negative value bug?

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bitshifter

Joined: 04 Dec 2007
Posts: 796
Location: Massachusetts, USA

bitshifter 22 Nov 2011, 12:16

I was playing around with some code i posted in main
and decided to throw some negative values at it for fun.
Tested on versions 1.69.14 and 1.69.35 with same result:

Code:

org 0x0100
use16

  mov bx,-1                     ;bug?
  call display_bin16

  mov bx,1                      ;bug?
  neg bx
  call display_bin16

  mov bx,0
  mov bh,-1                     ;bug?
  call display_bin16

  mov bx,0
  mov bl,-1                     ;bug?
  call display_bin16

  mov bx,0x81                   ;ok
  call display_bin16

  mov bx,129                    ;ok
  call display_bin16

  mov bx,10000001b              ;ok
  call display_bin16

  mov bx,not 0x7ffe             ;ok
  call display_bin16

  mov bx,0x8001                 ;ok
  call display_bin16

  mov bx,32769                  ;ok
  call display_bin16

  mov bx,1000000000000001b      ;ok
  call display_bin16

  xor ah,ah
  int 0x16
  ret

display_bin16:
  mov cx,16
  mov ah,0x02
display_bin16_loop:
  xor dx,dx
  shl bx,1
  adc dl,'0'
  int 0x21
  loop display_bin16_loop
  mov dl,0x0d
  int 0x21
  mov dl,0x0a
  int 0x21
  ret

_________________
Coding a 3D game engine with fasm is like trying to eat an elephant,
you just have to keep focused and take it one 'byte' at a time.

22 Nov 2011, 12:16

DJ Mauretto

Joined: 14 Mar 2007
Posts: 464
Location: Rome,Italy

DJ Mauretto 22 Nov 2011, 13:35

I get This:

Code:

1111111111111111
1111111111111111
1111111100000000
0000000011111111
0000000010000001
0000000010000001
0000000010000001
1000000000000001
1000000000000001
1000000000000001
1000000000000001

Where is the bug ?

_________________
Nil Volentibus Arduum Razz

22 Nov 2011, 13:35

smiddy

Joined: 31 Oct 2004
Posts: 557

smiddy 22 Nov 2011, 18:54

DJ Mauretto wrote:

I get This:

Code:

1111111111111111
1111111111111111
1111111100000000
0000000011111111
0000000010000001
0000000010000001
0000000010000001
1000000000000001
1000000000000001
1000000000000001
1000000000000001

Where is the bug ?

I tried it also this morning and I received the same results as you, I just didn't have time to post.

22 Nov 2011, 18:54

bitshifter

Joined: 04 Dec 2007
Posts: 796
Location: Massachusetts, USA

bitshifter 22 Nov 2011, 21:12

Ok, i found the problem...
It turns out i was not thinking in 2's compliment (duh)
I have rewired my brain to remember this...
How stupid do i feel now?

22 Nov 2011, 21:12

ouadji

Joined: 24 Dec 2008
Posts: 1081
Location: Belgium

ouadji 22 Nov 2011, 21:40

Quote:

How stupid do i feel now?

relax, it can happen to anyone! Razz

http://board.flatassembler.net/topic.php?p=137196#137196
(last post)

_________________
I am not young enough to know everything (Oscar Wilde)-

22 Nov 2011, 21:40

shutdownall

Joined: 02 Apr 2010
Posts: 517
Location: Munich

shutdownall 22 Nov 2011, 22:20

ouadji wrote:

[color=green][size=14]
Quote:
How stupid do i feel now?
relax, it can happen to anyone!

But not to a bitshifter
He should know the difference between COMP and NEG why else did he use this nickname ? Razz

22 Nov 2011, 22:20

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