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

Hi, the results turnd out to have a high variance due to the low time usage. SInce just choosing higher count numbers already lead to an overflow, i hacked in the following loop: nanoseconds profile( PROFILE_FUNC _profileFunc, uint32_t _count ) { high_resolution_clock::time_point start = high_resolution_clock::now(); double summ = 0; for(std::size_t i = 0; i != 100000; ++i){ uint32_t sum = i; _profileFunc( _count, sum ); summ +=sum; } nanoseconds ns = ( high_resolution_clock::now() - start ) / _count; cout << summ << endl; return ns; } results: Native Integer Cast: 26729 nanoseconds Boost Integer Cast: 26449 nanoseconds Native Integer-Floating Cast: 105479 nanoseconds Boost Integer-Floating Cast: 105455 nanoseconds Native Floating-Integer Cast: 168933 nanoseconds Boost Floating-Integer Cast: 453505 nanoseconds so no overhead in Integer-Integer or Integer-Floating. But Floating-Integer has bad performance. On 2012-10-16 06:45, Tang Jiang Jun wrote:

I've already tried to remove all the try-catch blocks, but the overhead is still there. On the other side, when casting a number, it is general to use a dedicated try-catch block to protect it.

On Tue, Oct 16, 2012 at 12:08 PM, Brian Budge wrote:

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Unsure, but maybe you should put the try/catch outside of the inner loop?

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Hi,

I modify my code to make it can run in release mode without unintended optimization, and now the performance is acceptable. However

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definitely has some runtime overhead even no overflow happens, and the overhead takes extra time as much as the plain cast itself takes. I think this maybe should be mentioned in the numeric_cast document, because if the cast is the core step in an algorithms and is executed heavily,

On Mon, Oct 15, 2012 at 8:50 PM, Tang Jiang Jun wrote: there this

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overhead will impact the performance significantly .

The following is the benchmark code after modification and the result run in my computer.

CODE #include

#include #include #include #include <iostream>

using namespace std; using namespace boost; using namespace boost::numeric; using namespace boost::chrono;

typedef void (*PROFILE_FUNC)( uint32_t, uint32_t& );

nanoseconds profile( PROFILE_FUNC _profileFunc, uint32_t _count ) {     high_resolution_clock::time_point start = high_resolution_clock::now();

    uint32_t sum = 0;     _profileFunc( _count, sum );

    nanoseconds ns = ( high_resolution_clock::now() - start ) / _count;

    cout << sum << endl;

    return ns; }

void native_integer_cast( uint32_t _count, uint32_t& _sum ) {     for( uint64_t n = 0; n < _count; ++n )     {         _sum += static_cast< uint32_t >( n );     } }

void boost_integer_cast( uint32_t _count, uint32_t& _sum ) {     for( uint64_t n = 0; n < _count; ++n )     {         try         {             _sum += numeric_cast< uint32_t >( n );

        }         catch( const bad_numeric_cast& e )         {             cout << e.what() << endl;         }     } }

void native_itof_cast( uint32_t _count, uint32_t& _sum ) {     float fsum = 0.0f;

    for( uint32_t n = 0; n < _count; ++n )     {         fsum += static_cast< float >( n );     }

    _sum = static_cast< uint32_t >( fsum ); }

void boost_itof_cast( uint32_t _count, uint32_t& _sum ) {     float fsum = 0.0f;

    for( uint32_t n = 0; n < _count; ++n )     {         try         {             fsum += numeric_cast< float >( n );

        }         catch( const bad_numeric_cast& e )         {             cout << e.what() << endl;         }     }

    _sum = numeric_cast< uint32_t >( fsum ); }

void native_ftoi_cast( uint32_t _count, uint32_t& _sum ) {     for( float f = 0.0f; f < _count; f += 1.0f )     {         _sum += static_cast< uint32_t >( f );     } }

void boost_ftoi_cast( uint32_t _count, uint32_t& _sum ) {     for( float f = 0.0f; f < _count; f += 1.0f )     {         try         {             _sum += numeric_cast< uint32_t >( f );

        }         catch( const bad_numeric_cast& e )         {             cout << e.what() << endl;         }     } }

int main() {     const static int32_t COUNT = 10000;

    nanoseconds nsNativeIntegerCast = profile( native_integer_cast, COUNT );     nanoseconds nsBoostIntegerCast = profile( boost_integer_cast, COUNT );     nanoseconds nsNativeItofCast = profile( native_itof_cast, COUNT );     nanoseconds nsBoostItofCast = profile( boost_itof_cast, COUNT );     nanoseconds nsNativeFtoiCast = profile( native_ftoi_cast, COUNT );     nanoseconds nsBoostFtoiCast = profile( boost_ftoi_cast, COUNT );

    cout << "Native Integer Cast: " << nsNativeIntegerCast << endl;     cout << "Boost Integer Cast: " << nsBoostIntegerCast << endl;     cout << "Native Integer-Floating Cast: " << nsNativeItofCast << endl;     cout << "Boost Integer-Floating Cast: " << nsBoostItofCast << endl;     cout << "Native Floating-Integer Cast: " << nsNativeFtoiCast << endl;     cout << "Boost Floating-Integer Cast: " << nsBoostFtoiCast << endl;

    return 0; };

RESULT: Native Integer Cast: 1 nanosecond Boost Integer Cast: 4 nanoseconds Native Integer-Floating Cast: 3 nanoseconds Boost Integer-Floating Cast: 3 nanoseconds Native Floating-Integer Cast: 5 nanoseconds Boost Floating-Integer Cast: 14 nanoseconds

Regards, Tang

On Mon, Oct 15, 2012 at 6:43 PM, Oswin Krause wrote:

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Hi,

Never benchmark in debug mode. Moreover, never ever benchmark

boost code

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in debug mode.

On 2012-10-15 11:29, Tang Jiang Jun wrote:

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Hi Oswin,

Sorry, I forgot to mention that I compiled it as debug

configuration

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in order to prevent unintended optimization. Anyway, many thanks for reminding!

Tang

On Mon, Oct 15, 2012 at 4:30 PM, Oswin Krause wrote:

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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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