;==============================================================================
;                                 randy2.asm
;                          Random Number Generator
;GENERATES PSEUDO-RANDOM INTERGERS IN THE RANGE LOWER TO UPPER
;INPUT: TWO STACK PARAMETERS - LOWER AND UPPER ENDS OF RANGE
;OUTPUT: AX-REGISTER CONTAINS RANDOM INTERGERS
;CALLING SEQUENCE: PUSH    <LOWER END OF RANGE>
;                  PUSH    <UPPER END OF RANGE>
;                  CALL    RANDY
;==============================================================================
				.MODEL   SMALL,   BASIC
;==============================================================================
;            D A T A   S E G M E N T    D E F I N I T I O N
			.DATA	
			 EXTRN		SEED:WORD
			 EXTRN		randomNumber:WORD	

MULTIPLIER		DW		25173			;MULTIPLIER AND
ADDEND			DW		13849			;ADDEND FOR MIXED
										;LINEAR CONGRUENTIAL METHOD
lower			DW		0
upper			DW		9999
range			DW		?
;==============================================================================
;           C O D E     S E G M E N T    D E F I N I T I O N
			.CODE	
			;ASSUME	DS:randy_data
			
reseed		proc	
					
			push	ax
			push	bx
			push	cx
			push	dx
			cmp		bl,	1
			jae		given
			jmp		clock
			
given:		mov		seed,	ax				;subprocedure use the supplied
			jmp		exit
			
clock:		mov		ah,	0					;else use clock for seed value
			int		1ah
			mov		seed,	dx
			
exit:		pop		dx
			pop		cx
			pop		bx
			pop		ax
			ret	
						
reseed		endp						
			
			
random 		proc
			push	ax					
			push	bx					
			push	cx
			push	dx
			PUSHF						;SAVE FLAGS	
			;MOV		AX,	SEG	randy_data	;SET DS-REGISTER TO POINT
			;MOV		DS,	AX				;TO LOCAL DATA SEGMENT
			mov		ax,	seed
			mul		MULTIPLIER	
			add		ax,		ADDEND		;calculate seed value
			mov		seed,	ax
			
			mov		ax,	upper
			sub		ax,	lower
			add		ax,	1
			mov		range,	ax			;range=upper-lower+1
			
			mov		ax,	seed			
			mul		range
			add		dx,	lower
			mov		randomNumber,	dx  ;randomNumber=(seed*range)mod(65536)+lower
			POPF						;RESTORE FLAGS
			pop		dx
			pop		cx
			pop		bx
			pop		ax
										;RESTORE REGISTERS (ASSEMBLER
										;  GENERATES INSTRUCTIONS TO
										;  RESTORE REGISTERS - USES
			ret							;RETURN (randy2)
random 		endp						;END random
			end