From: Daryle Walker (darylew_at_[hidden])
Date: 2001-03-16 09:03:04
The latest version (6) of "crc.zip" contains a prototype of finding a
built-in (unsigned) type that has exactly the desired number of bits. The
class template is in "crc.hpp" and is called "detail::exact_uint_t". It
should be a regular Boost class, maybe in <boost/integer.hpp>.
Here's a copy:
//=================================================================
#include <boost/integer.hpp>
#include <climits>
#include <cstddef>
//...
// Forward declarations
template < ::std::size_t Bits >
struct exact_uint_t;
template < >
struct exact_uint_t< CHAR_BIT >;
#if USHRT_MAX > UCHAR_MAX
template < >
struct exact_uint_t< CHAR_BIT * sizeof(unsigned short) >;
#endif
#if UINT_MAX > USHRT_MAX
template < >
struct exact_uint_t< CHAR_BIT * sizeof(unsigned int) >;
#endif
#if ULONG_MAX > UINT_MAX
template < >
struct exact_uint_t< CHAR_BIT * sizeof(unsigned long) >;
#endif
// Traits class for an unsigned type with exactly the amount
// of given bits (should go into <boost/integer.hpp> later)
template < >
struct exact_uint_t< CHAR_BIT >
{
typedef unsigned char exact;
typedef typename ::boost::int_fast_t<exact>::fast fast;
}; // boost::detail::exact_uint_t
#if USHRT_MAX > UCHAR_MAX
template < >
struct exact_uint_t< CHAR_BIT * sizeof(unsigned short) >
{
typedef unsigned short exact;
typedef typename ::boost::int_fast_t<exact>::fast fast;
}; // boost::detail::exact_uint_t
#endif
#if UINT_MAX > USHRT_MAX
template < >
struct exact_uint_t< CHAR_BIT * sizeof(unsigned int) >
{
typedef unsigned int exact;
typedef typename ::boost::int_fast_t<exact>::fast fast;
}; // boost::detail::exact_uint_t
#endif
#if ULONG_MAX > UINT_MAX
template < >
struct exact_uint_t< CHAR_BIT * sizeof(unsigned long) >
{
typedef unsigned long exact;
typedef typename ::boost::int_fast_t<exact>::fast fast;
}; // boost::detail::exact_uint_t
#endif
//=================================================================
-- Daryle Walker Mac, Internet, and Video Game Junkie darylew AT mac DOT com