.MCALL	.MODULE
.MODULE RAN,VERSION=01,COMMENT=<RANDOM NUMBER FUNCTION>,LIB=YES,IDENT=NO

; Copyright (c) 1998 by Mentec, Inc., Nashua, NH.
; All rights reserved
;
; This software is furnished under a license for use only on a
; single computer system and  may  be  copied  only  with  the
; inclusion of the above copyright notice.  This software,  or
; any other copies thereof, may not be provided  or  otherwise
; made available to any other person except for  use  on  such
; system and to one who agrees to these license  terms.  Title
; to  and  ownership of the software shall at all times remain
; in Mentec, Inc.
;
; The information in this document is subject to change without
; notice and should not be construed as a commitment by Digital
; Equipment Corporation, or Mentec, Inc.
;
; Digital and Mentec  assume  no  responsibility for the use or
; reliability of its software on equipment which is not supplied
; by Digital  or Mentec,  and listed  in the  Software  Product
; Description.
;
; AUTHOR:
;   R. SCHAEFER	24-OCT-78
;	DEVELOPED FROM THE VAX-RTL VERSION DUE TO:
;	P.F. CONKLIN, T.HASTINGS, D. MACLAREN
;
;+
; FUNCTION:
;	RANDOM NUMBER GENERATOR
; CALLING SEQUENCE:
;	RAN(I1,I2)
;   OR
;	RAN(J)
;   WHERE
;	I1,I2 ARE INTEGER*2 VALUES FOR THE GENERATOR BASE
;	J IS AN INTEGER*4 VALUE FOR THE GENERATOR BASE
;
;	RETURNS A PSEUDO-RANDOM NUMBER IN THE RANGE [0.0,1.0)
;
; ALGORITHM:
;	THIS IS A GENERAL RANDOM NUMBER GENERATOR.  IT IS
;	OF THE MULTIPLICATIVE CONGRUENTIAL TYPE, AND HENCE
;	IS FAST, ALTHOUGH PRONE TO CERTAIN CLASSES OF
;	NON-RANDOM SEQUENCES.  THIS NON-RANDOM BEHAVIOR
;	TYPICALLY ARISES WHEN CONSIDERING TRIPLES OF NUMBERS
;	GENERATED BY THIS METHOD.
;
;	FOR MORE INFORMATION, CONSULT:
;	RANDOM NUMBER GENERATION (PP. 1192-1197)
;	BY G. MARSAGLIA IN
;	ENCYCLOPEDIA OF COMPUTER SCIENCE
;	EDITED BY ANTHONY RALSTON
;	PETROCELLI (NEW YORK 1976)
;
;-

;;;	ERRDEF

;;;	OTS$I

	.PSECT	SYS$I,I		;RH001

	.GLOBL	$SYSLB		; Include system library work area.
	.GLOBL	RAN$
RAN::
	MOV	(R5)+,R0	;GET ARG COUNT
	DECB	R0		;ONE I*4 ARG?
	BNE	10$		;TRY FOR 2 ARGS
	MOV	(R5),R0		;GET ARG ADDRESS
	CALLR	RAN$		;AND COMPUTE THE RANDOM NUMBER

10$:	DECB	R0		;2 I*2 ARGS?
	BNE	20$		;ERROR IF NOT 2
	CMP	(R5)+,(R5)+	;POINT PAST BOTH ARGS
	MOV	@-(R5),-(SP)	;PUSH HIGH ORDER SEED
	MOV	@-(R5),-(SP)	;PUSH LOW ORDER SEED
	MOV	SP,R0		;MAKE PTR TO THE I*4 VALUE
	CALL	RAN$		;COMPUTE THE FUNCTION
	MOV	(SP)+,@(R5)+	;RESTORE THE LOW ORDER NEW SEED
	MOV	(SP)+,@(R5)+	;RESTORE THE HIGH ORDER NEW SEED
20$:	RETURN

	.END