pcsx2/common/include/Utilities/win_memzero.h

/*  PCSX2 - PS2 Emulator for PCs
 *  Copyright (C) 2002-2010  PCSX2 Dev Team
 *
 *  PCSX2 is free software: you can redistribute it and/or modify it under the terms
 *  of the GNU Lesser General Public License as published by the Free Software Found-
 *  ation, either version 3 of the License, or (at your option) any later version.
 *
 *  PCSX2 is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 *  without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 *  PURPOSE.  See the GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along with PCSX2.
 *  If not, see <http://www.gnu.org/licenses/>.
 */

#pragma once

#ifdef _MSC_VER
#	pragma warning(disable:4063)	// case '1' is not a valid value for switch()
#endif

// These functions are meant for memset operations of constant length only.
// For dynamic length clears, use the C-compiler provided memset instead.

// MemZero Code Strategies:
//  I use a trick to help the MSVC compiler optimize it's asm code better.  The compiler
//  won't optimize local variables very well because it insists in storing them on the
//  stack and then loading them out of the stack when I use them from inline ASM, and
//  it won't allow me to use template parameters in inline asm code either.  But I can
//  assign the template parameters to enums, and then use the enums from asm code.
// Yeah, silly, but it works. :D  (air)

//  All methods defined in this header use template in combination with the aforementioned
//  enumerations to generate very efficient and compact inlined code.  These optimized
//  memsets work on the theory that most uses of memset involve static arrays and
//  structures, which are constant in size, thus allowing us to generate optimal compile-
//  time code for each use of the function.

// Use of CLD (Clear Direction Flag):
//  On Windows platforms the ABI declares that the direction flag should be cleared upon
//  entry of *any* function.  Therefore there is no need to have CLD prior to our use of
//  rep strosd here.

// Notes on XMM0's "storage" area (_xmm_backup):
// Unfortunately there's no way to guarantee alignment for this variable.  If I use the
// __declspec(aligned(16)) decorator, MSVC fails to inline the function since stack
// alignment requires prep work.  And for the same reason it's not possible to check the
// alignment of the stack at compile time, so I'm forced to use movups to store and
// retrieve xmm0.

// MSVC Template Issue:
//  MSVC treats int template parameters like macro insertions.  That is, if you have a
//  a template parameter in the form of "func<10-5>()", MSVC inserts 10-5 into the
//  templated function, causing order-of-operation problems (sigh).  The normal fix would
//  be to assign the template parameter to a static const int inside each function, but that
//  won't fly with the enums optimization.  So in order to fix the problem I define a macro
//  that encapsulates the template parameter inside parenthesis for us:

#define MZFbytes (_bytes)

// Code is only called in the init so no need to bother with ASM
template< u8 data, size_t bytes >
static __fi void memset_8( void *dest )
{
	memset(dest, data, bytes);
}

// This is unused on Windows.
template< u32 data, size_t MZFbytes >
static __fi void memset_32( void *dest )
{
	if( MZFbytes == 0 ) return;

	// Assertion: data length must be a multiple of 32 bits
	pxAssume( (MZFbytes & 0x3) == 0 );

	//u64 _xmm_backup[2];

	// This function only works on 32-bit alignments of data copied.
	// If the data length is not a factor of 32 bits, the C++ optimizing compiler will
	// probably just generate mysteriously broken code in Release builds. ;)

	pxAssume( (MZFbytes & 0x3) == 0 );

	enum
	{
		remdat = MZFbytes>>2,
		data32 = data
	};

	// macro to execute the x86/32 "stosd" copies.
	switch( remdat )
	{
		case 1:
			*(u32*)dest = data32;
		return;

		case 2:
			((u32*)dest)[0] = data32;
			((u32*)dest)[1] = data32;
		return;

		case 3:
			__asm
			{
				mov edi, dest;
				mov eax, data32;
				stosd;
				stosd;
				stosd;
			}
		return;

		case 4:
			__asm
			{
				mov edi, dest;
				mov eax, data32;
				stosd;
				stosd;
				stosd;
				stosd;
			}
		return;

		case 5:
			__asm
			{
				mov edi, dest;
				mov eax, data32;
				stosd;
				stosd;
				stosd;
				stosd;
				stosd;
			}
		return;

		default:
			__asm
			{
				mov ecx, remdat;
				mov edi, dest;
				mov eax, data32;
				rep stosd;
			}
		return
	}
}

// This method can clear any object-like entity -- which is anything that is not a pointer.
// Structures, static arrays, etc.  No need to include sizeof() crap, this does it automatically
// for you!
template< typename T >
static __fi void memzero( T& object )
{
	memset(&object, 0, sizeof(T));
}

// This method clears an object with the given 8 bit value.
template< u8 data, typename T >
static __fi void memset8( T& object )
{
	memset_8<data, sizeof(T)>( &object );
}

// This method clears an object with the given 32 bit value.
// This is also unused.
template< u32 data, typename T >
static __fi void memset32( T& object )
{
	memset_32<data, sizeof(T)>( &object );
}

#undef MZFbytes