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pool

Joined: 08 Jan 2007
Posts: 97

pool 13 Jan 2009, 05:02

Last edited by pool on 17 Mar 2013, 12:01; edited 1 time in total

13 Jan 2009, 05:02

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20337
Location: In your JS exploiting you and your system

revolution 13 Jan 2009, 05:08

JP
JNP
JPO
JPE

Check the Intel/AMD manual to see what flag value each tests for.

13 Jan 2009, 05:08

DJ Mauretto

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

DJ Mauretto 13 Jan 2009, 10:19

Hello,
The parity mean the number of bit that are set
Example:

Code:

mov al,1011b
test al,11b                     ; 1011 AND 11 = 11 ( 2 bit set = Parity even)
jp  @Parity


;Example 2:
mov al,101b
test al,1b                     ; 101 AND 1 = 1 ( 1 bit set = Parity odd )
jnp @No_Parity

Both jmp are execute Wink

_________________
Nil Volentibus Arduum Razz

13 Jan 2009, 10:19

pool

Joined: 08 Jan 2007
Posts: 97

pool 14 Jan 2009, 11:13

Last edited by pool on 17 Mar 2013, 12:02; edited 1 time in total

14 Jan 2009, 11:13

Grom PE

Joined: 13 Mar 2008
Posts: 114
Location: i@grompe.org.ru

Grom PE 16 Jan 2009, 03:33

I don't see jp/jnp in programs often.
Could anyone explain to me when it's useful?
It would be nice to see some uses in real projects, or as list of possibilities.

16 Jan 2009, 03:33

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 16 Jan 2009, 04:29

Grom PE, you may look here for a sample application. Wink

16 Jan 2009, 04:29

Grom PE

Joined: 13 Mar 2008
Posts: 114
Location: i@grompe.org.ru

Grom PE 16 Jan 2009, 06:09

baldr, that's interesting, but not useful enough - very specific case =)

16 Jan 2009, 06:09

sinsi

Joined: 10 Aug 2007
Posts: 789
Location: Adelaide

sinsi 16 Jan 2009, 06:16

http://coding.derkeiler.com/Archive/Assembler/comp.lang.asm.x86/2004-10/0310.html
Look at "next in thread" too. Interesting what you find out...

16 Jan 2009, 06:16

DJ Mauretto

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

DJ Mauretto 16 Jan 2009, 10:42

Quote:

I don't see jp/jnp in programs often.
Could anyone explain to me when it's useful?
It would be nice to see some uses in real projects, or as list of possibilities.

Read my signature Wink

_________________
Nil Volentibus Arduum Razz

16 Jan 2009, 10:42

Goplat

Joined: 15 Sep 2006
Posts: 181

Goplat 17 Jan 2009, 15:41

Suppose you're writing a NES emulator, and you need to classify a memory address into one of the four ranges (0000-1FFF = RAM, 2000-5FFF = memory mapped registers, 6000-7FFF = Save RAM, 8000-FFFF = ROM). Most people would use three comparisons to do this, but the flag-savvy programmer can do it with just one!

Code:

mov bx,[address]
test bh,0E0h
js rom_address             ; 8000-FFFF
jz ram_address           ; 0000-1FFF
jpe sram_address ; 6000-7FFF
jmp register_address     ; 2000-5FFF

17 Jan 2009, 15:41

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