Re: BITON/TESTB RPG/FREE

PAPWORTH Paul wrote:

I have set up a bit of test code to better understand this and it works fine for the free form equivalents of TESTB and BITON. However in order to complete the cycle how could I setoff bit 2 ?

Simon's suggestions will work, but to help understand why I'll try to quickly explain how I came up with the "mask" value in the code sample earlier. Look at the definition of the operations:

AND OR
x | y | x AND y x | y | x AND y
------------------ ------------------
0 | 0 | 0 0 | 0 | 0
0 | 1 | 0 0 | 1 | 1
1 | 0 | 0 1 | 0 | 1
1 | 1 | 1 1 | 1 | 1


Notice that *1 AND y = y* and also *0 AND y = 0*. So if we have the mask=010, what are the possible results of %bitand(mask : value)? The first and third bits of the result will be 0, and the second bit will have whatever value the second bit in value has.

%bitand(010 : x1y) = 010 for any x,y
%bitand(010 : x0y) = 000 for any x,y


For setting bits, notice that *0 OR y = y* and and *1 OR y = 1*. Following similar logic, you can see that

%bitor(010 : x1y) = x1y for any x,y
%bitor(010 : x0y) = x1y for any x,y

HTH,
Adam