Test results for CRT-function 'sqrt' for different Floating Point Models

Test results for CRT-function 'sqrt' for different Floating Point Models

Intel C++ compiler supports four Floating Point Models:

Fast, Precise, Strict and Fast=2

and test results demonstrate how performance is affected when CRT-function sqrt is called ( results are in ASC order ):

[ Fast=2 (/fp:fast=2) [Intel C++] ]

32-bit Windows platform
CRT Sqrt - float - Calculating the Square Roots - 203 ticks
Last Result: 134217728.000^0.5 = 11585.236
CRT Sqrt - double - Calculating the Square Roots - 750 ticks
Last Result: 134217728.000^0.5 = 11585.237

[ Fast (/fp:fast) ]

32-bit Windows platform
CRT Sqrt - float - Calculating the Square Roots - 219 ticks
Last Result: 134217728.000^0.5 = 11585.236
CRT Sqrt - double - Calculating the Square Roots - 750 ticks
Last Result: 134217728.000^0.5 = 11585.237

[ Precise (/fp:precise) ]

32-bit Windows platform
CRT Sqrt - float - Calculating the Square Roots - 422 ticks
Last Result: 134217728.000^0.5 = 11585.237
CRT Sqrt - double - Calculating the Square Roots - 750 ticks
Last Result: 134217728.000^0.5 = 11585.237

[ Strict (/fp:strict) ]

32-bit Windows platform
CRT Sqrt - float - Calculating the Square Roots - 875 ticks
Last Result: 134217728.000^0.5 = 11585.237
CRT Sqrt - double - Calculating the Square Roots - 2969 ticks
Last Result: 134217728.000^0.5 = 11585.237

As you can see Fast=2 is the fastest Floating Point Model, and Strict is the slowest ( slower in 875 / 203 = ~4.3x ).

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Here are source codes of the test case:

#ifndef _WIN32_WINNT
#define _WIN32_WINNT 0x0501
#endif

#include "stdio.h"
#include "tchar.h"
#include "float.h"
#include "math.h"

#include "windows.h"

#ifdef _WIN32_PLATFORM
#define _WIN_PLATFORM _T("32-bit Windows platform")
#endif
#ifdef _WIN64_PLATFORM
#define _WIN_PLATFORM _T("64-bit Windows platform")
#endif

#define _USE_CRT_SQRT_FLOAT_
#define _USE_CRT_SQRT_DOUBLE_

int _tmain( void )
{
_tprintf( _T("%s\n"), _WIN_PLATFORM );

// Initializations
unsigned int uiTicksStart = 0U;
unsigned int uiControlWordx87 = 0U;

int iV = 0;
int iNumberOfIterations = 134217728; // 2^27
int iDummy = -1;

float fRes = 0.0f;
double dRes = 0.0L;

uiControlWordx87 = _control87( _PC_53, _MCW_PC );

// Sub-Test 1 - CRT sqrt - float
{
#ifdef _USE_CRT_SQRT_FLOAT_

_tprintf( _T("CRT Sqrt - float - Calculating the Square Roots") );
uiTicksStart = ::GetTickCount();
for( iV = 0; iV < iNumberOfIterations; iV++ )
{
iDummy = -1;

fRes = sqrt( ( float )iV );
}
_tprintf( _T(" - %ld ticks\n"), ( int )( ::GetTickCount() - uiTicksStart ) );
_tprintf( _T("\tLast Result: %.3f^0.5 = %.3f\n"), ( float )iV, fRes );

#endif
}

// Sub-Test 2 - CRT sqrt - double
{
#ifdef _USE_CRT_SQRT_DOUBLE_

_tprintf( _T("CRT Sqrt - double - Calculating the Square Roots") );
uiTicksStart = ::GetTickCount();
for( iV = 0; iV < iNumberOfIterations; iV++ )
{
iDummy = -1;

dRes = sqrt( ( double )iV );
}
_tprintf( _T(" - %ld ticks\n"), ( int )( ::GetTickCount() - uiTicksStart ) );
_tprintf( _T("\tLast Result: %.3f^0.5 = %.3f\n"), ( double )iV, dRes );

#endif
}

_tprintf( _T("Press ESC to Exit...\n") );
_gettch();

return ( int )0;
}

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