Add skeleton of assembler
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com/a86.asm
325
com/a86.asm
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@ -1,88 +1,267 @@
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org 0x100
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org 0x100
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mov ax, 0x3D00
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mov dx, infile
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int 0x21
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jc err
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jmp init
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mov [fd], ax
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fcb1 equ 0x5C
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eof equ 0x1A
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stack equ 0x10 ; stack size
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call getline
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dumpax push ax
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push cx
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push dx
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mov dx, ax
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call dmpdx0
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mov al, 0x0A
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call dmpdx3
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mov al, 0x0D
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call dmpdx3
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pop dx
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pop cx
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pop ax
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ret
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dmpdx0 mov ah, 0xe
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mov cl, 4
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; this double-call is essentially a 4 times repeating loop
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call dmpdx1
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dmpdx1: call dmpdx2
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dmpdx2: ; grab highest nibble from dx
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mov al, dh
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; remove highest nibble from dx
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shl dx, cl
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; shift away second-highest nibble that we accidentally copied
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shr al, cl
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; map 0-9 to ascii codes for '0' to '9'
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add al, 0x30
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; if result is larger than '9', ...
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cmp al, 0x3a
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jl dmpdx3
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; ... add 7 so we continue at 'A'
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add al, 7
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dmpdx3: int 0x10
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ret
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mov dx, [line_length]
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call dumpdx
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free dw 0 ; free ram size
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lncnt dw 0 ; line count
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rdptr dw 0xFFFF ; infile blk ptr
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symbol dw 0 ; symbol of current line
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offset dw 0 ; byte offset in outfile
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len db 0 ; len for wrd (must be before it)
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wrd dw 0,0,0,0,0,0,0,0 ; 16 byte word buf
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mov si, line_buffer
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mov cx, [line_length]
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mov ah, 2
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l03: lodsb
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mov dl, al
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int 0x21
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loop l03
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getc mov bx, [rdptr]
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cmp bx, 0x80
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jc l01
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mov ah, 0x14
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mov dx, fcb1
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int 0x21
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cmp al, 1
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je l02
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mov bx, 0
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l01 mov al, [0x80+bx]
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cmp al, eof
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je l02
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cmp al, 0
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je l02
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cmp al, 0x0A
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jne l01b
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inc word [lncnt]
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l01b inc bx
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mov [rdptr], bx
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jmp l03
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l02 mov al, 0x1A
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l03 cmp al, eof
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ret
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end: ret
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;getc2 call peek
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; cmp al, eof
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; jne getc_
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; inc word [rdptr]
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;getc_ ret
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line_num: dw 1
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newlin mov dl, 0x0A
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mov ah, 2
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int 0x21
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mov dl, 0x0D
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int 0x21
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ret
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err: mov dx, ax
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error mov dl, [bx]
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mov ah, 2
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int 0x21
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inc bx
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cmp dl, 0x20
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jne error
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mov ax, [lncnt]
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call dumpax
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call newlin
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int 0x20
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dumpdx: ; setup bx and ah for int 10h call
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xor bx, bx
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mov ah, 0x0e
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mov cl, 4
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; this double-call is essentially a 4 times repeating loop
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call dmpdx1
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dmpdx1: call dmpdx2
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dmpdx2: ; grab highest nibble from dx
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mov al, dh
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; remove highest nibble from dx
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shl dx, cl
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; shift away second-highest nibble that we accidentally copied
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shr al, cl
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; map 0-9 to ascii codes for '0' to '9'
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add al, 0x30
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; if result is larger than '9', ...
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cmp al, 0x3a
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jl dmpdx3
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; ... add 7 so we continue at 'A'
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add al, 7
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dmpdx3: int 0x10
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ret
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e_eof db "EOF "
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e_dup db "DUPSYM "
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; read a character from the input file into DL
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getc: mov dl, 26
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push dx
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mov ah, 0x3f
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mov bx, [fd]
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mov cx, 1
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mov dx, sp
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int 0x21
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pop dx
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ret
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; scan word
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scawrd mov si, wrd
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l04 call getc
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; EOF is fatal
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mov bx, e_eof
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jz error
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; tab=end
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cmp al, 9
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je pad
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; space=end
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cmp al, 0x20
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je pad
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; if lbl full, continue eating
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cmp si, wrd+0x10
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jnc l04
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; insert
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mov [si], al
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inc si
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jmp l04
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; pad with spaces
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pad mov cx, si
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sub cx, wrd
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mov [len], cl
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cmp si, wrd+0x10
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jnc l06
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mov ah, 0x20
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xchg ah, [si]
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inc si
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cmp ah, 0x20
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jne pad
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l06 ret
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getline: mov word [line_length], 0
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mov di, line_buffer
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mov cx, line_buflen
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l02: push cx
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call getc
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pop cx
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mov al, dl
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cmp al, 0x0A
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je l01
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cmp al, 0x0D
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je l01
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cmp al, 0x1A
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je l01
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inc word [line_length]
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loop l02
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; print wrd
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dmpwrd mov si, wrd
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mov cx, 0x10
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mov ah, 2
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l05 mov dl, [si]
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cmp dl, 0x20
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je l07
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inc si
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int 0x21
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loop l05
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l07 call newlin
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ret
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l01: ret
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; create symbol table entry
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; name is read from [wrd]
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; offset is written to [symbol]
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symins cmp byte [wrd], 0x20
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je nosym
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mov bx, init ; walk ptr
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mov bp, [free]
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add bp, bx ; end addr
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jmp l09
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l08 add bx, 8
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l09 mov al, [bx]
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cmp al, 0
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je l10
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call symcmp
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jnz l08
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mov bx, e_dup
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jmp error
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; copy str to table
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l10 mov si, wrd
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mov di, bx
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movsw
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movsw
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movsw
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xor ax, ax
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stosw
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mov byte [bx+8], 0
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mov [symbol], bx
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ret
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infile: db "com/a86.asm", 0
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nosym xor ax, ax
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mov [symbol], ax
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ret
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line_buflen: equ 0x100
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line_length: dw 0 ; valid bytes in buffer
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line_prefix: times 16 db " "
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line_buffer: times line_buflen db 0
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; compares 6 bytes [bx] with [wrd]
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; bit 7 of each byte is ignored
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symcmp mov si, wrd
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xor ax, ax
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mov dx, [wrd]
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xor dx, [bx]
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or ax, dx
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mov dx, [wrd+2]
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xor dx, [bx+2]
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or ax, dx
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mov dx, [wrd+4]
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xor dx, [bx+4]
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or ax, dx
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test ax, 0x8F8F
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ret
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fd: dw 0
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; look up keyword in wrd
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; result is stored in bx
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lookup mov ch, 0
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mov bx, s_org
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l11 mov si, bx
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mov di, len ; wrd immediately follows
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mov cl, [bx]
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test cx, cx
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jz l13
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inc cl
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mov dx, cx
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rep cmpsb
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je l12
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add bx, dx
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jmp l11
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; found!
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l12 clc
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ret
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; give up
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l13 xor bx, bx
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stc
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ret
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s_org db 3, "org"
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s_equ db 3, "equ"
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db 0
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; clear symbol table
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main mov byte [init], 0
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; scan and create label
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mloop call scawrd
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call symins
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; scan instruction word
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call scawrd
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call lookup
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; special stuff
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cmp bx, s_org
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je iorg
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mov ax, bx
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call dumpax
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int 0x20
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; org pseudo instruction
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iorg mov ax, 0x5A5A
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call dumpax
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int 0x20
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align 16
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; stuff behind here gets overwritten
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; by symbol table and program data
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init mov ax, [6]
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mov dx, sp
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sub dx, stack
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cmp ax, dx
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jc il01
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mov ax, dx
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il01 sub ax, init
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shr ax, 1
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and ax, 0xFFF0
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mov [free], ax
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; open input file
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mov ah, 0x0F
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mov dx, fcb1
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int 0x21
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mov bx, e_op
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test al, al
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jnz error
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jmp main
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e_op db "NOFILE "
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