xlib	rnd

	xref	seed

if QDOS
	include "#fpp_def"
else
	if z88
		include ":*//fpp.def"
	else
		include "#fpp.def"
	endif
endif


; *****************************************************************
;
; Get a random	number [0; 1].	Algorithm	based on ZX SPECTRUM code!
;
; Design & programming by Gunther Strube, Copyright (C) InterLogic 1995
;
; IN:  None.
; OUT: HLhlC =	random number
;
; Registers changed	after return:
;   AF....../IXIY ........ same
;   ..BCDEHL/.... afbcdehl different
;
.rnd				push	af
				ld	bc,0
				ld	de,0
				ld	hl,0
				exx
				ld	hl,(SEED)
				inc	hl							; SEED+1
				ld	de,75
				exx
				fpp(FP_MUL)						; (SEED+1)*75
				ld	b,0
				ld	de,1
				exx
				ld	de,1							; DEdeB =	65537
				exx
				fpp(FP_MOD)						; ((SEED+1)*75) MOD	65537
				exx
				dec	hl
				ld	(SEED),hl						; SEED = (((SEED+1)*75) MOD 65537)-1
				ld	de,0
				exx								; HLhlC =	SEED
				ld	b,0
				ld	de,1							; DEdeB =	65536
				fpp(FP_DIV)
				pop	af							; HLhlC =	SEED/65536
				ret