I was using the 24 bit adder from
http://www.piclist.com/techref/default.asp?from=/techref/microchip/math/&url
=add/24b.htm

and one of my problems was there's a bug in the code.  The middle byte
references the LS byte
again instead of the middle byte.  Once I changed the 2  LS byte references
in that section to Middle byte references R1L -->  R1M    the program
finally gave me the output I calculated by hand.  Otherwise, my actual
addition problem I had was due to my error in conversion between variable
names, trying to rewrite it to fit my own program syntax, and trying to copy
the result into a separate 24 bit variable instead of destroying one of the
2 input numbers...I think I have it figured out now.

Multiplication,  where I get 2 x 1 = something way too big, I am trying to
use this program which I must have pulled from one of the sites previously
referenced in the list.  I don't know much about the theory of rotating bits
to multiply so I can't debug it, I can only see that it gives the wrong
output and then hope to find another working routine or have someone tell me
it should or shouldn't work and maybe I'm doing something wrong again.  I
assume the variables in this code are  result = Product,   input numbers 1
and 2 = Multiplier, Multiplicand:

Mul16 clrf   Product
        clrf   Product+1
        movlw  16               ;Operating on 16 Bits
        movwf  BitCount
        Loop                    ;Loop Here for Each Bit

        rrf    Multiplier+1     ;Shift the Multiplier down
        rrf    Multiplier       ;by one
        btfss  STATUS,C         ;If the bit is set, add
        goto   Skip             ;the Multiplicand to the
                                ;"Product"
        movf   Multiplicand+1
        addwf  Product+1
        movf   Multiplicand
        addwf  Product
        btfsc  STATUS,C
        incf   Product+1

        Skip                    ;Shift up Multiplicand and
        bcf    STATUS,C         ;Loop Around
        rlf    Multiplicand
        rlf    Multiplicand+1

        decfsz BitCount
        goto  Loop
 return