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push bp
mov bp, sp ; needs to be &H8B, &HEC
pushf
mov al, 0
mov ah, 0x30
int 0x21
; Push actual version info onto stack
push ax
cmp bh, 0x00
jne notdrdos
; Check if it is DR_DOS lying about being PC_DOS
mov ax, 0x4452
int 0x21
jc notdrdos
; Mark drdos as 0xee
mov bh, 0xee
; clear the stack in a meaningless way
pop cx
; DrDos version, or something like it, is already in the ax reggy
jmp alldone
notdrdos:
; pop the actual version into ax now that we're done
; with drdos checks
pop ax
cmp al, 5
je five
; if al is still zero, it's dos 1
cmp al, 0
jne alldone
; Mark it as MS-DOS 1.0
mov al, 1
mov ah, 0
mov bh, 0xFF
jmp alldone
five:
; Store the OEM version
push bx
mov ax, 0x3306
int 0x21
; True version should have been in bx
push bx
pop ax
pop bx
alldone:
mov cl, 8
shr bx, cl
xor bh, bh
; second argument - OEM code in high byte
mov di, [bp]+6
mov [di], bx
; first argument - major (al) minor(ah) versions
mov di, [bp]+8
mov [di], ax
popf
pop bp
retf 4
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