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Subject: Re: [Boost-users] [boost.numeric] Poor Performance of numeric_cast
From: Oswin Krause (Oswin.Krause_at_[hidden])
Date: 2012-10-16 03:55:25

Hi,

is this the total run time? can you show the code? Your run times are
the same as before. you should expect a runtime factor of 1000+ in the
end result - or the compiler was too smart.

On 2012-10-16 09:47, Tang Jiang Jun wrote:
> Hi,
>
> I adopted your suggestion to run the inner cast for 10000 * 10000
> times, and the result is same on my computer. I guess maybe the
> difference is caused by the architecture of our CPU, and my CPU is
> intel i3.
>
> Here is the result.
>
> Native Integer Cast: 2 nanoseconds
> 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: 15 nanoseconds
>
> On Tue, Oct 16, 2012 at 1:24 PM, Oswin Krause
> <Oswin.Krause_at_[hidden] [33]> wrote:
>
>> 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
>>> <brian.budge_at_[hidden] [15]
>>> [15]> wrote:
>>>
>>>> Unsure, but maybe you should put the try/catch outside of the
>>>> inner
>>>> loop?
>>>>
>>>> On Mon, Oct 15, 2012 at 8:50 PM, Tang Jiang Jun
>>>>
>>>> <tangjiangjun_at_[hidden] [1] [1]> wrote:
>>>> > Hi,
>>>> >
>>>> > I modify my code to make it can run in release mode without
>>>> unintended
>>>> > optimization, and now the performance is acceptable. However
>>>> there
>>>> > 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,
>>>> this
>>>> > overhead will impact the performance significantly .
>>>> >
>>>> > The following is the benchmark code after modification and
>>>> the
>>>> result run in
>>>> > my computer.
>>>> >
>>>> > CODE
>>>> > #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;
>>>> >
>>>> >
>>>> > 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
>>>>
>>>> > <Oswin.Krause_at_[hidden] [2] [2]> wrote:
>>>> >>
>>>> >> Hi,
>>>> >>
>>>> >> Never benchmark in debug mode. Moreover, never ever
>>>> benchmark
>>>> boost code
>>>> >> in debug mode.
>>>> >>
>>>> >>
>>>> >> On 2012-10-15 11:29, Tang Jiang Jun wrote:
>>>> >>>
>>>> >>> 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] [3] [3] [3]> 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
>>>> >>>>
>>>> >>>>
>>>> >>>> _______________________________________________
>>>> >>>> Boost-users mailing list
>>>> >>>> Boost-users_at_[hidden] [4] [4] [1]
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>>>> [5] [5]
>>>> [2]
>>>> >>>
>>>> >>>
>>>> >>>
>>>> >>>
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>>>> >>> [2] http://lists.boost.org/mailman/listinfo.cgi/boost-users
>>>> [7] [7]
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>>>> >>
>>>> >>
>>>> >> _______________________________________________
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>>>> >
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>>
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>
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