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

Subject: Re: [Boost-users] [boost.numeric] Poor Performance of numeric_cast
From: Oswin Krause (Oswin.Krause_at_[hidden])
Date: 2012-10-15 04:30:24

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()
> {
> Â Â Â  const static int32_t COUNT = 1000000;
> Â Â Â  high_resolution_clock::time_point start;
>
>  Â Â Â  start = high_resolution_clock::now();
> Â Â Â  for( int32_t n = 0; n < COUNT; ++n )
> Â Â Â  {
> Â Â Â  Â Â Â  int32_t i32 = 123;
> Â Â Â  Â Â Â  int16_t i16 = i32;
> Â Â Â  }
> Â Â Â  cout << format("Native Integer Cast: %1%n") % ( (
> high_resolution_clock::now() - start ) / COUNT );
>
> Â Â Â  start = high_resolution_clock::now();
> Â Â Â  for( int32_t n = 0; n < COUNT; ++n )
> Â Â Â  {
> Â Â Â  Â Â Â  try
> Â Â Â  Â Â Â  {
> Â Â Â  Â Â Â  Â Â Â  int32_t i32 = 100;
> Â Â Â  Â Â Â  Â Â Â  int16_t i16 = numeric_cast< int16_t >( i32 );
>  Â Â Â  Â Â Â  }
> Â Â Â  Â Â Â  catch( const bad_numeric_cast& e )
> Â Â Â  Â Â Â  {
> Â Â Â  Â Â Â  Â Â Â  cout << e.what() << endl;
> Â Â Â  Â Â Â  }
> Â Â Â  }
> Â Â Â  cout << format("Boost Integer Cast: %1%n") % ( (
> high_resolution_clock::now() - start ) / COUNT );
>
> Â Â Â  start = high_resolution_clock::now();
> Â Â Â  for( int32_t n = 0; n < COUNT; ++n )
> Â Â Â  {
> Â Â Â  Â Â Â  float f = 100.0f;
> Â Â Â  Â Â Â  int32_t i = static_cast< int32_t >( f );
> Â Â Â  }
> Â Â Â  cout << format("Native Floating-Integer Cast: %1%n") % ( (
> high_resolution_clock::now() - start ) / COUNT );
>
> Â Â Â  start = high_resolution_clock::now();
> Â Â Â  for( int32_t n = 0; n < COUNT; ++n )
> Â Â Â  {
> Â Â Â  Â Â Â  try
> Â Â Â  Â Â Â  {
> Â Â Â  Â Â Â  Â Â Â  float f = 123.0f;
> Â Â Â  Â Â Â  Â Â Â  int32_t i = numeric_cast< int32_t >( f );
>  Â Â Â  Â Â Â  }
> Â Â Â  Â Â Â  catch( const bad_numeric_cast& e )
> Â Â Â  Â Â Â  {
> Â Â Â  Â Â Â  Â Â Â  cout << e.what() << endl;
> Â Â Â  Â Â Â  }
> Â Â Â  }
> Â Â Â  cout << format("Boost Floating-Integer Cast: %1%n") % ( (
> high_resolution_clock::now() - start ) / COUNT );
>
> Â Â Â  start = high_resolution_clock::now();
> Â Â Â  for( int32_t n = 0; n < COUNT; ++n )
> Â Â Â  {
> Â Â Â  Â Â Â  int32_t i = 132;
> Â Â Â  Â Â Â  float f = static_cast< float >( i );
> Â Â Â  }
> Â Â Â  cout << format("Native Integer-Floating Cast: %1%n") % ( (
> high_resolution_clock::now() - start ) / COUNT );
>
> Â Â Â  start = high_resolution_clock::now();
> Â Â Â  for( int32_t n = 0; n < COUNT; ++n )
> Â Â Â  {
> Â Â Â  Â Â Â  try
> Â Â Â  Â Â Â  {
> Â Â Â  Â Â Â  Â Â Â  int32_t i = 128;
> Â Â Â  Â Â Â  Â Â Â  float f = numeric_cast< float >( i );
>  Â Â Â  Â Â Â  }
> Â Â Â  Â Â Â  catch( const bad_numeric_cast& e )
> Â Â Â  Â Â Â  {
> Â Â Â  Â Â Â  Â Â Â  cout << e.what() << endl;
> Â Â Â  Â Â Â  }
> Â Â Â  }
> Â Â Â  cout << format("Boost Integer-Floating Cast: %1%n") % ( (
> high_resolution_clock::now() - start ) / COUNT );
>
> Â Â Â  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