Re: BITON/TESTB RPG/FREE

[Adam Glauser <adamglauser@xxxxxxxxx>]

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