407 lines
6.8 KiB
Plaintext
407 lines
6.8 KiB
Plaintext
;Load a file named in SI as a string ending in a null to the offset BX
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;and set AL to 0x0 if the load was succesful and 0x1 if there was an
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;error.
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loadf:
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;Store the initial registers in the stack
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push ax
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push bx
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push cx
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push dx
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push si
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push di
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;Store the current drive and offset
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mov word [.pointer], bx
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mov dl, byte [drive]
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mov byte [.drive], dl
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;Change the drive if needed
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;Check for a drive specification
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cmp byte [si + 0x1], ":"
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jne .start
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;Check which drive to change to
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cmp byte [si], "a"
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je .cha
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cmp byte [si], "A"
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je .cha
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cmp byte [si], "b"
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je .chb
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cmp byte [si], "B"
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je .chb
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cmp byte [si], "c"
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je .chc
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cmp byte [si], "C"
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je .chc
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cmp byte [si], "d"
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je .chd
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cmp byte [si], "D"
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je .chd
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;Set the carry flag and print an error message
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stc
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mov si, .driverrormsg
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mov ah, 0x2
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int 0x21
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jmp .done
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;Change
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.cha:
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mov dl, 0x0
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mov byte [.drive], dl
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jmp .drivechanged
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.chb:
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mov dl, 0x1
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mov byte [.drive], dl
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jmp .drivechanged
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.chc:
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mov dl, 0x2
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mov byte [.drive], dl
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jmp .drivechanged
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.chd:
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mov dl, 0x3
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mov byte [.drive], dl
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.drivechanged:
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add si, 0x2
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.start:
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;Set DI at .file and initialise it with spaces
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mov di, .file
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mov cx, 0xb
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mov al, 0x20
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rep stosb
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sub di, 0xb
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;Convert .file into FAT formatting
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;Initialise the length counter for the main part of the file name
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mov bl, 0x8
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;Convert the main part of the file name
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.nameloop:
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;Load a character
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lodsb
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;Check for a period
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cmp al, 0x2e
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je .initext
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;Check for everything else and convert to upper case
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call .checkconv
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jmp .nameloop
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;Convert the extension
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.initext:
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;Set DI and initialise the length counter for the extension
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mov bl, 0x3
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mov di, .file+0x8
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.extloop:
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;Load a character
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lodsb
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;Check for a period
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push ax
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cmp al, 0x2e
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je .error
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pop ax
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;Check for everything else and convert to upper case
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call .checkconv
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jmp .extloop
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;Set the carry flag and print an error message
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.error:
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pop ax
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stc
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mov si, .filerrormsg
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mov ah, 0x2
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int 0x21
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jmp .done
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;Find and load the file
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.load:
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pop ax
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;Load the disk description table
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;Set the source
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mov dl, [.drive]
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mov ch, 0x0
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mov dh, 0x0
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mov cl, 0x1
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;Set the destination
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mov si, buffer
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mov bx, si
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;Set the size
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mov al, 0x1
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;Load
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mov ah, 0x2
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int 0x13
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;Set the carry flag and print an error message
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jnc .storevalues
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mov si, .diskerrormsg
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mov ah, 0x2
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int 0x21
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jmp .done
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;Store the disk values used for the rest of the call
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.storevalues:
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mov ax, word [buffer + 0xb]
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mov word [.sectorsize], ax
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mov al, byte [buffer + 0xd]
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mov byte [.clustersize], al
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mov ax, word [buffer + 0xe]
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mov word [.bootsectors], ax
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mov al, byte [buffer + 0x10]
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mov byte [.fats], al
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mov ax, word [buffer + 0x11]
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mov word [.rootentries], ax
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mov ax, word [buffer + 0x16]
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mov word [.sectorsperfat], ax
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mov ax, word [buffer + 0x18]
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mov word [.sectorspertrack], ax
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mov ax, word [buffer + 0x1a]
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mov word [.sides], ax
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;Load the root
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;Set the source
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mov ah, 0x0
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mov al, [.fats]
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mul word [.sectorsperfat]
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add ax, [.bootsectors]
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push ax
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call .calcsource
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;Set the destination
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mov si, buffer
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mov bx, si
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;Set the size
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push dx
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mov ax, [.rootentries]
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mov dx, 0x20
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mul dx
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mov dx, 0x0
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div word [.sectorsize]
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pop dx
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push ax
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;Load
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mov ah, 0x2
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int 0x13
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;Search the root for the file entry
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;Set DI to the root
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mov di, buffer
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;Initialise the search loop
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mov cx, word [.rootentries]
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mov ax, 0x0
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.search:
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;Store CX in the stack
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push cx
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;Check for the file entry
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mov si, .file
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mov cx, 0xb
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rep cmpsb
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je .loadentry
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;Set DI to the next entry
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add ax, 0x20
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mov di, buffer
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add di, ax
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;Load CX from the stack
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pop cx
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loop .search
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;Set the carry flag and print an error message if the file is not found
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stc
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mov si, .filerrormsg
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mov ah, 0x2
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int 0x21
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jmp .clearstack
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;Load the file entry
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.loadentry:
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;Load CX from the stack
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pop cx
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;Store the first cluster
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mov ax, word [es:di+0xf]
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mov word [.cluster], ax
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;Set the source
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mov ax, 0x1
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call .calcsource
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;Set the destination
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mov di, buffer
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mov bx, di
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;Set the size
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mov ax, [.sectorsperfat]
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;Load
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mov ah, 0x2
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int 0x13
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;Load the file
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;Load a cluster
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.loadcluster:
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;Set the source
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pop cx
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pop bx
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mov ax, word [.cluster]
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sub ax, 0x2
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mul byte [.clustersize]
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add ax, bx
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add ax, cx
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push bx
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push cx
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;Set the destination
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mov bx, word [.pointer]
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;Load a sector
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mov ch, 0x0
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mov cl, byte [.clustersize]
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.loadsector:
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push cx
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call .calcsource
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;Set the size
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push ax
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mov al, 0x1
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;Load
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mov ah, 0x2
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int 0x13
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pop ax
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;Set the next sector
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add ax, 0x1
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add bx, word [.sectorsize]
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pop cx
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loop .loadsector
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;Calculate the next cluster
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mov ax, [.cluster]
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mov dx, 0x0
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mov bx, 0x3
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mul bx
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mov bx, 0x2
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div bx
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mov si, buffer
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add si, ax
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mov ax, word [ds:si]
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or dx, dx
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jz .even
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shr ax, 1
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shr ax, 1
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shr ax, 1
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shr ax, 1
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jmp .contcalc
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.even:
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and ax, 0xfff
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.contcalc:
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mov word [.cluster], ax
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cmp ax, 0xff8
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jge .clearcarry
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mov ax, [.sectorsize]
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mul word [.clustersize]
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add word [.pointer], ax
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jmp .loadcluster
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;Clear the carry flag if the load was succesful
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.clearcarry:
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clc
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;Clear the stack
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.clearstack:
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pop cx
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pop bx
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.done:
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;Load the initial registers from the stack
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pop di
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pop si
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pop dx
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pop cx
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pop bx
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pop ax
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;Set AL to 0x1 if there was an error and to 0x0 otherwise and return
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jc .setal
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mov al, 0x0
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iret
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.setal:
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mov al, 0x1
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iret
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;Data
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.drive db 0x0
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.sectorsize dw 0x0 ;bytes
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.clustersize db 0x0 ;sectors
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.bootsectors dw 0x0
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.fats db 0x0
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.rootentries dw 0x0
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.sectorsperfat dw 0x0
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.sectorspertrack dw 0x0
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.sides dw 0x0
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.file times 0xb db 0x20
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.cluster dw 0x0
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.pointer dw 0x0
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.driverrormsg db "Drive not found", 0x0
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.diskerrormsg db "Disk not found", 0x0
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.filerrormsg db "File not found", 0x0
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;Check the file name and convert to upper case
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.checkconv:
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;Check for the string end
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cmp al, 0x0
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je .load
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;Check for the length limit
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cmp bl, 0x0
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je .error
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;Check for invalid characters
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cmp al, 0x22
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je .error
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cmp al, 0x2a
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jl .contcheck1
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cmp al, 0x2c
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jg .contcheck1
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jmp .error
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.contcheck1:
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cmp al, 0x2f
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je .error
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cmp al, 0x3a
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jl .contcheck2
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cmp al, 0x3f
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jg .contcheck2
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jmp .error
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.contcheck2:
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cmp al, 0x5b
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jl .contcheck3
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cmp al, 0x5d
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jg .contcheck3
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jmp .error
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.contcheck3:
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cmp al, 0x7c
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je .error
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;Check for lower case
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cmp al, 0x61
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jl .storech
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cmp al, 0x7a
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jg .storech
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;Convert lower to upper case
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sub al, 0x20
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.storech:
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;Store the character
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stosb
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;Decrease the counter
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dec bl
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ret
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;Calculate the source arguments for loading data from the disk
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.calcsource:
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push ax
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push bx
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mov bx, ax
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mov dx, 0x0
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div word [.sectorspertrack]
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add dl, 0x1
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mov cl, dl
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mov ax, bx
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mov dx, 0x0
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div word [.sectorspertrack]
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mov dx, 0x0
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div word [.sides]
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mov dh, dl
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mov ch, al
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pop bx
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pop ax
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mov dl, byte [.drive]
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ret
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