Multiply two numbers without using the "*" operator and bitwise operations

Question

How will you multiply two numbers without using the "*" and bitwise operations in an efficient way?(Just by using operators like +,-,/).

Take a look at http://stackoverflow.com/questions/2069488/how-can-i-perform-multiplication-without-the-operator — David, Apr 10 '13 at 09:53

score 1 · Answer 1 · answered Apr 10 '13 at 09:56

1

a*b == 10^(Log(a*b)) == 10^(Log(a) + Log(b)) == exp(ln(a) + ln(b))

where ^ means exponentiation and Log is the logarithm with a base of 10

answered Apr 10 '13 at 09:56

halex

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exp(ln(a) + ln(b)) then, not using a generic exponentiation – unkulunkulu Apr 10 '13 at 09:58
@unkulunkulu Thx. Added it as another transformation – halex Apr 10 '13 at 09:59

score 0 · Answer 2 · answered Apr 10 '13 at 09:59

multiply(a,b):
      if(a==0) return 0
      r<-0
      while(b/a!=r) r++
      return r

Ok, I'm kidding, but you should give more informations about your search: what is an efficient way for you? Can you give an approximation of the complexity searched? Or do you want the most efficient algorithm? Because, if you don't precise anything, I can answer too:

multiply(a,b):
      r<-0
      while(a!=0)
           r<-r+b
           b<-b-1
      return r

What's the point of the first code sample (which seems to do division)? — Bernhard Barker, Apr 10 '13 at 10:02

Multiply two numbers without using the "*" operator and bitwise operations

2 Answers2