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47 lines
1.5 KiB
NASM
47 lines
1.5 KiB
NASM
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; receiving the data in 'dx'
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; For the examples we'll assume that we're called with dx=0x1234
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print_hex:
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pusha
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mov cx, 0 ; our index variable
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; Strategy: get the last char of 'dx', then convert to ASCII
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; Numeric ASCII values: '0' (ASCII 0x30) to '9' (0x39), so just add 0x30 to byte N.
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; For alphabetic characters A-F: 'A' (ASCII 0x41) to 'F' (0x46) we'll add 0x40
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; Then, move the ASCII byte to the correct position on the resulting string
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hex_loop:
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cmp cx, 4 ; loop 4 times
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je end
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; 1. convert last char of 'dx' to ascii
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mov ax, dx ; we will use 'ax' as our working register
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and ax, 0x000f ; 0x1234 -> 0x0004 by masking first three to zeros
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add al, 0x30 ; add 0x30 to N to convert it to ASCII "N"
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cmp al, 0x39 ; if > 9, add extra 8 to represent 'A' to 'F'
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jle step2
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add al, 7 ; 'A' is ASCII 65 instead of 58, so 65-58=7
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step2:
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; 2. get the correct position of the string to place our ASCII char
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; bx <- base address + string length - index of char
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mov bx, HEX_OUT + 5 ; base + length
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sub bx, cx ; our index variable
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mov [bx], al ; copy the ASCII char on 'al' to the position pointed by 'bx'
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ror dx, 4 ; 0x1234 -> 0x4123 -> 0x3412 -> 0x2341 -> 0x1234
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; increment index and loop
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add cx, 1
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jmp hex_loop
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end:
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; prepare the parameter and call the function
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; remember that print receives parameters in 'bx'
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mov bx, HEX_OUT
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call print
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popa
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ret
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HEX_OUT:
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db '0x0000',0 ; reserve memory for our new string
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