I've done some tests with gcc, which has an option to show the time
taken by each subprocess in the compilation sequence. Results and test
program are below. The file log2_impl.hpp contained either the trivial
implementation I've posted before, or Vesa's one, or a simple #include
"boost/static_log2.hpp". In the case of Vesa's implementation I
avoided inclusion of <climits> by simple replacing
sizeof(unsigned long) * CHAR_BIT / 2
with the literal 16.
Results are:
- trivial
$ g++ -I"...boost_1_29_0" -time log.cpp
# cc1plus 0.49 0.61
# as 0.04 0.09
# collect2 0.36 1.24
-vesa
$ g++ -I"...boost_1_29_0" -time log.cpp
# cc1plus 0.71 0.71
# as 0.05 0.07
# collect2 0.37 1.43
- boost::static_log2
$ g++ -I"...boost_1_29_0" -time log.cpp
# cc1plus 3.14 0.91
# as 0.05 0.07
# collect2 0.41 1.29
------ Test program
#include "log2_impl.hpp"
#include "boost/static_assert.hpp"
//#define log2 boost::static_log2
#define BOOST_INT_CONST_LOG2_TEST(val, result) \
BOOST_STATIC_ASSERT( log2<val>::value == result)
#ifdef BOOST_INT_CONST_LOG2_TEST_FOR_ZERO
enum { dummy = log2<0>::value }; // should give an error
#endif
int main()
{
// Test on 2**n and 2**n - 1
BOOST_INT_CONST_LOG2_TEST(1, 0);
BOOST_INT_CONST_LOG2_TEST(2, 1);
BOOST_INT_CONST_LOG2_TEST(3, 1);
BOOST_INT_CONST_LOG2_TEST(4, 2);
BOOST_INT_CONST_LOG2_TEST(7, 2);
BOOST_INT_CONST_LOG2_TEST(8, 3);
BOOST_INT_CONST_LOG2_TEST(15, 3);
BOOST_INT_CONST_LOG2_TEST(16, 4);
BOOST_INT_CONST_LOG2_TEST(31, 4);
BOOST_INT_CONST_LOG2_TEST(32, 5);
BOOST_INT_CONST_LOG2_TEST(63, 5);
BOOST_INT_CONST_LOG2_TEST(64, 6);
BOOST_INT_CONST_LOG2_TEST(127, 6);
BOOST_INT_CONST_LOG2_TEST(128, 7);
BOOST_INT_CONST_LOG2_TEST(255, 7);
BOOST_INT_CONST_LOG2_TEST(256, 8);
BOOST_INT_CONST_LOG2_TEST(511, 8);
BOOST_INT_CONST_LOG2_TEST(512, 9);
BOOST_INT_CONST_LOG2_TEST(1023, 9);
BOOST_INT_CONST_LOG2_TEST(1024, 10);
BOOST_INT_CONST_LOG2_TEST(2047, 10);
BOOST_INT_CONST_LOG2_TEST(2048, 11);
BOOST_INT_CONST_LOG2_TEST(4095, 11);
BOOST_INT_CONST_LOG2_TEST(4096, 12);
BOOST_INT_CONST_LOG2_TEST(8191, 12);
BOOST_INT_CONST_LOG2_TEST(8192, 13);
BOOST_INT_CONST_LOG2_TEST(16383, 13);
BOOST_INT_CONST_LOG2_TEST(16384, 14);
BOOST_INT_CONST_LOG2_TEST(32767, 14);
BOOST_INT_CONST_LOG2_TEST(32768, 15);
BOOST_INT_CONST_LOG2_TEST(65535, 15);
BOOST_INT_CONST_LOG2_TEST(65536, 16);
BOOST_INT_CONST_LOG2_TEST(131071, 16);
BOOST_INT_CONST_LOG2_TEST(131072, 17);
BOOST_INT_CONST_LOG2_TEST(262143, 17);
BOOST_INT_CONST_LOG2_TEST(262144, 18);
BOOST_INT_CONST_LOG2_TEST(524287, 18);
BOOST_INT_CONST_LOG2_TEST(524288, 19);
BOOST_INT_CONST_LOG2_TEST(1048575, 19);
BOOST_INT_CONST_LOG2_TEST(1048576, 20);
BOOST_INT_CONST_LOG2_TEST(2097151, 20);
BOOST_INT_CONST_LOG2_TEST(2097152, 21);
BOOST_INT_CONST_LOG2_TEST(4194303, 21);
BOOST_INT_CONST_LOG2_TEST(4194304, 22);
BOOST_INT_CONST_LOG2_TEST(8388607, 22);
BOOST_INT_CONST_LOG2_TEST(8388608, 23);
BOOST_INT_CONST_LOG2_TEST(16777215, 23);
BOOST_INT_CONST_LOG2_TEST(16777216, 24);
BOOST_INT_CONST_LOG2_TEST(33554431, 24);
BOOST_INT_CONST_LOG2_TEST(33554432, 25);
BOOST_INT_CONST_LOG2_TEST(67108863, 25);
BOOST_INT_CONST_LOG2_TEST(67108864, 26);
BOOST_INT_CONST_LOG2_TEST(134217727, 26);
BOOST_INT_CONST_LOG2_TEST(134217728, 27);
BOOST_INT_CONST_LOG2_TEST(268435455, 27);
BOOST_INT_CONST_LOG2_TEST(268435456, 28);
BOOST_INT_CONST_LOG2_TEST(536870911, 28);
BOOST_INT_CONST_LOG2_TEST(536870912, 29);
BOOST_INT_CONST_LOG2_TEST(1073741823, 29);
BOOST_INT_CONST_LOG2_TEST(1073741824, 30);
BOOST_INT_CONST_LOG2_TEST(2147483647, 30);
BOOST_INT_CONST_LOG2_TEST(2147483648u, 31);
BOOST_INT_CONST_LOG2_TEST(4294967295u, 31);
// Ok, now test again
BOOST_INT_CONST_LOG2_TEST(1, 0);
BOOST_INT_CONST_LOG2_TEST(2, 1);
BOOST_INT_CONST_LOG2_TEST(3, 1);
BOOST_INT_CONST_LOG2_TEST(4, 2);
BOOST_INT_CONST_LOG2_TEST(7, 2);
BOOST_INT_CONST_LOG2_TEST(8, 3);
BOOST_INT_CONST_LOG2_TEST(15, 3);
BOOST_INT_CONST_LOG2_TEST(16, 4);
BOOST_INT_CONST_LOG2_TEST(31, 4);
BOOST_INT_CONST_LOG2_TEST(32, 5);
BOOST_INT_CONST_LOG2_TEST(63, 5);
BOOST_INT_CONST_LOG2_TEST(64, 6);
BOOST_INT_CONST_LOG2_TEST(127, 6);
BOOST_INT_CONST_LOG2_TEST(128, 7);
BOOST_INT_CONST_LOG2_TEST(255, 7);
BOOST_INT_CONST_LOG2_TEST(256, 8);
BOOST_INT_CONST_LOG2_TEST(511, 8);
BOOST_INT_CONST_LOG2_TEST(512, 9);
BOOST_INT_CONST_LOG2_TEST(1023, 9);
BOOST_INT_CONST_LOG2_TEST(1024, 10);
BOOST_INT_CONST_LOG2_TEST(2047, 10);
BOOST_INT_CONST_LOG2_TEST(2048, 11);
BOOST_INT_CONST_LOG2_TEST(4095, 11);
BOOST_INT_CONST_LOG2_TEST(4096, 12);
BOOST_INT_CONST_LOG2_TEST(8191, 12);
BOOST_INT_CONST_LOG2_TEST(8192, 13);
BOOST_INT_CONST_LOG2_TEST(16383, 13);
BOOST_INT_CONST_LOG2_TEST(16384, 14);
BOOST_INT_CONST_LOG2_TEST(32767, 14);
BOOST_INT_CONST_LOG2_TEST(32768, 15);
BOOST_INT_CONST_LOG2_TEST(65535, 15);
BOOST_INT_CONST_LOG2_TEST(65536, 16);
BOOST_INT_CONST_LOG2_TEST(131071, 16);
BOOST_INT_CONST_LOG2_TEST(131072, 17);
BOOST_INT_CONST_LOG2_TEST(262143, 17);
BOOST_INT_CONST_LOG2_TEST(262144, 18);
BOOST_INT_CONST_LOG2_TEST(524287, 18);
BOOST_INT_CONST_LOG2_TEST(524288, 19);
BOOST_INT_CONST_LOG2_TEST(1048575, 19);
BOOST_INT_CONST_LOG2_TEST(1048576, 20);
BOOST_INT_CONST_LOG2_TEST(2097151, 20);
BOOST_INT_CONST_LOG2_TEST(2097152, 21);
BOOST_INT_CONST_LOG2_TEST(4194303, 21);
BOOST_INT_CONST_LOG2_TEST(4194304, 22);
BOOST_INT_CONST_LOG2_TEST(8388607, 22);
BOOST_INT_CONST_LOG2_TEST(8388608, 23);
BOOST_INT_CONST_LOG2_TEST(16777215, 23);
BOOST_INT_CONST_LOG2_TEST(16777216, 24);
BOOST_INT_CONST_LOG2_TEST(33554431, 24);
BOOST_INT_CONST_LOG2_TEST(33554432, 25);
BOOST_INT_CONST_LOG2_TEST(67108863, 25);
BOOST_INT_CONST_LOG2_TEST(67108864, 26);
BOOST_INT_CONST_LOG2_TEST(134217727, 26);
BOOST_INT_CONST_LOG2_TEST(134217728, 27);
BOOST_INT_CONST_LOG2_TEST(268435455, 27);
BOOST_INT_CONST_LOG2_TEST(268435456, 28);
BOOST_INT_CONST_LOG2_TEST(536870911, 28);
BOOST_INT_CONST_LOG2_TEST(536870912, 29);
BOOST_INT_CONST_LOG2_TEST(1073741823, 29);
BOOST_INT_CONST_LOG2_TEST(1073741824, 30);
BOOST_INT_CONST_LOG2_TEST(2147483647, 30);
BOOST_INT_CONST_LOG2_TEST(2147483648u, 31);
BOOST_INT_CONST_LOG2_TEST(4294967295u, 31);
}
---------------------
Genny.
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