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

16 Oct 2012

      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
 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
 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
...
Hi,
I modify my code to make it can run in release mode without
unintended
optimization, and now the performance is acceptable. However
...
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,
...
overhead will impact the performance significantly .
The following is the benchmark code after modification and
 wrote:
there
this
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:
...
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
...
...
>  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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