Opcode fsub

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dmitriy566

Joined: 19 Jun 2012
Posts: 25
Location: Saint-Petersburg, Russia

dmitriy566 03 Jul 2012, 12:09

Hello!
When i insert only one command fsub in work code, fasm says:"invalid operand". With fsubp it works ok. I think that it is a bug.

03 Jul 2012, 12:09

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20401
Location: In your JS exploiting you and your system

revolution 03 Jul 2012, 12:28

If you read the Intel manual it states that fsub (without the p) must have either a memory operand or two st() operands, and that fsubp has no operands.

If you want to call it a bug then you need to talk to Intel about it.

03 Jul 2012, 12:28

dmitriy566

Joined: 19 Jun 2012
Posts: 25
Location: Saint-Petersburg, Russia

dmitriy566 03 Jul 2012, 15:09

Ok, if i write fsub st,st(1) , fasm says "extra characters on line". And as i know, fsub without operands equivalent fsub st,st(1).

03 Jul 2012, 15:09

dmitriy566

Joined: 19 Jun 2012
Posts: 25
Location: Saint-Petersburg, Russia

dmitriy566 03 Jul 2012, 16:16

And as i see, analogical behaviour have opcodes fadd,fmul,fdiv and reverse operations(fsubr and others).

03 Jul 2012, 16:16

CandyMan

Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop

CandyMan 03 Jul 2012, 16:19

use

Code:

FSUB ST,ST1 instead of: FSUB ST,ST(1)

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03 Jul 2012, 16:19

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20401
Location: In your JS exploiting you and your system

revolution 04 Jul 2012, 07:48

dmitriy566 wrote:

And as i know, fsub without operands equivalent fsub st,st(1).

Perhaps you are thinking of another assembler that does this? There is nothing stated in the CPU manuals to show this equivalence.

04 Jul 2012, 07:48

dmitriy566

Joined: 19 Jun 2012
Posts: 25
Location: Saint-Petersburg, Russia

dmitriy566 06 Jul 2012, 12:19

Thank you very much!

06 Jul 2012, 12:19

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