Re: newbie: MUL product

Brian wrote:
On Thu, 29 Mar 2007 19:16:31 +0200, Herbert Kleebauer <klee@xxxxxxxxx>
wrote:


Wolfgang Kern wrote:


or the immediate operand IMUL forms:

anyreg32=anyreg/mem32 * SXimm8/imm32

ie: IMUL eax,ebx,-09

(unfortunately no unsigned MUL in this forms)

Maybe you should use an other assembler which allows you to define the alias MUL for this IMUL instruction.
Or directly code it in HEX, if you use uppercase letters,
the CPU does an unsigned multiply (try it and you will
see it works):

00000000: 69 c3 fffffff7 muls.l #-9,r3,r0
00000006: 69 C3 FFFFFFF7 mulu.l #4294967287,r3,r0


Thanks Herbert, but to switch to another assembler would seem
counter-productive for me at this point, as I'm a complete newbie, and
I mainly want to learn "one" assembler at this point.

Good plan!

I gather from a few of your posts that you feel all assembly
programmers should learn machine code?

The truth of the matter is that we've gotten ourselves into such a fucking "Tower of Babel" situation that machine code is about the only way we can communicate! Unlike C, which has "standards" to say what's C and what's not, asm is less authoritarian and more flexible. This is nice. I like Nasm - the syntax isn't quite the same as Masm/Tasm (almost the same), but I *like* the changes. Herbert doesn't like Intel syntax - feel's it's illogical, and his 68K-style syntax is more logical and more regular. He may be right. He can do it that way, and does. Everybody can have the syntax he/she wants. But there's a price to pay!!!

Interesting what you say about the caps. While I didn't code this in
Hex, I did take a look at the dissassembly, and mine appears to use
different opcodes for mul and imul. Maybe that's a Motorola's 68k
assembly implementation that works for you?

I don't know if Herbert's jokin' or tripin', but in this case you shouldn't take his comment seriously. The CPU does not know what "case" the bytes are in, I assure you! (normally, you *can* trust what Herbert says - in spite of... maybe because of... his weird syntax, he knows his stuff)

There really are different opcodes for "imul eax, ebx, -9"...

00000000 69C3F7FFFFFF imul eax,ebx,dword 0xfffffff7
00000006 6BC3F7 imul eax,ebx,byte -0x9

.... but I don't think that's what Herbert was getting at. These both do a signed multiply - it's just a different way to write "-9". I don't know *what* Herbert was getting at! I can't figure out how to write a lowercase "3" to try it! :)

Best,
Frank
.

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