float_cast.h

/*
** Copyright (C) 2001 Erik de Castro Lopo <erikd AT mega-nerd DOT com>
**
** Permission to use, copy, modify, distribute, and sell this file for any
** purpose is hereby granted without fee, provided that the above copyright
** and this permission notice appear in all copies.  No representations are
** made about the suitability of this software for any purpose.  It is
** provided "as is" without express or implied warranty.
*/

/* Version 1.1 */


/*============================================================================
**	On Intel Pentium processors (especially PIII and probably P4), converting
**	from float to int is very slow. To meet the C specs, the code produced by
**	most C compilers targeting Pentium needs to change the FPU rounding mode
**	before the float to int conversion is performed.
**
**	Changing the FPU rounding mode causes the FPU pipeline to be flushed. It
**	is this flushing of the pipeline which is so slow.
**
**	Fortunately the ISO C99 specifications define the functions lrint, lrintf,
**	llrint and llrintf which fix this problem as a side effect.
**
**	On Unix-like systems, the configure process should have detected the
**	presence of these functions. If they weren't found we have to replace them
**	here with a standard C cast.
*/

/*
**	The C99 prototypes for lrint and lrintf are as follows:
**
**		long int lrintf (float x) ;
**		long int lrint  (double x) ;
*/



/*	The presence of the required functions are detected during the configure
**	process and the values HAVE_LRINT and HAVE_LRINTF are set accordingly in
**	the config.h file.
*/
#if (defined (WIN32) || defined (_WIN32)) && defined(_MSC_VER) && defined(_M_IX86)
	// As of Visual Studio 2019 16.9, these functions have been made intrinsic and the build
	// will fail. Unfortunately, the intrinsic versions run a LOT slower than the ones
   // below, so force the compiler to use ours instead.
	#pragma function( lrint, lrintf )

   // Including math.h allows us to use the inline assembler versions without
   // producing errors in newer Visual Studio versions.
   // Without the include, we get different linkage error messages.
   // Without the inline assembler versions, these functions are VERY slow.
   // I also see that the include was part of the original source for this file:
   //    http://www.mega-nerd.com/FPcast/
   
   #include <math.h>

   /*	Win32 doesn't seem to have these functions.
	**	Therefore implement inline versions of these functions here.
	*/
	__inline long int
	lrint (double flt)
	{	int intgr;

		_asm
		{	fld flt
			fistp intgr
			} ;

		return intgr ;
	}

	__inline long int
	lrintf (float flt)
	{	int intgr;

		_asm
		{	fld flt
			fistp intgr
			} ;

		return intgr ;
	}

	__inline long long int
	llrint (double flt)
	{	long long int intgr;

		_asm
		{	fld flt
			fistp intgr
			} ;

		return intgr ;
	}

	__inline long long int
	llrintf (float flt)
	{	long long int intgr;

		_asm
		{	fld flt
			fistp intgr
			} ;

		return intgr ;
	}
#elif (defined (WIN32) || defined (_WIN32)) && defined(_M_3X64)

	#include <math.h>
	#include <immintrin.h>

	__inline long int
	lrintf (float flt)
	{
		return _mm_cvt_ss2si(_mm_set_ss(flt));
	}

#elif (HAVE_LRINT && HAVE_LRINTF)

	/*	These defines enable functionality introduced with the 1999 ISO C
	**	standard. They must be defined before the inclusion of math.h to
	**	engage them. If optimisation is enabled, these functions will be
	**	inlined. With optimisation switched off, you have to link in the
	**	maths library using -lm.
	*/

	#define	_ISOC9X_SOURCE 1
	#define  _ISOC99_SOURCE 1

	#define	__USE_ISOC9X   1
	#define	__USE_ISOC99   1

	#include	<math.h>
#else

   /* dmazzoni: modified these to do a proper rounding, even though
    * it's slower.  Correctness and consistency is more important
    * than speed, especially since lrint/lrintf are certainly not
    * available everywhere.
    *
    * MM: Now uses internal math.h rint() function
    */

   #include	<math.h>

   #define	lrint(dbl)		((int)rint(dbl))
	#define	lrintf(flt)		((int)rint(flt))

#endif