Strangeness with xor operator in constants expression

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bazizmix

Joined: 15 Jan 2016
Posts: 51

bazizmix 04 Feb 2018, 12:30

flat assembler version 1.72
Simple text:

Code:

ZZZ equ 1
mov eax,-1 xor ZZZ
mov eax,ZZZ xor -1

and produced code:

Code:

B8 00 00 00 00 | mov eax,0         <-- wrong
B8 FE FF FF FF | mov eax,FFFFFFFE  <-- right

But!!!

Code:

ZZZ equ 2
mov eax,-1 xor ZZZ
mov eax,ZZZ xor -1

all OK:

Code:

B8 FD FF FF F | mov eax,FFFFFFFD
B8 FD FF FF F | mov eax,FFFFFFFD

04 Feb 2018, 12:30

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 19873
Location: In your JS exploiting you and your system

revolution 04 Feb 2018, 13:03

Unary minus has a lower precedence than xor. You can put brackets around the leading minus to force what you need.

Code:

mov eax,(-1) xor ZZZ

Last edited by revolution on 04 Feb 2018, 13:48; edited 1 time in total

04 Feb 2018, 13:03

bazizmix

Joined: 15 Jan 2016
Posts: 51

bazizmix 04 Feb 2018, 13:27

Thanks, revolution!

04 Feb 2018, 13:27

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