xorshi.mid

.BEGIN XORSHIFT
SUBTTL XORSHIFT

;;; Xorshift implementation with 36-bit output and 2^72-1 period.
;;; Parameters provided by Sebastiano Vigna.  This is an .INSRT file
;;; for MIDAS programs.  It expects A, T and P to be suitably defined
;;; accumulators.  The result is returned in A.

STATE:	-1,, ? 1

;Algorithm parameters.
PARM.A==7
PARM.B==8
PARM.C==3

XORSHIFT:
	PUSH P,T		;Save T.
	MOVE T,STATE
	EXCH T,STATE+1
	EXCH T,STATE
	LSH T,PARM.A		;Do the xorshift linear transformation.
	XOR T,STATE+1
	XOR T,STATE
	MOVEM T,STATE+1
	LSH T,-PARM.B
	XORM T,STATE+1
	MOVE T,STATE
	LSH T,-PARM.C
	XORM T,STATE+1
	POP P,T			;Restore T.
	MOVE A,STATE		;Compute xorshift+ scrambled result.
	ADD A,STATE+1
	POPJ P,

.END XORSHIFT