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Changed GCD for built-in integer types to use the binary-GCD algorithm

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[SVN r35850]
This commit is contained in:
Daryle Walker
2006-11-05 07:10:42 +00:00
committed by Peter Dimov
parent 56b287a590
commit 1f5f827a5e
2 changed files with 118 additions and 7 deletions
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100
include/boost/math/common_factor_rt.hpp
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@ -114,6 +114,62 @@ namespace detail
return ( result < zero ) ? -result : result;
}
// Greatest common divisor for unsigned binary integers
template < typename BuiltInUnsigned >
BuiltInUnsigned
gcd_binary
(
BuiltInUnsigned u,
BuiltInUnsigned v
)
{
if ( u && v )
{
// Shift out common factors of 2
unsigned shifts = 0;
while ( !(u & 1u) && !(v & 1u) )
{
++shifts;
u >>= 1;
v >>= 1;
}
// Start with the still-even one, if any
BuiltInUnsigned r[] = { u, v };
unsigned which = static_cast<bool>( u & 1u );
// Whittle down the values via their differences
do
{
// Remove factors of two from the even one
while ( !(r[ which ] & 1u) )
{
r[ which ] >>= 1;
}
// Replace the larger of the two with their difference
if ( r[!which] > r[which] )
{
which ^= 1u;
}
r[ which ] -= r[ !which ];
}
while ( r[which] );
// Shift-in the common factor of 2 to the residues' GCD
return r[ !which ] << shifts;
}
else
{
// At least one input is zero, return the other
// (adding since zero is the additive identity)
// or zero if both are zero.
return u + v;
}
}
// Least common multiple for rings (including unsigned integers)
template < typename RingType >
inline
@ -228,6 +284,50 @@ namespace detail
};
#endif
// Specialize for the built-in integers
#define BOOST_PRIVATE_GCD_UF( Ut ) \
template < > struct gcd_optimal_evaluator<Ut> \
{ Ut operator ()( Ut a, Ut b ) const { return gcd_binary( a, b ); } }
BOOST_PRIVATE_GCD_UF( unsigned char );
BOOST_PRIVATE_GCD_UF( unsigned short );
BOOST_PRIVATE_GCD_UF( unsigned );
BOOST_PRIVATE_GCD_UF( unsigned long );
#ifdef BOOST_HAS_LONG_LONG
BOOST_PRIVATE_GCD_UF( unsigned long long );
#endif
#ifdef BOOST_HAS_MS_INT64
BOOST_PRIVATE_GCD_UF( unsigned __int64 );
#endif
#undef BOOST_PRIVATE_GCD_UF
#define BOOST_PRIVATE_GCD_SF( St, Ut ) \
template < > struct gcd_optimal_evaluator<St> \
{ St operator ()( St a, St b ) const { Ut const a_abs = \
static_cast<Ut>( a < 0 ? -a : +a ), b_abs = static_cast<Ut>( \
b < 0 ? -b : +b ); return static_cast<St>( \
gcd_optimal_evaluator<Ut>()(a_abs, b_abs) ); } }
BOOST_PRIVATE_GCD_SF( signed char, unsigned char );
BOOST_PRIVATE_GCD_SF( short, unsigned short );
BOOST_PRIVATE_GCD_SF( int, unsigned );
BOOST_PRIVATE_GCD_SF( long, unsigned long );
BOOST_PRIVATE_GCD_SF( char, unsigned char ); // should work even if unsigned
#ifdef BOOST_HAS_LONG_LONG
BOOST_PRIVATE_GCD_SF( long long, unsigned long long );
#endif
#ifdef BOOST_HAS_MS_INT64
BOOST_PRIVATE_GCD_SF( __int64, unsigned __int64 );
#endif
#undef BOOST_PRIVATE_GCD_SF
#ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
#ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
template < typename T, bool IsSpecialized, bool IsSigned >