algorithm to simulate multiplication by addition

Question

How to design an algorithm to simulate multiplication by addition. input two integers. they may be zero, positive or negative..

Solution 1

def multiply(a, b):                                                                                                                                                               
    if (a == 1):
        return b
    elif (a == 0):
        return 0
    elif (a < 0):
        return -multiply(-a, b)
    else:
        return b + multiply(a - 1, b)

Solution 2

some pseudocode:

function multiply(x, y)
  if abs(x) = x and abs(y) = y or abs(x) <> x and abs(y) <> y then sign = 'plus'
  if abs(x) = x and abs(y) <> y or abs(x) <> x and abs(y) = y then sign = 'minus'

 res = 0
 for i = 0 to abs(y)
  res = res + abs(x)
 end

 if sign = 'plus' return res
    else return -1 * res

end function

Solution 3

val:= 0
bothNegative:=false

if(input1 < 0) && if(input2 < 0)
  bothNegative=true
if(bothNegative)
  smaller_number:=absolute_value_of(smaller_number)
for [i:=absolute_value_of(bigger_number);i!=0;i--]
do val+=smaller_number

return val;