Russian Peasant Multiplication

From Assembly to Basic to Javascript.

Here are muy implementations of Russian Peasant Multiplication implemented in various languages:

6502 Assembly Language (Both ca65 and merlin32 sources)
Applesoft BASIC
JavaScript (Procedural version)
JavaScript (OOP version)

A .dsk image has been provided as an convenience.

To see how much faster the Assembly version is then the BASIC version:

RUN  RPM.BAS
BRUN RPM.BIN

And enter in 123456789 * 987654321 respectively for A and B ...

Version	Time
Applesoft	33 s
Assembly	~1 s

So what the heck is it?

An alternative algorithm to implement multiplication using only:

bit-shift (left and right), and
addition.

Example of "normal" multiplication:

In base 10:

In base 2:

        01010110  (86)
        00111001  (57)
        --------
        01010110  (86 * 2^0 =   86)
       00000000   (86 * 2^1 =  172)
      00000000    (86 * 2^2 =  344)
     01010110     (86 * 2^3 =  688)
    01010110      (86 * 2^4 = 1376)
   01010110       (86 * 2^5 = 2752)
  ==============
  01001100100110  (4902 = 86*2^0 + 86*2^3 + 86*2^4 + 86*2^5)

Example of Russian Peasant multiplication:

In Base 10:

               A         B   Sum     =    0
              86        57     0 + A =   86 (b is odd)
      x 2 =  172  / 2 = 28    86     =   86
      x 2 =  344  / 2 = 14    86     =   86
      x 2 =  688  / 2 =  7    86 + A =  774 (b is odd)
      x 2 = 1376  / 2 =  3   774 + A = 2150 (b is odd)
      x 2 = 2752  / 2 =  1  2150 + A = 4902 (b is odd)

In Base 2:

               A         B  Sum = 0
        01010110  00111001  + A = 00000001010110 (b is odd)
       010101100  00011100      = 00000001010110
      0101011000  00001110      = 00000001010110
     01010110000  00000111  + A = 00001100000110 (b is odd)
    010101100000  00000011  + A = 00100001100110 (b is odd)
   0101011000000  00000001  + A = 01001100100110 (b is odd)

2.1 KiB Raw Blame History

Russian Peasant Multiplication

So what the heck is it?

2.1 KiB

Raw Blame History