mirror of
https://github.com/rigreco/UniDisk.git
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163 lines
6.2 KiB
NASM
163 lines
6.2 KiB
NASM
* @com.wudsn.ide.asm.hardware=APPLE2
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***********************
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* *
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* APPLE-II FLOATING *
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* POINT ROUTINES *
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* *
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* COPYRIGHT 1977 BY *
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* APPLE COMPUTER INC. *
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* *
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* ALL RIGHTS RESERVED *
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* *
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* S. WOZNIAK *
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* *
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***********************
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* TITLE "FLOATING POINT ROUTINES for //c memory"
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*
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SIGN EQU $EB ; $F3
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** FP2 4 Bytes **
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X2 EQU $EC ; $F4
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M2 EQU $ED ; $F5 - $7
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** FP1 4 Bytes + E extension **
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X1 EQU $FA ; $F8
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M1 EQU $FB ; $F9 - $FB
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E EQU $FE ; $FC
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OVLOC EQU $3F5
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ORG $8000
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ADD CLC ;CLEAR CARRY
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LDX #$2 ;INDEX FOR 3-BYTE ADD.
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ADD1 LDA M1,X
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ADC M2,X ;ADD A BYTE OF MANT2 TO MANT1
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STA M1,X
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DEX ;INDEX TO NEXT MORE SIGNIF. BYTE.
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BPL ADD1 ;LOOP UNTIL DONE.
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RTS ;RETURN
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MD1 ASL SIGN ;CLEAR LSB OF SIGN.
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JSR ABSWAP ;ABS VAL OF M1, THEN SWAP WITH M2
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ABSWAP BIT M1 ;MANT1 NEGATIVE?
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BPL ABSWAP1 ;NO, SWAP WITH MANT2 AND RETURN.
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JSR FCOMPL ;YES, COMPLEMENT IT.
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INC SIGN ;INCR SIGN, COMPLEMENTING LSB.
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ABSWAP1 SEC ;SET CARRY FOR RETURN TO MUL/DIV.
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SWAP LDX #$4 ;INDEX FOR 4 BYTE SWAP.
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SWAP1 STY E-1,X
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LDA X1-1,X ;SWAP A BYTE OF EXP/MANT1 WITH
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LDY X2-1,X ;EXP/MANT2 AND LEAVE A COPY OF
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STY X1-1,X ;MANT1 IN E (3 BYTES). E+3 USED
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STA X2-1,X
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DEX ;ADVANCE INDEX TO NEXT BYTE
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BNE SWAP1 ;LOOP UNTIL DONE.
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RTS ;RETURN
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FLOAT LDA #$8E ;INIT EXP1 TO 14, <--------------- int to fp
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STA X1 ;THEN NORMALIZE TO FLOAT.
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NORM1 LDA M1 ;HIGH-ORDER MANT1 BYTE.
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CMP #$C0 ;UPPER TWO BITS UNEQUAL?
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BMI RTS1 ;YES, RETURN WITH MANT1 NORMALIZED
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DEC X1 ;DECREMENT EXP1.
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ASL M1+2
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ROL M1+1 ;SHIFT MANT1 (3 BYTES) LEFT.
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ROL M1
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NORM LDA X1 ;EXP1 ZERO?
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BNE NORM1 ;NO, CONTINUE NORMALIZING.
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RTS1 RTS ;RETURN.
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FSUB JSR FCOMPL ;CMPL MANT1,CLEARS CARRY UNLESS 0 <---- sub
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SWPALGN JSR ALGNSWP ;RIGHT SHIFT MANT1 OR SWAP WITH
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FADD LDA X2 ;<------------------------------------- add
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CMP X1 ;COMPARE EXP1 WITH EXP2.
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BNE SWPALGN ;IF #,SWAP ADDENDS OR ALIGN MANTS.
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JSR ADD ;ADD ALIGNED MANTISSAS.
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ADDEND BVC NORM ;NO OVERFLOW, NORMALIZE RESULT.
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BVS RTLOG ;OV: SHIFT M1 RIGHT, CARRY INTO SIGN
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ALGNSWP BCC SWAP ;SWAP IF CARRY CLEAR,
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* ELSE SHIFT RIGHT ARITH.
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RTAR LDA M1 ;SIGN OF MANT1 INTO CARRY FOR
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ASL ;RIGHT ARITH SHIFT.
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RTLOG INC X1 ;INCR X1 TO ADJUST FOR RIGHT SHIFT
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BEQ OVFL ;EXP1 OUT OF RANGE.
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RTLOG1 LDX #$FA ;INDEX FOR 6:BYTE RIGHT SHIFT.
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ROR1 ROR E+3,X
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INX ;NEXT BYTE OF SHIFT.
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BNE ROR1 ;LOOP UNTIL DONE.
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RTS ;RETURN.
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FMUL JSR MD1 ;ABS VAL OF MANT1, MANT2 <-------------- mul
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ADC X1 ;ADD EXP1 TO EXP2 FOR PRODUCT EXP
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JSR MD2 ;CHECK PROD. EXP AND PREP. FOR MUL
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CLC ;CLEAR CARRY FOR FIRST BIT.
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MUL1 JSR RTLOG1 ;M1 AND E RIGHT (PROD AND MPLIER)
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BCC MUL2 ;IF CARRY CLEAR, SKIP PARTIAL PROD
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JSR ADD ;ADD MULTIPLICAND TO PRODUCT.
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MUL2 DEY ;NEXT MUL ITERATION.
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BPL MUL1 ;LOOP UNTIL DONE.
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MDEND LSR SIGN ;TEST SIGN LSB.
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NORMX BCC NORM ;IF EVEN,NORMALIZE PROD,ELSE COMP
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FCOMPL SEC ;SET CARRY FOR SUBTRACT. <--------------- not
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LDX #$3 ;INDEX FOR 3 BYTE SUBTRACT.
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COMPL1 LDA #$0 ;CLEAR A.
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SBC X1,X ;SUBTRACT BYTE OF EXP1.
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STA X1,X ;RESTORE IT.
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DEX ;NEXT MORE SIGNIFICANT BYTE.
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BNE COMPL1 ;LOOP UNTIL DONE.
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BEQ ADDEND ;NORMALIZE (OR SHIFT RT IF OVFL).
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FDIV JSR MD1 ;TAKE ABS VAL OF MANT1, MANT2. <--------- div
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SBC X1 ;SUBTRACT EXP1 FROM EXP2.
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JSR MD2 ;SAVE AS QUOTIENT EXP.
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DIV1 SEC ;SET CARRY FOR SUBTRACT.
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LDX #$2 ;INDEX FOR 3-BYTE SUBTRACTION.
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DIV2 LDA M2,X
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SBC E,X ;SUBTRACT A BYTE OF E FROM MANT2.
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PHA ;SAVE ON STACK.
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DEX ;NEXT MORE SIGNIFICANT BYTE.
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BPL DIV2 ;LOOP UNTIL DONE.
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LDX #$FD ;INDEX FOR 3-BYTE CONDITIONAL MOVE
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DIV3 PLA ;PULL BYTE OF DIFFERENCE OFF STACK
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BCC DIV4 ;IF M2<E THEN DON'T RESTORE M2.
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STA M2+3,X
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DIV4 INX ;NEXT LESS SIGNIFICANT BYTE.
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BNE DIV3 ;LOOP UNTIL DONE.
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ROL M1+2
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ROL M1+1 ;ROLL QUOTIENT LEFT, CARRY INTO LSB
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ROL M1
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ASL M2+2
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ROL M2+1 ;SHIFT DIVIDEND LEFT
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ROL M2
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BCS OVFL ;OVFL IS DUE TO UNNORMED DIVISOR
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DEY ;NEXT DIVIDE ITERATION.
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BNE DIV1 ;LOOP UNTIL DONE 23 ITERATIONS.
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BEQ MDEND ;NORM. QUOTIENT AND CORRECT SIGN.
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MD2 STX M1+2
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STX M1+1 ;CLEAR MANT1 (3 BYTES) FOR MUL/DIV.
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STX M1
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BCS OVCHK ;IF CALC. SET CARRY,CHECK FOR OVFL
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BMI MD3 ;IF NEG THEN NO UNDERFLOW.
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PLA ;POP ONE RETURN LEVEL.
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PLA
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BCC NORMX ;CLEAR X1 AND RETURN.
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MD3 EOR #$80 ;COMPLEMENT SIGN BIT OF EXPONENT.
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STA X1 ;STORE IT.
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LDY #$17 ;COUNT 24 MUL/23 DIV ITERATIONS.
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RTS ;RETURN.
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OVCHK BPL MD3 ;IF POSITIVE EXP THEN NO OVFL.
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OVFL JMP OVLOC
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* ORG $F63D
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FIX1 JSR RTAR
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FIX LDA X1 ; <------------------------------ fp to int
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BPL UNDFL
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CMP #$8E
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BNE FIX1
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BIT M1
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BPL FIXRTS
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LDA M1+2
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BEQ FIXRTS
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INC M1+1
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BNE FIXRTS
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INC M1
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FIXRTS RTS
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UNDFL LDA #$0
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STA M1
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STA M1+1
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RTS |