/* Object Orientated Version */
"use strict"; // Idiotic JavaScript design requires kludge for type safety

/*
To run from the command line:

    node rpm_oop [-v] [# [#]]

Legend:
   []  Paramater is optional
   -v  Turn on verbose output
   #   Number

Requires: node.js
*/

var LOG  = 0; // Verbose logging
var BASE = 10;

var defaultA = "86";
var defaultB = "57";


// --------------------------------------------------------------------------------

// BCD Type
var BCD = function( width, text )
{
    this.array = new Array( width );

    if (text !== undefined)
        this.Fill( text );
}

BCD.prototype = 
{
    constructor: BCD,

    /** lhs += rhs
      */
    // ========================================================================
    Add2: function( rhs )
    {
        var n     = this.array.length;
        var carry = 0;
        var sum   = 0;

        for( var i = 0; i < n; ++i )
        {
            sum   = this.array[i] + rhs.array[i] + carry;
            carry = (sum >= BASE) | 0;

            if (sum >= BASE)
                sum -= BASE;

            this.array[ i ] = sum;
        }
    },

    /** Print array BCD digits
      * Stored little endian: LSB[0] MSB[n]
      */
    // ========================================================================
    Dump: function( prefix )
    {
        var n    = this.array.length;
        var text = prefix ? prefix : "";

        for( var i = n - 1; i >= 0; --i )
            text += this.array[ i ];

        console.log( text );
    },

    /** Convert string to BCD array, aka, atoi()
        Remaining digits are zero filled
      * @param {Number[]} array
      * @param {String}   text
      */
    // ========================================================================
    Fill: function( text )
    {
        var i;
        var n = this.array.length;
        var m = text.length;
        var v;

        // Extra error checking would verify m > n

        // Set all digits from string -- set in reverse order
        for( i = 0; i < m; ++i )
            this.array[ (m-1) - i ] = text.charCodeAt( i ) - 48;

        // Set remaining digits to zero
        for( ; i < n; ++i )
            this.array[ i ] = 0;
    },

    // ========================================================================
    isOdd: function()
    {
        return this.array[0] & 1 ? true : false;
    },

    // ========================================================================
    isZero: function( )
    {
        var i;
        var n    = this.array.length;
        var zero = true; // default to all zeroes until we find otherwise

        for( i = 0; i < n; ++i )
            zero &= (this.array[i] == 0);

        return zero;
    },

    // Print array digits in reverse
    // ========================================================================
    Print: function( prefix )
    {
        var i;
        var n    = this.array.length;
        var text = prefix ? prefix : "";
        var zero = true; // assume leading zero -> skip digit

        for( i = n - 1; i >= 0; --i )
        {
            zero &= (this.array[ i ] == 0);
            if( !zero )
                text += this.array[ i ];
        }

        console.log( text );
    },

    // ========================================================================
    Shl1: function()
    {
        var i;
        var n     = this.array.length;
        var carry = 0;
        var sum   = 0;

        for( i = 0; i < n; ++i )
        {
            sum   = this.array[ i ]*2 + carry;
            carry = (sum >= BASE) | 0;

            if (sum >= BASE)
                sum -= BASE;

            this.array[ i ] = sum;
        }
    },

    // ========================================================================
    Shr1: function()
    {
        var i;
        var n     = this.array.length;
        var carry = 0;
        var q     = 0;
        var div   = 0;
        var rem   = 0;

        for( i = n-1; i >= 0; --i )
        {
            div           = this.array[ i ] + carry; // dividend
            q             = (div / 2) | 0; // 2 is divisor
            this.array[i] = q;
            rem           = div - q*2; // 2 is divisor
            carry         = rem * BASE;
        }
    }
};


// --------------------------------------------------------------------------------


/** Russian Peasant Multiplication with native integers
  * @param {Number} a
  * @param {Number} b
  */
// ========================================================================
function RPM( x, y )
{
    var a   = x; // Javascript has no native unsigned 32-bit nor 64-bit integers
    var b   = y; // ctypes.UInt64() is only Firefox "extension"
    var sum = 0;

    while( b )
    {
        if (b & 1)
            sum += a;

if(LOG) console.log( "A: " + a + ", B: " + b + ", Sum: " + sum );
        if (a < 0)
            return console.log( "ERROR: 31-bit integer overflow. Number too large after shifting left: " + x );

        a <<= 1;
        b >>= 1;
    }

    console.log( x + " x " + y + " = " + sum );
}


/** Russian Peasant Multiplication with strings
  * @param {String} a
  * @param {String} b
  */
// ========================================================================
function RPM_String( a, b )
{
    var n = a.length; // i.e. 32-bit,                     e.g. 999
    var m = b.length; // i.e. 32-bit                      e.g. 999
    var s = n + m   ; // i.e  32-bit * 32b-bit = 64-bit   e.g. 998001

    var digitsA = new BCD( s,  a  );
    var digitsB = new BCD( s,  b  );
    var digitsS = new BCD( s, "0" );

    while( true )
    {
        var done = digitsB.isZero();
        if( done )
            break;

        var odd = digitsB.isOdd();
        if( odd )
            digitsS.Add2( digitsA ); // S += A

if(LOG) digitsA.Dump( " A =  " );
        digitsA.Shl1();
if(LOG) digitsA.Dump( " A << " );
if(LOG) digitsB.Dump( " B =  " );
        digitsB.Shr1();
if(LOG) digitsB.Dump( " B >> " );
if(LOG) digitsS.Dump( "Sum:  " );
    }
    digitsS.Print();
}


// ========================================================================
function main()
{
    var args  = process.argv.slice( process.execArgv.length + 2 );
    var param = 0;

    if (args[0] === '-v')
    {
        LOG = 1;
        param++; // skip switches to first paramater
    }

    var params = [];
    params.push( (args[param+0] === undefined) ? defaultA : args[param+0] );
    params.push( (args[param+1] === undefined) ? defaultB : args[param+1] );

    console.log( "= Integer = " );
    RPM( params[0] | 0, params[1] | 0);
    console.log( "\n" );

    console.log( "= BCD String =" );
    RPM_String( params[0], params[1] );
    console.log( "\n" );
}

main();