESCRIPTOR('EDT$EDIT'),
                                   EDTADDR);
    (.EDTADDR)($DESCRIPTOR('FOO.INP'), $DESCRIPTOR('FOO.OUT'));

b) Using LIB$FIND_IMAGE_SYMBOL from FORTRAN

    CALL LIB$FIND_IMAGE_SYMBOL('EDTSHR','EDT$EDIT',EDTADDR)
    CALL USER_CALL_SYMBOL(EDTADDR,%VAL(num_args),arg1,arg2,...)

        where USER_CALL_SYMBOL is the following MACRO routine:
            .ENTRY  USER_CALL_SYMBOL, 0

            MOVL    @4(AP),R0   ;Get address to call
            CALLG   8(AP),(R0)  ;Call the routine
            RET                 ;Return with status in R0
--------------------------------------------------------------------------------

SUTTON@BRANDEIS.BITNET