• OhComeOn (unregistered)

    VERY literal Javascript implementation:

    russian_peasant_mult = function(left, right) {
      var lines, line, position, result = 0;
      left = parseInt(left); right = parseInt(right);
      if (isNaN(left) || isNaN(right)) {
        return NaN;
      }
      lines = [left + 'x' + right];
      while (!((line = lines[lines.length-1]).match(/^1x/))) {
        position = line.match(/[02468]x/) ? lines.length - 1 : lines.length;
        lines[position] = (Math.floor(line.split('x').shift() / 2)) + 'x' + (line.split('x').pop() * 2);
      }
      for (i = 0; i < lines.length; i++) {
        result += parseInt(lines[i].split('x').pop());
      }
      return result;  
    }
    
  • Bob Archer (unregistered)

    I'm a latecomer. Still fun to do.

    Code handles negative values OK.

    2 VB.Net ways:

    Way 1 - Recursive:

    Protected Sub RussianPeasantMultiplication(ByVal n1 As Integer, ByVal n2 As Integer, ByVal n3 As Integer)
        If Math.Abs(n1) >= 1 Then
            Console.WriteLine(n1 & " x " & n2)
            n3 = n3 + IIf(n1 Mod 2, Math.Abs(n2), 0) * IIf(n1 < 0, -1, 1) * IIf(n2 < 0, -1, 1)
            RussianPeasantMultiplication(Math.Floor(Math.Abs(n1 / 2)) * IIf(n1 < 0, -1, 1), n2 * 2, n3)
        Else
            Console.WriteLine("TOTAL: " & n3)
        End If
    End Sub
    

    Way 2 - While Loop:

    Protected Sub RussianPeasantMultiplication1(ByVal n1 As Integer, ByVal n2 As Integer)
        Dim RunningTotal As Integer = 0
        While (Math.Abs(n1))
            Console.WriteLine(n1 & " x " & n2)
            RunningTotal = RunningTotal + IIf(n1 Mod 2, Math.Abs(n2), 0) * IIf(n1 < 0, -1, 1) * IIf(n2 < 0, -1, 1)
            n1 = Math.Floor(Math.Abs(n1 / 2)) * IIf(n1 < 0, -1, 1)
            n2 = n2 * 2
        End While
        Console.WriteLine("TOTAL: " & RunningTotal)
    End Sub
    
  • Alex Elder (unregistered)

    unsigned int mu_ru(a, b) { unsigned int c = 0;

        while ((c += (a & 1) * (b <<= 1) >> 1) && (a >>= 1))
            ;
        return c;
    

    }

  • your mom (unregistered) in reply to mol1111
    package test;

    public class RussianPeasantMultiplication {

    public static void main(String[] args) {
        RussianPeasantMultiplication ruskie = new RussianPeasantMultiplication();
        ruskie.publish(18, 23);
        ruskie.publish(13, 13);
        ruskie.publish(15, 0);
        ruskie.publish(0, 15);
        ruskie.publish(-2, 2);
        ruskie.publish(2, -2);
    }
    
    private void publish(int a, int b) {
        System.out.println(a + " X " + b + " = " + multiply(a, b) + " "
                + m(a, b, 0));
    
    }
    
    public int multiply(int a, int b) {
        return recursiveMultiply(a, b, 0);
    }
    
    /**
     * Tail recursive Russian peasant multiplication
     */
    private int recursiveMultiply(int a, int b, int total) {
        if (Math.abs(a) >= 1) {
            if (a % 2 == 0) {
                return recursiveMultiply(a / 2, b * 2, total);
            } else {
                if (a < 0) {
                    return recursiveMultiply(a / 2, b * 2, total - b);
                } else {
                    return recursiveMultiply(a / 2, b * 2, total + b);
                }
            }
        } else {
            return total;
        }
    }
    
    /**
     * In Soviet Russia, tail recurse you.
     * 
     * @param a
     * @param b
     * @param t
     * @return a==0?t:a%2==0?m(a/2, b*2, t):m(a/2, b*2, a<0?t-b:t+b);
     */
    private int m(int a, int b, int t) {
        return a == 0 ? t : a % 2 == 0 ? m(a / 2, b * 2, t) : m(a / 2, b * 2,
                a < 0 ? t - b : t + b);
    }
    

    }

  • your mom (unregistered) in reply to your mom

    Java

  • JavaGuru (unregistered)

    public class Praxis {

    public static int multiply(int a, int b) { if(a < 0) { a *= -1; b *= -1; }

    int c = 0;
    while(a >= 1)
    {
    	if((a & 0x1) == 1) c += b;
    	a >>= 1;
    	b <<= 1;
    }
    return c;
    

    }

    public static void main(String[] args) { int a = Integer.parseInt(args[0]); int b = Integer.parseInt(args[1]); int c = multiply(a, b); System.out.println(a + " x " + b + " = " + c); }

    }

  • M (unregistered)

    Maude solution

    mod RUSSIAN is
      including NAT .
      sorts Obj .
      op <_,_,_> : Nat Nat Nat -> Obj .
      vars A B R : Nat .
      crl < A, B, R > => < A quo 2, B + B, R + if A rem 2 == 1 then B else 0 fi > if A > 0 . 
    endm
    
    rew < 18, 23, 0 > .
    
    rewrite in RUSSIAN : < 18,23,0 > .
    rewrites: 41 in 139000ms cpu (0ms real) (0 rewrites/second)
    result Obj: < 0,736,414 >
    
  • aMo (unregistered)

    int ru_mult(int a, int b) { int result = 0; do { if(a % 2) result += b; b <<= 1; } while(a >>= 1); return result; }

    i can't do it smaller + faster than that..

  • aMo (unregistered) in reply to Alex Elder

    this doesn't work for me..

  • (cs) in reply to egilhh

    I'm teaching myself Clojure, so I created a version of this in Clojure using sequence transformations:

    (defn peasant-step
      "Performs one step in the peasant multiplication algorithm, taking a 
      two-element vector as input, and returning a two-element vector"
      [[a b]]
      [(quot a 2) (* b 2)])
    
    (defn all-peasant-steps
      "For a given pair of numbers, returns all peasant multiplication steps"
      [a b]
      (for [s (iterate peasant-step [a b]) :while (#(not (zero? (first %))) s)] s))
    
    (defn odd-peasant-steps
      "Return all peasant steps where the first element is odd"
      [steps]
      (for [s steps :when (odd? (first s))] s))
    
    (defn peasant-multiply
      "Perform peasant multiplication on two numbers"
      [a b]
      (reduce + 
        (map second (odd-peasant-steps (all-peasant-steps a b)))))
    
  • Rodrigo Alfonso (unregistered)

    Kind of late but:

        private static int RussianMultiply(int firstNumber, int secondNumber)
        {
            if (firstNumber == 0 || secondNumber == 0)
                return 0;
            if (firstNumber == 1)
                return (secondNumber);
            return (RussianMultiply(firstNumber / 2, secondNumber * 2) + (firstNumber % 2 == 0 ? 0 : secondNumber));
        }
    
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  • anonymous (unregistered)

    #!usr/bin/perl6 -e

    Int $i; Int $j; Int @i; Int @j; $i = +(input());

    $j = +(input());

    while i != 1 { @i ,= $i; @j ,= $j; $i +>= 1; $j +<= 1; } @j = gather for @i Z @j -> $test, $result { take $result if $test % 2 } say([+] @j);

  • juli (unregistered)

    import java.io.DataInputStream; import java.io.IOException; public class PergjysmoShumezo {

    long k1=System.currentTimeMillis();
    /**
     * @param args
     */
    static boolean tek(int numer1)
    {
    	if ((numer1%2)!=0)
    	{
    		return true;
    	}
    	else
    	{
    		return false;
    	}
    }
    public static void main(String[] args) throws IOException
    {
    	//Numrat duhet te jene te plote
    	
    	int numer1;
    	int numer2;
    	int shuma=0;
    	DataInputStream in =new DataInputStream(System.in);
    	System.out.println("vendosni numrin1");
    	numer1=Integer.parseInt(in.readLine());
    	System.out.println("vendosni numrin2");
    	numer2=Integer.parseInt(in.readLine());
    	
    	//Numri i pare duhet te jete pozitiv
    	while(numer1>0)
    	{
    		if(tek(numer1))
    		{
    			shuma=shuma+numer2;
    		}
    		numer1=numer1/2;
    		numer2=numer2*2;
    	}
    	
    	System.out.println("vlera eshte:"+shuma);
    	
    
    }
    

    long k2=System.currentTimeMillis();

    { System.out.println("Koha e e ekzekutimit eshte k2-k1=" +(k2-k1)); } }

  • J (unregistered)
       bs =: 4 : '#.(#:x),y#0'
       rm =: 4 : '+/y bs"0 I.|.#:x'
       18 rm 23
    2304

    x is the left argument, y the right argument.

    x bs y: bitshift (x<<y) y#0 A list of y 0's. (#:x) The binary representation of x. , Join these together. #. Convert binary list to a number.

    x rm y: russian peasant multiplication. |.#:y Reverse binary of x (lowest bit first) I. Get indices of all 1's y bs"0 Bitshift each element in the list with y as left argument. +/ Sum.

  • Limao Luo (unregistered)
    public static long multiply(int a, int b) {
        long tot = 0;
        while (a > 0) {
            if ((a & 1) == 1)
                tot += b;
            a >>= 1;
            b <<= 1;
        }
        return tot;
    }
    

    captcha: "iusto" = I have gusto.

  • Anders (unregistered)

    function rpm(x,y){return x?rpm(x>>1,y+y)+y*(x&1):0}

    Very tweetable JavaScript indeed! :)

  • Adeel Zafar Soomro (unregistered)

    A solution in Factor programming language:

    : 2* ( x -- y )
        1 shift ; inline
    
    : rpm ( x y -- x*y )
        [ dup 0 > ]
        [ dup odd? [ over ] [ 0 ] if
          [ [ 2* ] [ 2/ ] bi* ] dip ]
        produce sum 2nip ;

    For integers, it produces the correct result so long as the second argument is non-negative.

  • Alexander Schneider (unregistered)

    I got a Clojure solution here. (I don't even know if the post is being still watched)

    (defn russian-mult
      "Multiplies two number the russian way. Na sdorowje!"
      [fnum snum]
      (loop [left fnum
             right snum
             sum 0]
        (if (= left 1)
          (+ sum right)
          (recur (quot left 2)
                 (* right 2)
                 (if (even? left) sum (+ sum right))))))
    
  • AI (unregistered)

    I wrote it in Befunge. Hopefully nothing was changed when I copied it...

    >&&v     >01g84*[email protected]
        >:0`!|
    >   ^    >:2%!v
                 v_\:01g+01p\v
                 >v          <
    ^       \*2\/2<
    ^  <

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