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    Length: 2560 (0xa00)
    Types: TextFile
    Names: »DELETE.MAC«

└─⟦01b5c9619⟧ Bits:30005906 Microsoft Multiplan v1.05 og HELP
    └─ ⟦this⟧ »DELETE.MAC« 

TextFile

;
;
;	Title		Delete a substring from a string
;	Name:		Delete
;
;
;	Purpose:	Delete a substring from a string given a
;			  starting index and a length
;
;	Entry:		Register pair HL = base address of string
;			Register B = number of bytes to delete
;			Register C = starting index into the string
;				 An index of 1 is the first character
;
;			  A string is maximum  f 255 bytes long plus
;			  a length byte which precedes it.
;
;	Exit:		Substring deleted.
;			if no errors then
;			  CARRY := 0
;			else
;			begin
;			  the following conditions cause an
;			  error with CARRY := 1
;			  if (index = 0) or (index > length(string))
;			    then do not change string
;			  if count is too large then
;			    delete only the characters from
;			    index to end of string
;			end;
;
;	Registers used:	AF,BC,DE,HL
;
;	Time:		Approximately 21 * (lenght(strg)-index-count+1)
;			plus 224 cycles overhead
;
;	Size:		Program 58 bytes
;			Data	 1 byte
;
;
;
DELETE:
	;Initialize error indicator (delerr) to 0
	sub	a
	ld	(delerr),a	;Assume no errors

	;Check if count and index are both non-zero
	or	b		;Test number of bytes to delete
	ret	z		;Return with CARRY = 0 ( noerrors) if
				;  0 bytes to delete
	ld	a,c		;Test starting index
	or	a
	scf			;Carry := 1;
	ret	z		;Error exit (carry := 1) if
				;  starting index = 0

	;Check if starting index within string
	ld	a,(hl)		;Get lenght
	cp	c		;Is index within string ?
	ret	c		;No, take error exit

	;Be shure enough characters are available
	;  if not, delete only to end of string
	;  if index + number of characters - 1 > length(string) then
	;    number of characters := length(string) - index + 1;
	ld	a,c		;Get index
	add	a,b		;Add number of characters to delete
	jr	c,trunc		;Truncate if sum > 255
	ld	e,a		;Save sum as starting index for move
	dec	a
	cp	(hl)		;Compare to lenght
	jr	c,cntok		;Jump if enough characters available
	jr	z,trunc		;Truncate but no errors (exactly enough
				;  characters
	ld	a,0ffh		;Indicate error - not enough characters
	ld	(delerr),a	;  available for deletion

	;Truncate string - no compacting necessary
	;  string lenght = index -1
trunc:
	ld	a,c		;String lenght = index - 1
	dec	a
	ld	(hl),a
	ld	a,(delerr)
	rra			;Carry = 0 if no errors
	ret			;Exit

	;Delete substring by compacting
	;  move all characters above deleted area down
	;New lenght = old lenght - number of bytes to delete
cntok:
	«eof»