Re: [Boost-users] [boost.numeric] Poor Performance of numeric_cast

15 Oct 2012

      Hi Oswin,

Sorry, I forgot to mention that I compiled it as debug configuration in
order to prevent unintended optimization.
Anyway, many thanks for reminding!

Tang

On Mon, Oct 15, 2012 at 4:30 PM, Oswin Krause <
Oswin.Krause@ruhr-uni-bochum.de> wrote:
...
Hi,
Your complete loop got optimized away in the native test cases. Because of
the try/catch block the compiler couldn't do this in the other cases. So
you are benchmarking nothing vs somthing.
Greetings,
Oswin
On 2012-10-15 10:16, Tang Jiang Jun wrote:
...
Hi,
I have run a performance testing for numeric_cast recently, and found
that the result was really unexpected bad, although the document
mentioned that it will be no overhead if overflows don't happen.
Could somebody please help me to verify this testing? If this is true,
I doubt whether I should use numeric_cast in the production code.
Here is my testing code and result.
#include 
#include 
#include 
 #include 
#include <iostream>
using namespace std;
using namespace boost;
using namespace boost::numeric;
using namespace boost::chrono;
int main()
{
    const static int32_t COUNT = 1000000;
    high_resolution_clock::time_**point start;
start = high_resolution_clock::now();
    for( int32_t n = 0; n < COUNT; ++n )
    {
        int32_t i32 = 123;
        int16_t i16 = i32;
    }
    cout << format("Native Integer Cast: %1%n") % ( (
high_resolution_clock::now() - start ) / COUNT );
start = high_resolution_clock::now();
    for( int32_t n = 0; n < COUNT; ++n )
    {
        try
        {
            int32_t i32 = 100;
            int16_t i16 = numeric_cast< int16_t >( i32 );
         }
        catch( const bad_numeric_cast& e )
        {
            cout << e.what() << endl;
        }
    }
    cout << format("Boost Integer Cast: %1%n") % ( (
high_resolution_clock::now() - start ) / COUNT );
start = high_resolution_clock::now();
    for( int32_t n = 0; n < COUNT; ++n )
    {
        float f = 100.0f;
        int32_t i = static_cast< int32_t >( f );
    }
    cout << format("Native Floating-Integer Cast: %1%n") % ( (
high_resolution_clock::now() - start ) / COUNT );
start = high_resolution_clock::now();
    for( int32_t n = 0; n < COUNT; ++n )
    {
        try
        {
            float f = 123.0f;
            int32_t i = numeric_cast< int32_t >( f );
         }
        catch( const bad_numeric_cast& e )
        {
            cout << e.what() << endl;
        }
    }
    cout << format("Boost Floating-Integer Cast: %1%n") % ( (
high_resolution_clock::now() - start ) / COUNT );
start = high_resolution_clock::now();
    for( int32_t n = 0; n < COUNT; ++n )
    {
        int32_t i = 132;
        float f = static_cast< float >( i );
    }
    cout << format("Native Integer-Floating Cast: %1%n") % ( (
high_resolution_clock::now() - start ) / COUNT );
start = high_resolution_clock::now();
    for( int32_t n = 0; n < COUNT; ++n )
    {
        try
        {
            int32_t i = 128;
            float f = numeric_cast< float >( i );
         }
        catch( const bad_numeric_cast& e )
        {
            cout << e.what() << endl;
        }
    }
    cout << format("Boost Integer-Floating Cast: %1%n") % ( (
high_resolution_clock::now() - start ) / COUNT );
return 0;
};
Result:
Native Integer Cast: 3 nanoseconds
Boost Integer Cast: 311 nanoseconds
Native Floating-Integer Cast: 4 nanoseconds
 Boost Floating-Integer Cast: 430 nanoseconds
Native Integer-Floating Cast: 2 nanoseconds
Boost Integer-Floating Cast: 106 nanoseconds
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