Question

I have a byte-sized number in register AL (8 bits), in 32-bit x86.

I need to exchange between bit 1 (the second from right) and bit 4 (the fifth from right) of the number in register AL.

For example

00010000B    input
00000010B    output

Answer 1

You may try this:

mov BL, AL
mov BH, AL

and BL, 2h   //empty all bits except first
and BH, 10h  //empty all bits except fourth

shl BL, 3    //move bit 1 to position of bit 4
shr BH, 3    //move bit 4 to position of bit 1

and AL, edh  //empty first and fourth bits
or AL, BL    //set bit 4
or AL, BH    //set bit 1

AL register contains the result. Also you may need data stored in register BX. If you do then prepend solution with

push BX

end append to the end

pop BX