compensateOverflow.hpp

#include <limits>
#include <assert.h>


template<class T>
long compensateOverflow(long near, T value)
{
  using namespace std;
	static const long delta = long(numeric_limits<T>::max()) - numeric_limits<T>::min() + 1;
	assert(delta%2 == 0);
	assert(delta > 10);
	assert(value < delta);
	assert(value > -delta);
	long rv = near - near % delta + value ;
	if (rv < near - delta / 2 )
		rv += delta;
	else if (rv > near + delta / 2)
		rv -= delta;
	assert(abs(rv - near) < delta / 2);
	return rv;
}