Path: utzoo!utgpu!water!watmath!clyde!ima!johnl
From: johnl@ima.ISC.COM (John R. Levine)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Microsoft Assembler
Summary: Yes, dumb.
Keywords: assembler, branch optimization
Message-ID: <864@ima.ISC.COM>
Date: 27 Jan 88 16:40:46 GMT
References: <1428@homxb.UUCP>
Reply-To: johnl@ima.UUCP (John R. Levine)
Organization: Not enough to make any difference
Lines: 28

In article <1428@homxb.UUCP> gemini@homxb.UUCP (Rick Richardson) writes:
>We have a need to convert 8088 assembler code from an assembler
>that operates like most UNIX assemblers to the Microsoft Assembler.
>...
>The question is: is it possible to get [branch optimization] from the
>Microsoft 5.0 assembler?  is it possible to write a macro to do this?
>or is it just plain not possible with the Microsoft tools?

Generally speaking, you can't do it. MS assemblers have always done simple
branch optimization for backward unconditional branches, but not forward ones.
As a cruel joke, the 5.0 assembler puts out a warning "Jump within short
distance" when it notices a forward jump that it should have made short.
You're then supposed to stick a "short" keyword into the source code and
reassemble.

It gives you no help at all on conditional branches. I believe you could write
macros to optimize backward conditional branches, but you're out of luck again
for forward ones.  It will, of course, give you an error message if you try
to branch too far with a conditional jump, but it's up to you to fix the code.

Perhaps you could write a program which iteratively assembles a routine, then
looks at the error messages and adjusts the branches in the source code and
assembles it again until the error messages go away (up to some limit, there
are cases where the warning is unavoidable.)
-- 
John R. Levine, IECC, PO Box 349, Cambridge MA 02238-0349, +1 617 492 3869
{ ihnp4 | decvax | cbosgd | harvard | yale }!ima!johnl, Levine@YALE.something
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