Byron,

Thank you for your code. I tried to run it, but I am having certain
problems. Take for example,
the following problem, in 2s complement.

The following variable declerations are used:

TWOFOUR2 B'00001000'  Equivalent: c0=534035 (dec)
TWOFOUR1 B'00100110'
TWOFOUR0 B'00010011'

MULTIPLIER B'00000111'  Equivalent: u0=7 (dec)

Result: (MPLAB)

PROD2        B'00001000'   Equivalent: c0u0 (dec)
PROD1        B'00100110'
PROD0      B'00010011'

This does not seem to be the correct answer.

Any ideas on where the error could possibly be, or is it just me getting
confused with 2's comp...?

Thanks in advance for your help.

Regards,

Saurabh
======================================================CODE
USED================================

mult24x8:
        clrf    prod0           ; Clear the product
        clrf    prod1
        clrf    prod2
        clrf    prod3
        clrf    twofour3        ; Clear the top byte of the multiplicand
return

multloop:
        movf    mulitiplier,W   ; Check to see if eight bit is empty
        btfsc   STATUS,Z        ; Done if zero
        return
        bcf     STATUS,C        ; clear carry
        rrf     mulitiplier,F   ; Get the next bit
        btfss   STATUS,C        ; Add if carry is set
        goto    multshift       ; shift only if 0
        movf    twofour0,W      ; Add the 32 bits of multiplicand to product
        addwf   prod0,F         ; each addwf sets the carry
        btfsc   STATUS,C        ; Don't increment if no carry
        incf    prod1,F         ; Add one to next byte if carry occured
        movf    twofour1,W      ;
        addwf   prod1,F         ;
        btfsc   STATUS,C        ; Don't increment if no carry
        incf    prod2,F         ; Add one to next byte if carry occured
        movf    twofour2,W      ;
        addwf   prod2,F         ;
        btfsc   STATUS,C        ; Don't increment if no carry
        incf    prod3,F         ; Add one to next byte if carry occured
        movf    twofour3,W      ;
        addwf   prod3,F         ;

multshift:
        bcf     STATUS,C        ; clear carry
        rlf     twofour0,F      ; Shift the 24 bits one bit to the left
        rlf     twofour1,F
        rlf     twofour2,F
        rlf     twofour3,F
 return
return