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Length: 3584 (0xe00)
Types: TextFile
Names: »MPBMUL.MAC«
└─⟦01b5c9619⟧ Bits:30005906 Microsoft Multiplan v1.05 og HELP
└─ ⟦this⟧ »MPBMUL.MAC«
aseg org 200h .z80 ; ; ; Title Multiple-Precision Binary Multiplication ; Name: MPBMUL ; ; ; Purpose: Multiply 2 arrays of binary bytes ; Multiplicand = multiplicand * multiplier ; ; Entry: Register pair HL = Base address of multiplicand ; Register pair DE = Base address of multiplier ; Register B = Lenght of the arrays ; ; The arrays are unsigned binary numbers with a ; maximum lenght of 255 bytes, ARRAYÆ0Å is the ; least significant byte, and ARRAYÆLENGH-1Å ; the most significand byte. ; ; Exit: Multiplicand := multiplicand * multiplier ; ; Registers used: AF,BC,DE,HL ; ; Time: Assuming the average number of 1 bits in multi- ; plicand is 4 * lenght, then the time is approxi- ; mately ; (728 * lengh ^2) + (883 * lenght) + 300 cycles ; ; Size: Program 104 bytes ; Data 261 bytes ; ; ; MPBMUL: ;Exit if lenght is zero ld a,b and a ;Is the lenght of arrays = 0 ? ret z ;Yes, exit ;Make pointers point to end of operands ld c,b ;BC = lenght ld b,0 add hl,bc ;End = base + lenght ex de,hl ;DE points to end of multiplicand ld (mlier),hl ;save address of multiplier ld hl,hiprod add hl,bc ld (endhp),hl ;Save address at end of hiprod ;Set count to number of bits in array plus 1 ; count *= (lengh*8) + 1 ld l,c ;Move lenght to HL ld h,b add hl,hl ;Lenght * 8, shift left 3 times add hl,hl add hl,hl inc hl ;add 1 ld (count),hl ;Save number of bits to do ;Zero high product array zeropd: ld b,c ;B = lenght in bytes ld hl,hiprod ;Get address of hiprod zerolp: ld (hl),0 ;Store 0 inc hl djnz zerolp ;Continue until hiprod array is zero ;Multiply using the shit and add algorithm and a ;Clear carry first time through loop: ;Shift carry into hiprod array and least significant ; bit of hiprod to carry ld b,c ;Get lenght in bytes ld hl,(endhp) ;Get last byte of hiprod + 1 srplp: dec hl ;Back up to next byte rr (hl) djnz srplp ;Continue until index = 0 ;Shift carry (next bit of lower product) into most ; significant bit of multiplicand. ; this also shifts next bit of multiplicand to carry ld l,e ;HL = address of end of multipliand ld h,d ld b,c ;B = lenght in bytes sra1lp: dec hl ;Back up to next byte rr (hl) djnz sra1lp ;Continue until done ;If next bit of multiplicandd is 1 then ; add multiplier to hiprod array jp nc,deccnt ;Jump if next bit is zero ;Add multiplier to hiprod push de ;Save address of multiplicand ld de,(mlier) ;DE = address of multiplier ld hl,hiprod ;HL = address of hiprod ld b,c ;B = lenght in bytes and a ;Clear carry addlp: ld a,(de) ;Get next multiplier byte adc a,(hl) ;Add to hiprod ld (hl),a ;Store new hiprod inc de inc hl djnz addlp ;Continue until done pop de ;estore address of multiplicand ;Decrement bit counter, exit if done ; does not change carry deccnt: ld a,(count) dec a ld (count),a jp nz,loop ;Branch if lsb of count not zero push af ;Save carry ld a,(count+1) ;Get high byte of count and a ; is it zero ? jr z,exit ; exit if so dec a ;Decrement high byte of count ld (count+1),a pop af ;restore carry jp loop ;Continue exit: pop af ;Drop psw from stack ret ;Return ;DATA count: ds 2 ;Temporary for loop counter endhp: ds 2 ;Address of last byte of hiprod + 1 mlier: ds 2 ;Address of multiplier hiprod: ds 255 ;High product buffer «eof»