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COMMENT % SIMULA specification;
OPTIONS(/E:QUICK,nextrandom);
INTEGER PROCEDURE nextrandom(nstep,u); INTEGER nstep,u;
COMMENT Returns the NSTEP:th value from the random stream,
starting with U.
;
!    BEGIN   INTEGER an,acc;
!	! an saves actual product;
!	! acc saves a^(2^i) for i = 0,1,2...Log2[nstep]+1;
!	! nstep = sum(2^i) for certain i's;
!	a:=5^15;
!	b:=2^35;
!	an:= 1;!    acc:= a;
!	nstep:= Mod(nstep,b//4);	!Take Mod(cycle length = 2^33);
!	WHILE nstep NE 0 DO
!	BEGIN
!	    IF Mod(nstep,2) = 1 THEN an:= Mod(an*acc,b);
!	    acc:= Mod(acc*acc,b);
!	    nstep:= nstep//2;		!Shift to next bit;
!	END loop;
!	nextrandom:= Mod(an*u,b);
!    END of nextrandom;

!%;! MACRO-10 code !%;!

	TITLE	nextrandom
	ENTRY	nextrandom
	SUBTTL	SIMULA utility, Lars Enderin Mar 1976

;!*** Copyright 1976 by the Swedish Defence Research Institute. ***
;!*** Copying is allowed.					***


	sall
	search	simmac,simmcr,simrpa
	macinit

	;! Local definitions ;!

	nstep==XWAC1
	u==XWAC2
	an==XWAC3
	acc==X0

	a==1
	REPEAT ^d15,<a==a*5>

nextrandom:
	PROC
	EXCH	XWAC1,(XTAC)
	EXCH	XWAC2,1(XTAC)
	SAVE	<XWAC3,XWAC4>
	LI	an,1
	L	acc,[a]
	TLZ	nstep,700k	;! Zero 3 bits starting at bit 0
	WHILE	;! nstep > 0
		JUMPE	nstep,FALSE
	DO
		IF	;! Last bit = 1
			TRNN	nstep,1
			GOTO	FALSE
		THEN
			MUL	an,acc
			L	an,an+1
			TLZ	an,400k
		FI
		MUL	acc,acc
		L	acc,acc+1
		TLZ	acc,400k
		ASH	nstep,-1
	OD
	L	u
	SKIPGE
	ADD	[377777777777]
	TRO	1
	MUL	an
	TLZ	X1,400k
	ST	X1,XWAC1
	RESTORE
	EXCH	XWAC2,1(XTAC)
	EXCH	XWAC1,(XTAC)
	POPJ	XPDP,
	EPROC
	LIT
	END;