Necessary cleanup in basics.lib

[sletz]

A lot of control like functions (which are producing various controls signals) are confusing. We should at least:

• define a set of standard front detections functions, like for instance:

// equal 1 for upfront, 0 otherwise
upfront(x) = x > x';    
  
// equal 1 for downfront, 0 otherwise        
downfront(x) =  x < x';  
      
// equal 1 for upfront or downfront, 0 otherwise
front(x) = x != x';     

// equal 0 for upfront, 1 otherwise              
inv_upfront(x) = x <= x';     

// equal 0 for downfront, 1 otherwise
inv_downfront(x) = x >= x';

// equal 0 for upfront or downfront, 1 otherwise 
inv_front(x) = x == x';        

• check all control like functions and see if they can use any of those front detections functions. For instance we currently have: latch(c,x) = x * s : + ~ *(1-s) with { s = ((c'<=0)&(c>0)); }; which could be rewritten as latch(c,x) = x * s : + ~ *(1-s) with { s = upfront(c); };