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Implemented integer_log2 in terms of countl_zero from Boost.Core.

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This allows to use compiler intrinsics and specialized hardware
instructions to compute log2, which results in better performance.

Also, added tests for the generic implementation using Boost.Multiprecision
integers.

Closes https://github.com/boostorg/integer/issues/31.
This commit is contained in:
Andrey Semashev
2022-01-16 15:20:37 +03:00
parent c6564a2d2b
commit bc9b0e6177
2 changed files with 88 additions and 33 deletions
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26
test/integer_log2_test.cpp
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@ -15,6 +15,11 @@
#include <iostream>
#include "multiprecision_config.hpp"
#if !defined(DISABLE_MP_TESTS)
#include <boost/multiprecision/cpp_int.hpp>
#endif
// Macros to compact code
#define PRIVATE_LB_TEST( v, e ) BOOST_TEST( ::boost::integer_log2((v)) == e )
@ -29,7 +34,6 @@
#define PRIVATE_LB_0_TEST PRIVATE_PRINT_LB( 0 )
#endif
// Main testing function
int main()
{
@ -159,5 +163,25 @@ int main()
PRIVATE_LB_TEST( ~boost::uint128_type(0u), 127 );
#endif
#if !defined(DISABLE_MP_TESTS)
PRIVATE_LB_TEST( boost::multiprecision::cpp_int(1), 0 );
PRIVATE_LB_TEST( boost::multiprecision::cpp_int(2), 1 );
PRIVATE_LB_TEST( boost::multiprecision::cpp_int(3), 1 );
PRIVATE_LB_TEST( boost::multiprecision::cpp_int(65535), 15 );
PRIVATE_LB_TEST( boost::multiprecision::cpp_int(65536), 16 );
PRIVATE_LB_TEST( boost::multiprecision::int1024_t(1), 0 );
PRIVATE_LB_TEST( boost::multiprecision::int1024_t(2), 1 );
PRIVATE_LB_TEST( boost::multiprecision::int1024_t(3), 1 );
PRIVATE_LB_TEST( boost::multiprecision::int1024_t(65535), 15 );
PRIVATE_LB_TEST( boost::multiprecision::int1024_t(65536), 16 );
PRIVATE_LB_TEST( boost::multiprecision::uint1024_t(1), 0 );
PRIVATE_LB_TEST( boost::multiprecision::uint1024_t(2), 1 );
PRIVATE_LB_TEST( boost::multiprecision::uint1024_t(3), 1 );
PRIVATE_LB_TEST( boost::multiprecision::uint1024_t(65535), 15 );
PRIVATE_LB_TEST( boost::multiprecision::uint1024_t(65536), 16 );
#endif
return boost::report_errors();
}