Apple-2-SW/apple2_russian_peasant_multiplication
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Procedural Javascript

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Michael Pohoreski 2016-08-17 14:22:55 -07:00
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/* Procedural Version */
"use strict"; // Idiotic JavaScript design requires kludge for type safety
/*
To run from the command line:
node rpm_proc [-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 Utility Functions
/** lhs += rhs
*/
// ========================================================================
function Add2( lhs, rhs )
{
var n = lhs.length;
var carry = 0;
var sum = 0;
for( var i = 0; i < n; ++i )
{
sum = lhs[i] + rhs[i] + carry;
carry = (sum >= BASE) | 0;
if (sum >= BASE)
sum -= BASE;
lhs[ i ] = sum;
}
}
/** Print array BCD digits
* Stored little endian: LSB[0] MSB[n]
*/
// ========================================================================
function Dump( array, prefix )
{
var n = array.length;
var text = prefix ? prefix : "";
for( var i = n - 1; i >= 0; --i )
text += array[ i ];
console.log( text );
}
/** Convert string to BCD array, aka, atoi()
Remaining digits are zero filled
* @param {Number[]} array
* @param {String} text
*/
// ========================================================================
function Fill( array, text )
{
var i;
var n = 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 )
array[ (m-1) - i ] = text.charCodeAt( i ) - 48;
// Set remaining digits to zero
for( ; i < n; ++i )
array[ i ] = 0;
}
// ========================================================================
function isOdd( array )
{
return array[0] & 1 ? true : false;
}
// ========================================================================
function isZero( array )
{
var i;
var n = array.length;
var zero = true; // default to all zeroes until we find otherwise
for( i = 0; i < n; ++i )
zero &= (array[i] == 0);
return zero;
}
// Print array digits in reverse
// ========================================================================
function Print( array, prefix )
{
var i;
var n = array.length;
var text = prefix ? prefix : "";
var zero = true; // assume leading zero -> skip digit
for( i = n - 1; i >= 0; --i )
{
zero &= (array[ i ] == 0);
if( !zero )
text += array[ i ];
}
console.log( text );
}
// ========================================================================
function Shl1( array )
{
var i;
var n = array.length;
var carry = 0;
var sum = 0;
for( i = 0; i < n; ++i )
{
sum = array[ i ]*2 + carry;
carry = (sum >= BASE) | 0;
if (sum >= BASE)
sum -= BASE;
array[ i ] = sum;
}
}
// ========================================================================
function Shr1( array )
{
var i;
var n = array.length;
var carry = 0;
var q = 0;
var div = 0;
var rem = 0;
for( i = n-1; i >= 0; --i )
{
div = array[ i ] + carry; // dividend
q = (div / 2) | 0; // 2 is divisor
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 Array( s );
var digitsB = new Array( s );
var digitsS = new Array( s );
Fill( digitsA, a );
Fill( digitsB, b );
Fill( digitsS, "0" );
while( true )
{
var done = isZero( digitsB );
if( done )
break;
var odd = isOdd( digitsB );
if( odd )
Add2( digitsS, digitsA ); // S += A
if(LOG) Dump( digitsA, " A = " );
Shl1( digitsA ); // A <<= 1
if(LOG) Dump( digitsA, " A << " );
if(LOG) Dump( digitsB, " B = " );
Shr1( digitsB ); // B >>= 1
if(LOG) Dump( digitsB, " B >> " );
if(LOG) Dump( digitsS, "Sum: " );
}
Print( digitsS );
}
// ========================================================================
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();