boolbv_onehot.cpp

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/*******************************************************************\
 
Module:
 
Author: Daniel Kroening, kroening@kroening.com
 
\*******************************************************************/
 
 
#include "boolbv.h"
 
literalt boolbvt::convert_onehot(const unary_exprt &expr)
{
  PRECONDITION(expr.id() == ID_onehot || expr.id() == ID_onehot0);
 
  bvt op=convert_bv(expr.op());
 
  literalt one_seen=const_literal(false);
  literalt more_than_one_seen=const_literal(false);
 
  for(bvt::const_iterator it=op.begin(); it!=op.end(); it++)
  {
    more_than_one_seen=
      prop.lor(more_than_one_seen, prop.land(*it, one_seen));
    one_seen=prop.lor(*it, one_seen);
  }
 
  if(expr.id() == ID_onehot)
  {
    // exactly one bit is set
    return prop.land(one_seen, !more_than_one_seen);
  }
  else
  {
    // onehot0: at most one bit is set
    return !more_than_one_seen;
  }
}