Difference between revisions of "Programming:Fast Square Root"

Revision as of 18:34, 4 August 2006

Input: A = The number you want to find the square root of

Output: A = Square root of the number supplied in A

Destroys: A,B,DE

Call: CALL SqrtA

;this routine written 10 - 28 - 2003
;ported from the 68k version (by Frank Yaul) by konrad meyer
;this routine is not as memory efficient as it could be; this is
;done to save cycles

;note: this routine is using the fastest available method
;and will come within 1 below the #
;note: this routine is inaccurate in #s below 4

SqrtA:
	LD	(Asqr),A
	SRL	A
	JR	DataOver
Asqr:
	.DB	0
Bsqr:
	.DB	0
Csqr:
	.DB	0
DataOver:
	LD	(Bsqr),A
	LD	B,A
	LD	(Csqr),A
iterate:
	LD	A,(Asqr)
	LD	B,(Bsqr)
	LD	D,A
	LD	E,B
divideDbyEreturnA:
	RL	D
	RLA
	SUB	E
	JR	nc,$+3
	ADD	A,E
	LD	E,A
	LD	A,D
	CPL
	LD	B,(Bsqr)
	ADD	A,B
	SRL	A
	LD	(Bsqr),A
	LD	A,(Csqr)
	DEC	A
	LD	B,(Bsqr)
	CP	B
	JR	z,done
	LD	(Csqr),B
	JR	iterate
done:
	LD	A,(Bsqr)
	RET