Chris@16: 
Chris@16: //  Copyright 2012 John Maddock. Distributed under the Boost
Chris@16: //  Software License, Version 1.0. (See accompanying file
Chris@16: //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_
Chris@16: 
Chris@16: #ifndef BOOST_MP_CPP_INT_CHECKED_HPP
Chris@16: #define BOOST_MP_CPP_INT_CHECKED_HPP
Chris@16: 
Chris@16: namespace boost{ namespace multiprecision{ namespace backends{ namespace detail{
Chris@16: 
Chris@16: //
Chris@16: // Simple routines for performing checked arithmetic with a builtin arithmetic type.
Chris@16: // Note that this is not a complete header, it must be included as part of boost/multiprecision/cpp_int.hpp.
Chris@16: //
Chris@16: 
Chris@16: inline void raise_overflow(std::string op)
Chris@16: {
Chris@16:    BOOST_THROW_EXCEPTION(std::overflow_error("overflow in " + op));
Chris@16: }
Chris@16: inline void raise_add_overflow()
Chris@16: {
Chris@16:    raise_overflow("addition");
Chris@16: }
Chris@16: inline void raise_subtract_overflow()
Chris@16: {
Chris@16:    BOOST_THROW_EXCEPTION(std::range_error("Subtraction resulted in a negative value, but the type is unsigned"));
Chris@16: }
Chris@16: inline void raise_mul_overflow()
Chris@16: {
Chris@16:    raise_overflow("multiplication");
Chris@16: }
Chris@16: inline void raise_div_overflow()
Chris@16: {
Chris@16:    raise_overflow("division");
Chris@16: }
Chris@16: 
Chris@16: template <class A>
Chris@16: inline A checked_add_imp(A a, A b, const mpl::true_&)
Chris@16: {
Chris@16:    if(a > 0)
Chris@16:    {
Chris@16:       if((b > 0) && ((integer_traits<A>::const_max - b) < a))
Chris@16:          raise_add_overflow();
Chris@16:    }
Chris@16:    else
Chris@16:    {
Chris@16:       if((b < 0) && ((integer_traits<A>::const_min - b) > a))
Chris@16:          raise_add_overflow();
Chris@16:    }
Chris@16:    return a + b;
Chris@16: }
Chris@16: template <class A>
Chris@16: inline A checked_add_imp(A a, A b, const mpl::false_&)
Chris@16: {
Chris@16:    if((integer_traits<A>::const_max - b) < a)
Chris@16:       raise_add_overflow();
Chris@16:    return a + b;
Chris@16: }
Chris@16: template <class A>
Chris@16: inline A checked_add(A a, A b, const mpl::int_<checked>&)
Chris@16: {
Chris@16:    return checked_add_imp(a, b, boost::is_signed<A>());
Chris@16: }
Chris@16: template <class A>
Chris@16: inline A checked_add(A a, A b, const mpl::int_<unchecked>&)
Chris@16: {
Chris@16:    return a + b;
Chris@16: }
Chris@16: 
Chris@16: template <class A>
Chris@16: inline A checked_subtract_imp(A a, A b, const mpl::true_&)
Chris@16: {
Chris@16:    if(a > 0)
Chris@16:    {
Chris@16:       if((b < 0) && ((integer_traits<A>::const_max + b) < a))
Chris@16:          raise_subtract_overflow();
Chris@16:    }
Chris@16:    else
Chris@16:    {
Chris@16:       if((b > 0) && ((integer_traits<A>::const_min + b) > a))
Chris@16:          raise_subtract_overflow();
Chris@16:    }
Chris@16:    return a - b;
Chris@16: }
Chris@16: template <class A>
Chris@16: inline A checked_subtract_imp(A a, A b, const mpl::false_&)
Chris@16: {
Chris@16:    if(a < b)
Chris@16:       raise_subtract_overflow();
Chris@16:    return a - b;
Chris@16: }
Chris@16: template <class A>
Chris@16: inline A checked_subtract(A a, A b, const mpl::int_<checked>&)
Chris@16: {
Chris@16:    return checked_subtract_imp(a, b, boost::is_signed<A>());
Chris@16: }
Chris@16: template <class A>
Chris@16: inline A checked_subtract(A a, A b, const mpl::int_<unchecked>&)
Chris@16: {
Chris@16:    return a - b;
Chris@16: }
Chris@16: 
Chris@16: template <class A>
Chris@16: inline A checked_multiply(A a, A b, const mpl::int_<checked>&)
Chris@16: {
Chris@16:    BOOST_MP_USING_ABS
Chris@16:    if(a && (integer_traits<A>::const_max / abs(a) < abs(b)))
Chris@16:       raise_mul_overflow();
Chris@16:    return a * b;
Chris@16: }
Chris@16: template <class A>
Chris@16: inline A checked_multiply(A a, A b, const mpl::int_<unchecked>&)
Chris@16: {
Chris@16:    return a * b;
Chris@16: }
Chris@16: 
Chris@16: template <class A>
Chris@16: inline A checked_divide(A a, A b, const mpl::int_<checked>&)
Chris@16: {
Chris@16:    if(b == 0)
Chris@16:       raise_div_overflow();
Chris@16:    return a / b;
Chris@16: }
Chris@16: template <class A>
Chris@16: inline A checked_divide(A a, A b, const mpl::int_<unchecked>&)
Chris@16: {
Chris@16:    return a / b;
Chris@16: }
Chris@16: 
Chris@16: template <class A>
Chris@16: inline A checked_left_shift(A a, unsigned long long shift, const mpl::int_<checked>&)
Chris@16: {
Chris@16:    if(a && shift)
Chris@16:    {
Chris@16:       if((shift > sizeof(A) * CHAR_BIT) || (a >> (sizeof(A) * CHAR_BIT - shift)))
Chris@16:          BOOST_THROW_EXCEPTION(std::overflow_error("Shift out of range"));
Chris@16:    }
Chris@16:    return a << shift;
Chris@16: }
Chris@16: template <class A>
Chris@16: inline A checked_left_shift(A a, unsigned long long shift, const mpl::int_<unchecked>&)
Chris@16: {
Chris@16:    return (shift >= sizeof(A) * CHAR_BIT) ? 0 : a << shift;
Chris@16: }
Chris@16: 
Chris@16: }}}} // namespaces
Chris@16: 
Chris@16: #endif
Chris@16: