;FAT12ReadFile(ULONG16 Base,ULONG16 Offset,ULONG16 OffsetFileName)

FAT12ReadFile:
.START:	
	push bp
	mov bp,sp
	push bp
	
	xor	ah, ah
	xor	dl, dl
	int	13h
	
	mov	word [wSectorNo], SectorNoOfRootDirectory
.LABEL_SEARCH_IN_ROOT_DIR_BEGIN:
	cmp	word [wRootDirSizeForLoop], 0	
	jz	.LABEL_NO_LOADERBIN	
	dec	word [wRootDirSizeForLoop]	
	mov	ax, [ss:bp+4]
	mov	es, ax
	mov	bx, [ss:bp+6]	
	mov	ax, [wSectorNo]	
	mov	cl, 1

	call	ReadSector
	
	mov	si, [ss:bp+8]
	mov	di, [ss:bp+6]
	cld
	mov	dx, 10h
.LABEL_SEARCH_FOR_LOADERBIN:
	cmp	dx, 0										
	jz	.LABEL_GOTO_NEXT_SECTOR_IN_ROOT_DIR	
	dec	dx										
	mov	cx, 11
.LABEL_CMP_FILENAME:
	cmp	cx, 0
	jz	.LABEL_FILENAME_FOUND
dec	cx
	lodsb			
	cmp	al, byte [es:di]
	jz	.LABEL_GO_ON
	jmp	.LABEL_DIFFERENT		
.LABEL_GO_ON:
	inc	di
	jmp	.LABEL_CMP_FILENAME	

.LABEL_DIFFERENT:
	and	di, 0FFE0h					
	add	di, 20h					
	mov	si, [ss:bp+8]				
	jmp	.LABEL_SEARCH_FOR_LOADERBIN;   

.LABEL_GOTO_NEXT_SECTOR_IN_ROOT_DIR:
	add	word [wSectorNo], 1
	jmp	.LABEL_SEARCH_IN_ROOT_DIR_BEGIN

.LABEL_NO_LOADERBIN:
	jmp	$

.LABEL_FILENAME_FOUND:			
	mov	ax, RootDirSectors
	and	di, 0FFE0h		
	add	di, 01Ah		
	mov	cx, word [es:di]
	push	cx		
	add	cx, ax
	add	cx, DeltaSectorNo	
	mov	ax, [ss:bp+4]
	mov	es, ax		
	mov	bx, [ss:bp+6]
	mov	ax, cx		

.LABEL_GOON_LOADING_FILE:
	mov	cl, 1
	call	ReadSector
	pop	ax	
	push word [ss:bp+4]
	call	GetFATEntry
	add sp,2
	cmp	ax, 0FFFh
	jz	.LABEL_FILE_LOADED
	push	ax			
	mov	dx, RootDirSectors
	add	ax, dx
	add	ax, DeltaSectorNo
	add	bx, [BPB_BytsPerSec]
	jmp	.LABEL_GOON_LOADING_FILE
	
.LABEL_FILE_LOADED:
	mov sp,[bp-2]
	pop bp
	ret
	
wRootDirSizeForLoop	dw	RootDirSectors	
wSectorNo		dw	0		
bOdd			db	0		

ReadSector:
	push bp
	mov	bp, sp
	sub	esp, 2		
	mov	byte [bp-2], cl
	push bx			
	mov	bl, [BPB_SecPerTrk]	
	div	bl			
	inc	ah			
	mov	cl, ah		
	mov	dh, al		
	shr	al, 1		
	mov	ch, al		
	and	dh, 1			
	pop	bx			
	mov	dl, [BS_DrvNum]		
.GoOnReading:
	mov	ah, 2		
	mov	al, byte [bp-2]	
	int	13h
	jc	.GoOnReading		

	add	sp, 2
	pop	bp

	ret

GetFATEntry:
	push	bp
	mov bp,sp
	push	es
	push	bx
	push	ax
	mov	ax, [ss:bp+4]
	sub	ax, 0100h	
	mov	es, ax
	pop	ax
	mov	byte [bOdd], 0
	mov	bx, 3
	mul	bx			
	mov	bx, 2
	div	bx			
	cmp	dx, 0
	jz	.LABEL_EVEN
	mov	byte [bOdd], 1
.LABEL_EVEN:
	xor	dx, dx			
	mov	bx, [BPB_BytsPerSec]
	div	bx
	push	dx
	mov	bx, 0 
	add	ax, SectorNoOfFAT1 
	mov	cl, 2
	call	ReadSector
			  
	pop	dx
	add	bx, dx
	mov	ax, [es:bx]
	cmp	byte [bOdd], 1
	jnz	.LABEL_EVEN_2
	shr	ax, 4
.LABEL_EVEN_2:
	and	ax, 0FFFh
.LABEL_GET_FAT_ENRY_OK:
	pop	bx
	pop	es
	pop bp
	ret