/******************************************************************/
/* fpunitControl.cpp                                              */
/* -----------------------                                        */
/*                                                                */
/* This file contains the following functions, which may help to  */
/*     increase the performance of your floating-point intensive  */
/*     programs.  Note that functions documented in the comment   */
/*     have been tested under VisualStudio.NET 2003 and gcc 3.4.4 */
/*     (under Cygwin) on a 32-bit version of Windows.  The usage  */
/*     under 64-bit environments is not guaranteed to work.       */
/*                                                                */
/* void UseSinglePrecisionCalculations( void );                   */
/*     * Switches the CPU's FP unit to use only single-precision  */
/*       calculation. (Using 'float' instead of 'double' only     */
/*       uses smaller variable to store the results, but still    */
/*       performs calculations with double precision, by default) */
/*                                                                */
/* void UseDoublePrecisionCalculations( void );                   */
/*     * Switches the CPU's FP unit to use double-precision       */
/*       for calculations.                                        */
/*                                                                */
/* Chris Wyman (1/10/2007)                                        */
/******************************************************************/
/*                                                                */
/* For more info: http://www.stereopsis.com/FPU.html              */
/*           and: http://www.geisswerks.com/ryan/FAQS/fpu.html    */
/*                                                                */
/******************************************************************/



// We use some VisualStudio-specific controls to simplify coding 
//     under Windows.
#if defined(WIN32)
#include <float.h>
#else
// Masks for the floating point control word, these are used in
//     non-Windows versions of the code.
#define __FPU_CW_PREC_MASK__        (0x0300)
#define __FPU_CW_PREC_SINGLE__      (0x0000)
#define __FPU_CW_PREC_DOUBLE__      (0x0200)
#define __FPU_CW_PREC_EXTENDED__    (0x0300)
#endif


// Switch to single-precision floating point computations.
void UseSinglePrecisionCalculations( void )
{
#if defined(WIN32)
	_controlfp(_PC_24, MCW_PC);
#else
	// Get a copy of the current FP state
	unsigned int control = 0;
	__asm__ __volatile__ ( "fnstcw %0" : "=m" (control) );

	// Check if single precision is already enabled
	if (control & __FPU_CW_PREC_MASK__)              
    {
		// Nope... Setup single precision mode.
		control &= ~__FPU_CW_PREC_MASK__;

		// Write the new state back out.
		__asm__ __volatile__ ("fldcw %0" : : "m" (control));
	}
#endif
}


// Switch to double-precision floating point computations.
void UseDoublePrecisionCalculations( void )
{
#if defined(WIN32)
	_controlfp(_PC_53, MCW_PC);
#else
	// Get a copy of the current FP state
	unsigned int control = 0;
	__asm__ __volatile__ ( "fnstcw %0" : "=m" (control) );

	// Check if double precision is already enabled
	if (!(control & __FPU_CW_PREC_DOUBLE__))              
    {
		// Nope... Setup double precision mode.
		control &= ~__FPU_CW_PREC_MASK__;    // Clear out any the register's precision bits
		control |= __FPU_CW_PREC_DOUBLE__;   // Or in the new (double) value.

		// Write the new state back out.
		__asm__ __volatile__ ("fldcw %0" : : "m" (control));
	}
#endif
}