; Return in the EAX register the IP-address (IPv4), obtained from the ASCIIZ
; string starting at an address passed in the RDI register. The string is in
; decimal format with a dot as a delimiter between bytes (e.g.: 192.92.129.2).

option prologue:none, epilogue:none
.code
getipstr proc
_getipstr proc
	MOV	RSI,RDI	; Place the starting address in RSI because of LODSB
	.repeat
		XOR	EAX,EAX	; New current byte - start accumulating from 0
		CDQ
		.repeat
			IMUL	EDX,EDX,10; Shift current byte 1 decimal place
			ADD	DL,AL; Add the new digit to it
			LODSB	; Load the next character assuming it's a digit
			SUB	AL,'0'; Convert from ASCII to BCD
		.until (below?)	; A digit? Continue with the next character
		SHL	ECX,8	; Make room for the current byte
		MOV	CL,DL	; and write it from the right in the IP-address
	.until (AL == -'0')	; If this byte was a null terminator,
	XCHG	EAX,ECX		; return the IP-address in EAX
	RET
_getipstr endp
getipstr endp
end