Path: utzoo!attcan!uunet!super!udel!rochester!rutgers!mailrus!ncar!noao!asuvax!fbog!dbk
From: dbk@fbog.UUCP (Dave B. Kinzer @ Price Rd. GEG)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Adjusting the stack pointer
Summary: Correct usage
Keywords: assembler A7 SP
Message-ID: <1667@fbog.UUCP>
Date: 22 Dec 88 17:21:37 GMT
References: <5047@garfield.MUN.EDU>
Reply-To: dbk@fbog.UUCP (Dave B. Kinzer @ Price Rd. GEG)
Followup-To: comp.sys.amiga.tech
Distribution: na
Organization: Motorola Microcomputer Division, Tempe, Az.
Lines: 40

In article <5047@garfield.MUN.EDU> john13@garfield.MUN.EDU (John Russell) writes:
>Manx-generated code uses the form
>
>addq.w #(4*N),sp
>     ^
>
>to reset the stack pointer after calling a function with N (long) args on the 
>stack.  Examples which adhere to the syntax of other Amiga assemblers use
>
>addq.l #(4*N),sp
>     ^
>
>Is the Manx format dangerous if the stack is being incremented past a
>64k boundary? Is there a reason to use one and not the other?
>
>John

Hey, something I know about! :-)

 Whenever the 68000 does anything with an address register as the destination,
the source is expanded to 32 bits before the operation is performed, always
in 32 bit mode.  This is true, for example, for add, load, and subtract.
The trick is you need to look in the 68000 manual under ADDA, MOVEA,
and SUBA (etc.)  Most assemblers will automatically change the instruction
generated based upon the destination address.  The book doesn't.

 The Manx generated code is faster (fewer instruction fetches from memory).


"The highly regular structure of the M68000 greatly simplifies the effort
required to write programs in assembly language as well as high level
languages." - M68000 16/32-bit Microprocessor Programmer's Reference 
Manual, fourth edition

-Yea, right.   (Note: sarcasm)


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