mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-11-23 15:32:08 +00:00
157 lines
4.0 KiB
Plaintext
157 lines
4.0 KiB
Plaintext
*
|
|
*``````````````````````````````*
|
|
* MULT16 :: MULTIPLY WORDS *
|
|
*- -*
|
|
* PERFORM MULTIPLICATION USING *
|
|
* THE SHIFT AND ADD ALGORITHM *
|
|
* *
|
|
* NOTE: WHILE THIS DOES PASS *
|
|
* THE FULL 32BIT PRODUCT BACK *
|
|
* VIA X AND Y, THIS WOULD *
|
|
* RETURN FALSE RESULTS IF ONE *
|
|
* OF THE PARAMETERS HAD BEEN *
|
|
* SIGNED. THUS, USUALLY ONLY *
|
|
* THE LOW WORD IS USED. *
|
|
*- -*
|
|
* CLOBBERS: *
|
|
* *
|
|
* FLAGS: ????---- REG: AXYM *
|
|
*- -*
|
|
* CYCLES: ??? *
|
|
* SIZE: *
|
|
*- -*
|
|
* USAGE: *
|
|
* *
|
|
* LDA #>1000 *
|
|
* PHA *
|
|
* LDA #<1000 ; MCAND *
|
|
* PHA *
|
|
* LDA #>3 *
|
|
* PHA *
|
|
* LDA #<3 ; MLIER *
|
|
* PHA *
|
|
* JSR MUL16 ; = 3000 *
|
|
*- -*
|
|
* ENTRY *
|
|
* *
|
|
* TOP OF STACK *
|
|
* *
|
|
* LOW BYTE OF RETURN ADDRESS *
|
|
* HI BYTE OF RETURN ADDRESS *
|
|
* LOW BYTE OF MULTIPLIER *
|
|
* HIGH BYTE OF MULTIPLIER *
|
|
* LOW BYTE OF MULTIPLICAND *
|
|
* HIGH BYTE OF MULTIPLICAND *
|
|
*- -*
|
|
* EXIT *
|
|
* *
|
|
* TOP OF STACK *
|
|
* *
|
|
* LOW BYTE OF RETURN ADDRESS *
|
|
* HI BYTE OF RETURN ADDRESS *
|
|
* LOW BYTE OF PRODUCT *
|
|
* HIGH BYTE OF PRODUCT (16BIT) *
|
|
* *
|
|
* .Y = LOW BYTE OF HIGH WORD *
|
|
* .X = HIGH BYTE OF HIGH WORD *
|
|
* .A = LOW BYTE OF RET ADDR *
|
|
* *
|
|
* [RETURN] = RESULT (2 BYTES) *
|
|
* [RETLEN] = 2 (RESULT LENGTH) *
|
|
*- -*
|
|
* ADAPTED FROM LEVANTHAL AND *
|
|
* WINTHROP'S /6502 ASSEMBLY *
|
|
* LANGUAGE ROUTINES/. *
|
|
*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
|
|
*
|
|
MULT16
|
|
*
|
|
** GET RETURN ADDRESS
|
|
*
|
|
PLA
|
|
STA RETADR
|
|
PLA
|
|
STA RETADR+1
|
|
*
|
|
** GET PARAMETERS
|
|
*
|
|
PLA
|
|
STA :MLIER
|
|
PLA
|
|
STA :MLIER+1
|
|
PLA
|
|
STA :MCAND
|
|
PLA
|
|
STA :MCAND+1
|
|
*
|
|
** PERFORM MULTIPLICATION USING THE SHIFT
|
|
** AND ADD ALGORITHM, WHICH PRODUCES AN
|
|
** UNSIGNED 32-BIT PRODUCT IN :HIPROD AND
|
|
** :MLIER WITH :HIPROD BEING THE HIGH WORD.
|
|
*
|
|
LDA #0
|
|
STA :HPROD ; ZERO HIGH WORD
|
|
STA :HPROD+1
|
|
LDX #17 ; # OF BITS IN MPLIER
|
|
; PLUS 1. EXTRA LOOP IS
|
|
; TO MOVE LAST CARRY INTO
|
|
; THE PRODUCT.
|
|
CLC ; CLEAR CARRY FOR 1ST TIME
|
|
; THROUGH LOOP.
|
|
:MULLP
|
|
*
|
|
** IF NEXT BIT = 1 THEN
|
|
** HIPROD = HIPROD+MCAND
|
|
*
|
|
ROR :HPROD+1
|
|
ROR :HPROD
|
|
ROR :MLIER+1
|
|
ROR :MLIER
|
|
BCC :DECCNT ; BR IF NEXT BIT OF
|
|
; MULTIPLIER IS 0
|
|
CLC ; NEXT BIT=1 SO ADD MCAND
|
|
; TO PRODUCT
|
|
LDA :MCAND
|
|
ADC :HPROD
|
|
STA :HPROD
|
|
LDA :MCAND+1
|
|
ADC :HPROD+1
|
|
STA :HPROD+1 ; CARRY = OVERFLOW
|
|
; FROM ADD
|
|
:DECCNT
|
|
DEX
|
|
BNE :MULLP ; CONTINUE UNTIL DONE
|
|
|
|
LDY :HPROD ; LOW BYTE OF HIGH WORD
|
|
LDX :HPROD+1 ; HIGH BYTE OF HIGH WORD
|
|
*
|
|
** PUSH LOW WORD OF PRODUCT ONTO THE STACK
|
|
*
|
|
LDA :MLIER+1
|
|
TAX
|
|
STX RETURN+1
|
|
LDA :MLIER
|
|
TAY
|
|
STY RETURN
|
|
LDA :HPROD
|
|
STA RETURN+2
|
|
LDA #2
|
|
STA RETLEN
|
|
*
|
|
** RESTORE RETURN ADDRESS
|
|
*
|
|
LDA RETADR+1
|
|
PHA
|
|
LDA RETADR
|
|
PHA
|
|
*
|
|
LDA :HPROD ;24BIT
|
|
RTS
|
|
*
|
|
** DATA
|
|
*
|
|
:MCAND DS 3
|
|
:MLIER DS 3
|
|
:HPROD DS 2
|
|
*
|