;TIMEDIF.A v1.00
; ESKAY 02-12-85
;
	MODULE	"TIMEDIF"
;
; Purpose:
; Evaluate two ASCII character strings in HH:MM:SS format and
; return their difference.
;
; Entry point:	TIMDIF
; Externals:	STTIME
;		ENTIME
;		ELAPTM
;
; Input parameters:
; STTIME holds a time string of HH:MM:SS format. STTIME must point
; to the tens hours digit. The time string must be in 24 hour format.
; The time stored there should be the beginning time of an event.
;
; ENTIME holds a string with the same format. The time stored there
; should be the end of an event.
;
; On return, ELAPTM will be filled with the elapsed time in
; hours and minutes and the accumulator will be cleared with the
; ZERO flag SET. If either entry parameter contained an illegal
; quantity, the CARRY flag will be SET and ELAPTM will be undefined.
; NOTE: TIMDIF will not place delimiters into ELAPTM!
;
; Only the first 8 characters of the strings are processed and checked
; for proper range. Be sure to zero the seconds field if not needed!
;
; NOTE:
; If ENTIME is smaller than STTIME, then 24 hours are added to ENTIME.
;
; This routine is intended for application where the event time will
; never be greater than 23:59:59 (RCPM and BBS use mainly).
;
	LOC	Code#
;
; Entry point. All registers meet their doom...
;
TIMDIF::
	MOV	BX,&STTIME#	;POINT TO START TIME
	CALL	CHFORM		;CHECK PROPER FORMAT
	JNC	__X		;RETURN IF ERROR
	RET
;
__X:	MOV	BX,&ENTIME#	;POINT TO END TIME
	CALL	CHFORM		;CHECK THAT TOO
	JNC	__Y
	RET
;
; The stage is set - let's get down to business...
;
__Y:	MOV	BX,&STTIME#+6	;POINT TO SECONDS START
	CALL	GETBIN		;GET BINARY
	MOV	DH,AL		;SAVE IT
	MOV	BX,&ENTIME#+6	;SECONDS END
	CALL	GETBIN		;GET BINARY
	MOV	DL,=0		;RESET OUR PRIVATE BORROW FLAG
	SUB	AL,DH		;SUBTRACT
	JC	__Z		;SKIP IF NO BORROW
	JMP	SKBS
;
__Z:	DEC	DL		;SET OUR BORROW FLAG
	ADD	AL,=60		;MAKE MOD 60
SKBS:	MOV	BX,&ELAPTM#+7	;STORE AS RESULT
	CALL	STORA
;
; Do the same stuff for minutes
;
	MOV	BX,&STTIME#+3	;MINUTES START
	CALL	GETBIN		;GET BINARY
	MOV	DH,AL		;SAVE BINARY
	MOV	BX,&ENTIME#+3	;MINUTES END
	CALL	GETBIN		;GET BINARY
	INC	DL		;IF NOT BORROW...
	JZ	__X			;THEN SKIP...
	JMP	SKBM1
;
__X:	INC	DH		;...ELSE ADD BORROWED VALUE
SKBM1:	MOV	DL,=0		;MAKE SURE BORROW FLAG RESET
	SUB	AL,DH		;SUBTRACT
	JC	__X		;SKIP IF NO BORROW
	JMP	SKBM2
;
__X:	DEC	DL		;SET BORROW
	ADD	AL,=60		;MAKE MOD 60
SKBM2:	MOV	BX,&ELAPTM#+4	;STORE ELAPSED MINUTES
	CALL	STORA
;
; Finally, here go the hours.
;
	MOV	BX,&STTIME#	;HOURS START
	CALL	GETBIN		;GET 'EM
	MOV	DH,AL		;SAVE START HOURS
	MOV	BX,&ENTIME#	;HOURS END
	CALL	GETBIN		;GET BINARY
	INC	DL		;IF NOT BORROW...
	JZ	__X			;...THEN SKIP...
	JMP	SKBH1
;
__X:	INC	DH		;...ELSE ADD BORROWED HOUR
SKBH1:	SUB	AL,DH		;SUBTRACT
	JC	__X		;JUMP IF NO BORROW
	JMP	SKBH2
;
__X:	ADD	AL,=24		;ELSE ADD 24 HOURS
SKBH2:	MOV	BX,&ELAPTM#+1	;SAVE AS HOURS
	CALL	STORA
	XOR	AL,AL		;MAKE SURE ERROR IS RESET
	RET			;END OF EXECUTION, BACK TO CALLER.
;
; Get the ASCII value at HL as a binary into A
;
GETBIN:	MOV	AL,[BX]		;GET TENS
	AND	AL,=0X0F	;STRIP ASCII OFFSET
	MOV	CH,AL		;SAVE TENS
	XOR	AL,AL		;SET ACCUMULATOR
	MOV	CL,=10		;SET UP CHEAP MULTIPLIER
MUL:	ADD	AL,CL
	DEC	CH
	JZ	__X
	JMP	MUL
;
__X:	MOV	CH,AL		;SAVE TENS
	INC	BX		;POINT TO UNITS
	MOV	AL,[BX]		;GET UNITS
	AND	AL,=0X0F		;SAME TREATMENT
	ADD	AL,CH		;ADD THE TENS
	RET
;
; Check format of HH:MM:SS string. Checks all digits for presence
; and validity.
;
CHFORM:	MOV	AL,[BX]		;GET 10S H
	CMP	AL,='0'
	JNC	__X
	RET
;
__X:	CMP	AL,='3'
	CMC	
	JNC	__Y
	RET
;
__Y:	INC	BX
	MOV	AL,[BX]		;GET 1S H
	CALL	CK10		;CHECK DECIMAL
	JNC	__Z
	RET
;
__Z:	INC	BX		;GET COLON
	MOV	AL,[BX]
	CMP	AL,=':'
	STC	
	JZ	__A
	RET
;
__A:	INC	BX		;POINT TO 10S M
	MOV	AL,[BX]
	CALL	CK6		;CHECK HEX
	JNC	__B
	RET
;
__B:	INC	BX
	MOV	AL,[BX]		;1S M
	CALL	CK10
	JNC	__C
	RET
;
__C:	INC	BX
	MOV	AL,[BX]		;GET DELIMITER
	CMP	AL,=':'
	STC	
	JZ	__D
	RET
;
__D:	INC	BX
	MOV	AL,[BX]		;GET 10S S
	CALL	CK6
	JNC	__E
	RET
;
__E:	INC	BX
	MOV	AL,[BX]
CK10:	CMP	AL,='0'
	JNC	__X
	RET
;
__X:	CMP	AL,='9'+1
	CMC	
	RET
;
CK6:	CMP	AL,='0'
	JNC	__X
	RET
;
__X:	CMP	AL,='7'
	CMC	
	RET
;
; Store accumulator as ASCII digits at HL and HL+1
;
STORA:	MOV	CH,=-1
TLP:	INC	CH
	SUB	AL,=10		;SUBTRACT 10
	JC	__X		;UNTIL BORROW
	JMP	TLP
;
__X:	ADD	AL,=10		;MAKE MOD 10
	OR	AL,='0'		;MAKE ASCII
	MOV	[BX],AL
	DEC	BX
	MOV	AL,='0'
	ADD	AL,CH
	MOV	[BX],AL
	RET
;
	END

.