Swap bytes without temporary variable ?

[Buzby]

Hi All,

Somewhere on the web, and in this forum I think, I've seen a method for swapping two bytes without using a 3rd temporary byte.

Plenty searching, but I still can't find it !.

Please help.

 

[benryves]

I believe you're referring to the XOR swap?

 

[tarzan]

From manual2:

swap
Syntax:
SWAP variable1, variable2
Function:
Swap the values between two variables.
Information:
The swap command simply exchanges values between two variables.
Example:
b1 = 5
b2 = 10
main:
swap b1,b2
debug
pause 1000
goto main

 

[kewakl]

Swap works on 20X2, 28X1, 28X2, 40X1 and 40X2 as per manual 2.

 

[inglewoodpete]

For the other chips, do the following:

Poke <RAM>, bx 
bx = by
Peek <RAM>, by

 

[Buzby]

Hi All,

Poke and peek looks the way I'll go. ( Can't use 'swap' because the PICAXE is not an X part. )

The XOR method looks like it may be another version of the one I was looking for, which I have just found in the forum !.

In post #15 of this thread :

http://www.picaxeforum.co.uk/showthread.php?t=5785

Womai shows how to do it it with maths

b0 = x
b1 = y

' now swap
b0 = b0 + b1 ' variables hold (x+y) and y
b1 = b0 - b1 ' variables hold (x+y) and x
b0 = b0 - b1 ' variables hold y and x

Try it and see the magic at work

Thanks,

Buzby

 

[kewakl]

Buzby, make sure that you understand another piece of info from that post
...

provided b0+b1 is no larger than 255

...