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

Subject: Re: [Boost-users] [boost.numeric] Poor Performance of numeric_cast
From: Tang Jiang Jun (tangjiangjun_at_[hidden])
Date: 2012-10-15 05:29:18

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_at_[hidden]> 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 <boost/numeric/conversion/**cast.hpp>
>> #include <boost/format.hpp>
>> #include <boost/cstdint.hpp>
>>  #include <boost/chrono.hpp>
>> #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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