.TITLE	MRC2.. CHARACTER PROCEDURES IN MACRO
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	.IDENT	/MRC2../
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	.PAGE
	.SBTTL	.		MODIFY  A CHARACTER WITHIN A STRING
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R$MODC::			;REPLACE A CHARACTER IN A STRING
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;			ENTRY CONDITIONS
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;		R0 =  REPLACEMENT CHARACTER
;		R1 -> CHARACTER STRING ADDRESS
;		R2 =  CHARACTER POSITION TO MODIFY
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;			EXIT CONDITIONS
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;		EXITERROR IF INVALID CONDITIONS
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	TST R2			;IS POSITION VALUE VALID
	BLE	10$		;J IF INVALID POS IE <=0
	CMP @R1,R2		;WILL POSITION PASS END OF STRING
	BLT	10$		;J IF END OF STRING
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	SAVE R3			;SAVE REGISTER 3
	MOV R1,R3		;HOLD START ADDRESS OF STRING
	INC R3			;INDEX TO CHARACTER POSITION
	ADD R2,R3		;R3 -> TO ACTUAL CHARACTER ADDRESS
	MOVB R0,@R3		;REPLACE CHARACTER WITH CONTENTS OF R0
	UNSAVE R3		;RESTORE REGISTER 3
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	EXITSUCCESS		;EXIT INDICATING SUCCESS
10$:	EXITERROR		;EXIT INDICATING FAIL
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	.END
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