Header: <boost/math/common_factor_rt.hpp>

template < typename IntegerType >
IntegerType  boost::math::gcd( IntegerType const &a, IntegerType const &b );

template < typename ForwardIterator >
std::pair<typename std::iterator_traits<I>::value_type, I> gcd_range(I first, I last);

template < typename IntegerType >
IntegerType  boost::math::lcm( IntegerType const &a, IntegerType const &b );

The boost::math::gcd function template returns the greatest common (nonnegative) divisor of the two integers passed to it. boost::math::gcd_range is the iteration of the above gcd algorithm over a range, returning the greatest common divisor of all the elements. The algorithm terminates when the gcd reaches unity or the end of the range. Thus it also returns the iterator after the last element inspected because this may not be equal to the end of the range. The boost::math::lcm function template returns the least common (nonnegative) multiple of the two integers passed to it. The function templates are parameterized on the function arguments' IntegerType, which is also the return type. Internally, these function templates use an object of the corresponding version of the gcd_evaluator and lcm_evaluator class templates, respectively.