Check if a reg have this numbers...

[shekel]

In AL i have a number between 0x01 and 0x0F inclusives .. so i want check if this number is 02, 03, 06, 07, 0A, 0B, 0E, 0F...

I know that all this number have something in comun and others not.

the bit in bold is always 1

2 = 00000010
3 = 00000011

How can check that this bit is 1??

Sorry by my english.. is not my native language

[dedndave]

Code Select Expand

test al,2
will set or clear the ZERO flag according to the value
you may then use JZ or JNZ to branch

or

Code Select Expand

bt eax,1
will set the CARRY flag if bit 1 is set
you may then use JC or JNC to branch
or, shift the CF into a register, perhaps

[dedndave]

those tests will tell you whether or not bit 1 is set
but, that's not the same for all values from 01h to 0Fh

Code Select Expand

01 0001
02 0010
03 0011
04 0100
05 0101
06 0110
07 0111
08 1000
09 1001
0A 1010
0B 1011
0C 1100
0D 1101
0E 1110
0F 1111

this code will work...

Code Select Expand

    or      al,al
    jz      not_1_to_F

    test    al,0F0h
    jz      not_1_to_F
is_1_to_F:

there are other ways to do it, too
if you want really fast, a look-up table might work

[Gunther]

if you want really fast, a look-up table might work

Yes that's the way to go. Another option could be an OR bitmask.

Gunther

[shekel]

now this is my code...

Code Select Expand

ror al, 4               ; because i have 60 and not 06
and al,0010b                 ;
jnz section_executable  ; jump if is xx1x


Is that good?

[nidud]

deleted

[Corso]

Hi,

if you only want to check any single bit (or half byte) then you can also do this.Sometimes I need it too to read any PE Chars out.

Code Select Expand

mov eax,0x11111111 ; something in eax
pushad
mov dl,al
and dl,0F0 ; bitwise
shr dl, 4 ; right shift
cmp dl, 1
je @ONE
popad
@NOT_ONE:
nop
@ONE:
    popad
    nop
Just a quick example.

greetz