87 lines
917 B
NASM
87 lines
917 B
NASM
cpu 8086
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org 0x3000
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xor dx, dx
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cmp byte [si], 0
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jne atoi
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mov ah, 2
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mov si, overflow_msg
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int 0x21
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int 0x20
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atoi:
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lodsb
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cmp al, 0
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je .end
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cmp al, '0'
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jl .notdigit
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cmp al, '9'
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jg .notdigit
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xor ah, ah
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sub al, '0'
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mov cx, ax
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mov ax, dx
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mul word [ten]
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test dx, dx
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jnz .overflow
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mov dx, ax
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add dx, cx
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jc .overflow
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jmp atoi
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.notdigit:
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mov byte [char_slot], al
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mov si, notdigit_msg
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mov ah, 2
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int 0x21
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int 0x20
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.overflow:
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mov si, overflow_msg
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mov ah, 2
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int 0x21
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int 0x20
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.end:
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std
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mov di, hexstring+3
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xor bh, bh
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mov cx, 4
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itoh:
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mov bl, 0xf
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and bl, dl
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mov al, [hexdigits + bx]
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stosb
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shr dx, 1
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shr dx, 1
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shr dx, 1
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shr dx, 1
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loop itoh
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cld
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mov si, hexstring
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mov ah, 2
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int 0x21
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int 0x20
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notdigit_msg db "Not a digit '"
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char_slot db 0, "'", 0
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overflow_msg db "Value must be in range 0 to 65535", 0
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hexstring db "xxxx", 0
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hexdigits db "0123456789abcdef"
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ten dw 10
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