; Draws a circle using the Pythagorean theorem (summing squares to determine
; distance from origin and thus colouring in a pixel white or black depending on
; whether or not it's in the circle). This is a good example of the value of
; HashLife; only 32 multiplications actually have to be done, even though in
; theory it should be 2048 (two coordinates per pixel).

start:	ld 31,x1     ; x coord.
	ld 1,x5      ; Constant.
	ld 32,x7     ; Constant.
	ld 1024,x9   ; Constant (32 squared, used as the threshold).
forx:	ld 0,x2      ; y coord.
	xor x0,x0,x3 ; Accumulator for column.
	ld 1,x4      ; Bitmask.
fory:	mul x1,x1,x8
	mul x2,x2,xE
	add x8,xE,x8 ; x8 := sum of squares of x and y.
	add x2,x5,x2
	sub x8,x9,x0
	;sub x1,x2,x0
	jf blk
	or x4,x3,x3
blk:	add x4,x4,x4 ; <<= 1
	jnf fory
	; Column done; now draw it and move on.
	out x3,!0xe
	out x1,!0xe
	sub x1,x5,x1
	jf forx
	hlt