mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-11-30 15:49:55 +00:00
333 lines
7.4 KiB
Plaintext
333 lines
7.4 KiB
Plaintext
*
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*``````````````````````````````*
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* 16-BIT DIVISION: *
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* *
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* SDIV16, UDIV16, SREM16, AND *
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* UREM16. *
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*- -*
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* SDIV16: DIVIDED 2 SIGNED BIT *
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* WORDS AND RETURN A 16-BIT *
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* SIGNED QUOTIENT. *
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* *
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* UDIV16: DIVIDE 2 UNSIGNED *
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* 16BIT WORDS AND RETURN A *
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* 16BIT UNSIGNED QUOTIENT. *
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* *
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* SREM16: DIVIDE 2 SIGNED *
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* 16BIT WORDS AND RETURN A *
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* 16BIT SIGNED REMAINDER. *
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* *
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* UREM16: DIVIDE 2 UNSIGNED *
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* 16BIT WORKDS AND RETURN A *
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* 16BIT UNSIGNED REMAINDER. *
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*- -*
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* CLOBBERS: *
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* *
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* FLAGS: ????---- REG: AXYM *
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*- -*
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* CYCLES: ??? *
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* SIZE: *
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*- -*
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* USAGE: *
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* *
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** ALL ROUTINES USE THE SAME *
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** FORMAT. *
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* *
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* LDA #>10000 *
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* PHA *
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* LDA #<10000 ; DIVIDEND *
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* PHA *
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* LDA #>1000 ; DIVISOR *
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* PHA *
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* LDA #<1000 *
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* PHA *
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* JSR UDIV16 *
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*- -*
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* ENTRY *
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* *
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* TOP OF STACK *
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* *
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* LOW BYTE OF RETURN ADDRESS *
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* HI BYTE OF RETURN ADDRESS *
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* LOW BYTE OF DIVISOR *
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* HIGH BYTE OF DIVISOR *
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* LOW BYTE OF DIVIDEND *
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* HIGH BYTE OF DIVIDEND *
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*- -*
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* EXIT *
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* *
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* TOP OF STACK *
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* *
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* LOW BYTE OF RETURN ADDRESS *
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* HI BYTE OF RETURN ADDRESS *
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* *
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* IF NO ERRORS, CARRY = 0, *
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* ELSE CARRY=1, QUOTIENT=0, *
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* AND REMAINDER=0 *
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* *
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* .Y = COUNTER; TRASH *
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* .X = COUNTER; TRASH *
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* .A = LOW BYTE OF RET ADDR *
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* *
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* [RETURN] = RESULT (2 BYTES) *
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* [RETLEN] = 2 (RESULT LENGTH) *
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*- -*
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* ADAPTED FROM LEVANTHAL AND *
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* WINTHROP'S /6502 ASSEMBLY *
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* LANGUAGE ROUTINES/. *
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* AS SUCH, IT MAY FALL UNDER A *
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* DIFFERENT LICENSE UNTIL IT *
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* IS RADICALLY REWORKED. *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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UDIVD16
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LDA #0
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BEQ UDIVMD
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UREMD16
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LDA #2
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UDIVMD
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STA _RSLTI
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*
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** GET RETURN ADDRESS
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*
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PLA
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STA RETADR
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PLA
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STA RETADR+1
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*
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** GET PARAMETERS
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*
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PLA
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STA _DVSOR
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PLA
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STA _DVSOR+1
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PLA
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STA _DVEND
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PLA
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STA _DVEND+1
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*
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JSR UDIV
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BCC DIVOK ; BR IF NO ERR
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DIVERR JMP EREXIT
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DIVOK JMP OKEXIT
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*
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** SIGNED DIVISION
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*
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SDIVD16
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LDA #0 ; RESULT IS QUOTIENT
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BEQ SDIVMD ; (INDEX=0)
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*
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** SIGNED REMAINDER
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*
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SREMD16
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LDA #2 ; RES = REMAINDER (I=2)
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BNE SDIVMD
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*
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SDIVMD
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STA _RSLTI ;RESULT INDEX;0=Q,2=R
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*
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** GET RETURN ADDRESS
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*
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PLA
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STA RETADR
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PLA
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STA RETADR+1
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*
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** GET PARAMETERS
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*
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PLA
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STA _DVSOR
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PLA
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STA _DVSOR+1
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PLA
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STA _DVEND
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PLA
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STA _DVEND+1
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*
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*
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** DETERMINE SIGN OF QUOTIENT BY
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** PERFORMING AN EXCLUSIVE OR OF
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** THE HIGH BYTES. IF THE SIGNS
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** ARE THE SAME THEN BIT 7 WILL
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** BE 0 AND THE QUOTIENT IS
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** POSITIVE. IF THE SIGNS ARE
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** DIFFERENT THEN THE QUOTIENT
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** IS NEGATIVE.
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*
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LDA _DVEND+1
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EOR _DVSOR+1
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STA _SQUOT
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*
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** SIGN OF REMAINDER IS THE SIGN
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** OF THE DIVIDEND
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*
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LDA _DVEND+1
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STA _SREMD
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*
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** TAKE THE ABSOLUTE VALUE OF
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** THE DIVISOR
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*
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LDA _DVSOR+1
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BPL CHKDE ; BR IF ALREADY POS
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LDA #0 ; SUB DVSOR FROM ZERO
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SEC
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SBC _DVSOR
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STA _DVSOR
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LDA #0
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SBC _DVSOR+1
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STA _DVSOR+1
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*
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** TAKE ABS VALUE OF THE DIVIDEND
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*
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CHKDE
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LDA _DVEND+1
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BPL DODIV ; BR IF DVEND IS POS
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LDA #0 ; SUB DVEND FROM ZERO
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SEC
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SBC _DVEND
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STA _DVEND
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LDA #0
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SBC _DVEND+1
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STA _DVEND+1
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*
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** DIVIDE ABS VALUES
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*
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DODIV
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JSR UDIV
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BCS EREXIT ; EXIT IF DIV BY 0
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*
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** NEGATE QUOTIENT IF IT IS NEGATIVE
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*
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LDA _SQUOT
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BPL DOREM ; BR IF Q IS POS
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LDA #0
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SEC
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SBC _DVEND
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STA _DVEND
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LDA #0
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SBC _DVEND+1
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STA _DVEND+1
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*
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DOREM
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*
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** NEGATE REMAINDER IF IT IS NEG
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*
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LDA _SREMD
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BPL OKEXIT ; BR IF REM IS POS
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LDA #0
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SEC
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SBC _DVEND+2
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STA _DVEND+2
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LDA #0
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SBC _DVEND+3
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STA _DVEND+3
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JMP OKEXIT
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*
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** ERROR EXIT (CARRY=1, RSLTS ARE 0)
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*
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EREXIT
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LDA #0
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STA _DVEND
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STA _DVEND+1 ;QUOTIENT = 0
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STA _DVEND+2
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STA _DVEND+3 ; REMAINDER=0
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STA RETURN
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STA RETURN+1
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LDA #2
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STA RETLEN
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SEC ; CARRY=1 IF ERROR
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BCS DVEXIT
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*
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** GOOD EXIT (CARRY = 0)
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*
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OKEXIT
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CLC ; CARRY = 0, NO ERRORS
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*
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DVEXIT
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*
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** STORE RESULT
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*
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LDX _RSLTI ;GET INDEX TO RESULT
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; 0=QUOTIENT, 2=REMAINDER
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*
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** STORE RESULT
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*
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LDA _DVEND,X
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TAY
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LDA _DVEND+1,X
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TAX
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STY RETURN
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STX RETURN+1
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LDA #2
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STA RETLEN
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*
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** RESTORE RETURN ADDRESS
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*
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LDA RETADR+1
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PHA
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LDA RETADR
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PHA
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*
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RTS
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*
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********************************
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* UDIV ROUTINE
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********************************
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UDIV
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*
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** ZERO UPPER WORD DIVIDEND
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** THIS WILL BE CALLED
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** DIVIDEND(1) BELOW
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*
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LDA #0
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STA _DVEND+2
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STA _DVEND+3
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*
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** FIRST CHECK FOR DIV BY 0
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*
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LDA _DVSOR
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ORA _DVSOR+1
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BNE OKUDIV ; BR IF DVSOR NOT 0
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SEC
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RTS
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*
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** PERFORM THE DIVISION BY
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** TRIAL SUBTRACTIONS
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*
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OKUDIV
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LDX #16 ; LOOP THROUGH 16 BITS
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DIVLP
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ROL _DVEND ;SHFT CARRY INTO BIT 0 OF DVEND
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ROL _DVEND+1 ;WHICH WILL BE THE QUOTIENT AND
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ROL _DVEND+2 ;SHFT DVEND AT THE SAME TIME
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ROL _DVEND+3
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CHKLT
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SEC
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LDA _DVEND+2
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SBC _DVSOR
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TAY ; SAVE LOW BYTE IN Y
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LDA _DVEND+3
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SBC _DVSOR+1 ;SUB HIGHBYTES W RES IN A
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BCC DECCNT ; BR IF DVEND < DVSOR AND CARRY
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STY _DVEND+2 ; ELSE
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STA _DVEND+3 ;VEN(1)=DVEND(1)-DVSOR
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*
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DECCNT
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DEX
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BNE DIVLP
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*
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ROL _DVEND ;SHFT IN LAST CAR FOR QUOT
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ROL _DVEND+1
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CLC ; NO ERRORS, CLEAR CARRY
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RTS
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*
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** DATA
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*
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_DVSOR DS 2 ; DIVISOR
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_DVEND DS 4 ; DIVIDEND[0] AND QUOTIENT
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; DIVIDEND[1] AND REMAINDER
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_SQUOT DS 1 ; SIGN OF QUOTIENT
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_SREMD DS 1 ; SIGN OF REMAINDER
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_RSLTI DS 1 ; RESULT INDEX
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*
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