AppleIIAsm-Collection/disks/disk1__stdio_common/T.COMMON.MEMFILL

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*``````````````````````````````*
* MEMFILL :: FILL MEMORY LOC *
*- -*
* FILLS A BLOCK OF MEMORY WITH *
* THE SPECIFIED VALUE; USED *
* OFTEN TO CLEAR LARGE BLOCKS. *
*- -*
* CLOBBERS: *
* *
* FLAGS: ????---- REG: AXYM *
*- -*
* CYCLES: ??? *
* SIZE: *
*- -*
* USAGE: *
* *
* LDA #>$6A00 *
* PHA *
* LDA #<$6A00 *
* PHA *
* LDA #>1024 *
* PHA *
* LDA #<1024 *
* PHA *
* LDA #0 *
* PHA *
* JSR MEMFILL *
*- -*
* ENTRY *
* *
* TOP OF STACK *
* *
* LOW BYTE OF RETURN ADDRESS *
* HI BYTE OF RETURN ADDRESS *
* FILL VALUE FOR MEMORY *
* ARRAY SIZE *
* LOW BYTE OF STARTING POINT *
* HIGH BYTE OF STARTING POINT *
*- -*
* EXIT *
* *
* TOP OF STACK *
* *
* LOW BYTE OF RETURN ADDRESS *
* HI BYTE OF RETURN ADDRESS *
* *
* Y = COUNTER; TRASH *
* X = COUNTER; TRASH *
* A = LOW BYTE OF RET ADDR *
*- -*
* ADAPTED FROM LEVANTHAL AND *
* WINTHROP'S /6502 ASSEMBLY *
* LANGUAGE ROUTINES/. *
* AS SUCH, THIS MAY NOT FALL *
* UNDER THE APACHE 2.0 LICENSE *
* AGREEMENT, SINCE THE BOOK *
* WAS WRITTEN BEFORE THE *
* LICENSE! *
* *
* THAT SAID, LEVENTHAL WROTE *
* THAT THE PURPOSE OF THE BOOK *
* WAS TO COPY THE SOURCE CODE, *
* AS REINVENTING THE WHEEL IS *
* TEDIOUS, AND HE PLACED NO *
* RESTRICTIONS ON ITS USE. *
*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
*
MEMFILL
*
** SAVE RETURN ADDRESS
*
PLA
STA :RETADR
PLA
STA :RETADR+1
*
** GET PARAMETERS
*
PLA
STA :VALUE
PLA
STA :ARYSZ
PLA
STA :ARYSZ+1
PLA
STA ADDR1 ; ZERO PAGE POINTER
PLA ; DEFINED IN
STA ADDR1+1 ; DECS
*
** FILL WHOLE PAGES FIRST
*
LDA :VALUE ; GET VAL FOR FILL
LDX :ARYSZ+1 ; X=# OF PAGES TO DO
BEQ :PARTPG ; BRANCH IF HIGHBYTE OF SZ = 0
LDY #0
:FULLPG
STA (ADDR1),Y
INY ; INC TO NEXT BYTE
BNE :FULLPG ; BRANCH IF NOT DONE W/ PAGE
INC ADDR1+1 ; ADVANCE TO NEXT PAGE
DEX
BNE :FULLPG ; BRANCH IF NOT DONE W/ PAGES
*
** DO THE REMAINING PARTIAL PAGE
** REGISTER A STILL CONTAINS VALUE
*
:PARTPG
LDX :ARYSZ ;GET # OF BYTES IN FINAL PAGE
BEQ :EXIT ; BRANCH IF LOW BYTE = 0
LDY #0
:PARTLP
STA (ADDR1),Y ; STORE VAL
INY ; INCREMENT INDEX
DEX ; DECREMENT COUNTER
BNE :PARTLP ; BRANCH IF NOT DONE
:EXIT
*
** RESTORE RETURN ADDRESS
*
LDA :RETADR+1
PHA
LDA :RETADR
PHA
RTS
*
** DATA
*
:VALUE DS 1 ; FILL VALUE
:ARYSZ DS 2 ; ARRAY SIZE
:RETADR DS 2