; Return in register RAX the integer part of the square root of the number
; in registers RSI:RDI, which integer part is equal to the number of the
; consecutive odd numbers that can be subtracted from that number.

option prologue:none, epilogue:none
.code
sqrt128	proc
_sqrt128 proc
	MOV	RAX,-1	; Initialise the 65-bit subtrahend with -1
	MOV	RDX,RAX	; in RDX:RAX
	.repeat
		ADD	RAX,2	; Get the next odd number
		ADC	RDX,0
		SUB	RDI,RAX	; Subtract the low words
		SBB	RSI,RDX	; Subtract the high words
	.until (carry?)	; No carry yet? Continue the loop!
	SHRD	RAX,RDX,1;Divide the subtrahend to 2
	RET		; RAX = the number of the subtracted odd numbers
_sqrt128 endp
sqrt128	endp
end