67 lines
1.0 KiB
NASM
67 lines
1.0 KiB
NASM
section .bss
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printr:
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.ax: resw 1
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.cx: resw 1
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.dx: resw 1
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.bx: resw 1
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section .text
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; Stack contents
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; ret-addr arg1 arg2 arg3 ...
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printf: mov [printr.ax], ax
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mov [printr.cx], cx
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mov [printr.dx], dx
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mov [printr.bx], bx
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pop bx
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.loop: mov al, [cs:bx]
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inc bx
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cmp al, 0
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je .end
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cmp al, 2
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je .word
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call pputc
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jmp .loop
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.end: push bx
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mov ax, [printr.ax]
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mov cx, [printr.cx]
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mov dx, [printr.dx]
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mov bx, [printr.bx]
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ret
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.word: pop dx
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call pdx
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jmp printf.loop
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pdx: ; this double-call is essentially a 4 times repeating loop
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call .l1
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.l1: call .l2
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.l2: ; set up cl for bit shifts
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mov cl, 4
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; 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 pputc
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; ... add 7 so we continue at 'A'
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add al, 7
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pputc: push bx
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mov ah, 0x0e
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xor bx, bx
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int 0x10
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pop bx
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ret
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