[Coco] replicating bitwise operators in BASIC

[Johann Klasek]

On Fri, Sep 09, 2016 at 02:23:47PM -0500, Dave Philipsen wrote:
> The less complicated way of doing this on a CoCo (since it has an 'OR' 
> operator) would be:
> 
> 10 A = 0: B = 0: GOSUB 100
> 20 A = 1: B = 0: GOSUB 100
> 30 A = 0: B = 1: GOSUB 100
> 40 A = 1: B = 1: GOSUB 100
> 90 STOP
> 100 Q = NOT ( A AND B ) AND ( A OR B )
> 110 PRINT "A = ";A;" B = ";B;" Q = ";Q
> 120 RETURN

line 100 is equivalent to
100 Q = ( A OR B ) - ( A AND B ) 
which is slightly faster, but not very understandable why ... AND NOT(...)
could be replaced by ...-(...) in this special case.

( A OR B ) table
   |B 
   |0 1 
---+---
A 0|0 1
  1|1 1

(A AND B) table
   |B
   |0 1
---+--- 
A 0|0 0
  1|0 1

a simple subtraction of the tables removes the 1 for A=1, B=1 in the (A OR
B) table resulting the XOR table.
   |B 
   |0 1 
---+---
A 0|0 1
  1|1 0