.TITLE	MG13.. STRING PROCEDURES IN MACRO
	.IDENT	/MG13../
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	.SBTTL	INDICATE PARITY STATE OF REGISTER R0
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R$PARITY::			;PROCEDURE TO INDICATE PARITY STATE
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;		ENTRY CONDITIONS
;		R0 -> CHARACTER TO ANALYSISE
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;		EXIT CONDITIONS
;		STATUS = SUCCESS IF PARITY IS EVEN
;		STATUS = ERROR   IF PARITY IS ODD
;		-8(SP) =  ONES COUNT OF INPUT VALUE
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	SAVE R0,R1		;PROTECT REGISTERS R0 AND R1
	MOV #16.,R1		;COUNT OF NUMBER OF POSIBLE BITS IN R0
	CLR -(SP)		;SHIFT POINTER TO GIVE WORK REGISTER
10$:	BIT #1,R0		;IS BOTTOM BIT SET ?????
	BEQ	20$		;J IF BOTTOM BIT CLEAR
	INC @SP			;BUMP UP NUMBER OF ONES
20$:	ASR R0			;SHIFT ALL BITS IN R0 ONE PLACE RIGHT (DOWN)
	SOB R1,10$		;LOOP 16 TIMES HENCE CHECKING ALL BITS
	TST (SP)+		;FUDGE WORK SPACE POINTER
	SETSUCCESS		;ASSUME THAT NUMBER OF ONES IS EVEN
	BIT #1,-2(SP)		;FIND OUT IF ABOVE IS TRUE
	BEQ	30$		;J IF EVEN NUMBER OF BITS
	SETERROR		;INDICATE ODD PARITY
30$:	UNSAVE R0,R1		;RESTORE USED REGISTERS
	RETURN			;PARITY PROCESS COMPLETE GO HOME
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	.END
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