; Project name	:	Assembly Library
; Description	:	Functions for memory access.

;
; XTIDE Universal BIOS and Associated Tools 
; Copyright (C) 2009-2010 by Tomi Tilli, 2011-2012 by XTIDE Universal BIOS Team.
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation; either version 2 of the License, or
; (at your option) any later version.
; 
; This program 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.		
; Visit http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
;		

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; OPTIMIZE_STRING_OPERATION
;	Parameters
;		%1:		Repeat instruction
;		%2:		String instruction without size (for example MOVS and not MOVSB or MOVSW)
;		CX:		Number of BYTEs to operate
;		DS:SI:	Ptr to source data
;		ES:DI:	Ptr to destination
;	Returns:
;		SI, DI:	Updated by number of bytes operated
;	Corrupts registers:
;		Nothing
;--------------------------------------------------------------------
%macro OPTIMIZE_STRING_OPERATION 2
	push	cx

	shr		cx, 1			; Operate with WORDs for performance
	jz	%%HandleRemainingByte
	%1		%2w
%%HandleRemainingByte:
	jnc		SHORT %%OperationCompleted
	%2b

ALIGN JUMP_ALIGN
%%OperationCompleted:
	pop		cx
%endmacro


;--------------------------------------------------------------------
; Memory_CopyCXbytesFromDSSItoESDI
;	Parameters
;		CX:		Number of bytes to copy
;		DS:SI:	Ptr to source data
;		ES:DI:	Ptr to destination buffer
;	Returns:
;		SI, DI:	Updated by number of bytes copied
;	Corrupts registers:
;		Nothing
;--------------------------------------------------------------------
%ifndef EXCLUDE_FROM_XTIDE_UNIVERSAL_BIOS
ALIGN JUMP_ALIGN
Memory_CopyCXbytesFromDSSItoESDI:
	OPTIMIZE_STRING_OPERATION rep, movs
	ret
%endif


;--------------------------------------------------------------------
; Memory_ZeroSSBPwithSizeInCX
;	Parameters
;		CX:		Number of bytes to zero
;		SS:BP:	Ptr to buffer to zero
;	Returns:
;		Nothing
;	Corrupts registers:
;		Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Memory_ZeroSSBPwithSizeInCX:
	push	es
	push	di
	push	ax
	call	Registers_CopySSBPtoESDI
	call	Memory_ZeroESDIwithSizeInCX
	pop		ax
	pop		di
	pop		es
	ret

;--------------------------------------------------------------------
; Memory_ZeroESDIwithSizeInCX
;	Parameters
;		CX:		Number of bytes to zero
;		ES:DI:	Ptr to destination buffer
;	Returns:
;		DI:		Updated by number of BYTEs stored
;	Corrupts registers:
;		AX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Memory_ZeroESDIwithSizeInCX:
	xor		ax, ax
	; Fall to Memory_StoreCXbytesFromAccumToESDI

;--------------------------------------------------------------------
; Memory_StoreCXbytesFromAccumToESDI
;	Parameters
;		AX:		Word to use to fill buffer
;		CX:		Number of BYTEs to store
;		ES:DI:	Ptr to destination buffer
;	Returns:
;		DI:		Updated by number of BYTEs stored
;	Corrupts registers:
;		Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Memory_StoreCXbytesFromAccumToESDI:
	OPTIMIZE_STRING_OPERATION rep, stos
	ret


;--------------------------------------------------------------------
; Memory_ReserveCXbytesFromStackToDSSI
;	Parameters
;		CX:		Number of bytes to reserve
;	Returns:
;		DS:SI:	Ptr to reserved buffer
;	Corrupts registers:
;		AX
;--------------------------------------------------------------------
%ifndef EXCLUDE_FROM_XTIDE_UNIVERSAL_BIOS
ALIGN JUMP_ALIGN
Memory_ReserveCXbytesFromStackToDSSI:
	pop		ax
	push	ss
	pop		ds
	sub		sp, cx
	mov		si, sp
	jmp		ax
%endif