Long multiplication: Difference between revisions

With integer inputs at this scale, JavaScript still gives a slightly lossy result, despite the subsequent digit by digit string concatenation approach.

var a1 = num1.toString().split("").reverse();

var a2 = num2.toString().split("").reverse();

var aResult = new Array;

for ( var iterNum1 = 0; iterNum1 < a1.length; iterNum1++ ) {

for ( var iterNum2 = 0; iterNum2 < a2.length; iterNum2++ ) {

var idxIter = iterNum1 + iterNum2; // Get the current array position.

aResult[idxIter] = a1[iterNum1] * a2[iterNum2] + ( idxIter >= aResult.length ? 0 : aResult[idxIter] );

if ( aResult[idxIter] > 9 ) { // Carrying

aResult[idxIter + 1] = Math.floor( aResult[idxIter] / 10 ) + ( idxIter + 1 >= aResult.length ? 0 : aResult[idxIter + 1] );

aResult[idxIter] -= Math.floor( aResult[idxIter] / 10 ) * 10;

}

}

}

return aResult.reverse().join("");

}

mult(Math.pow(2,64), Math.pow(2,64))</lang>

{{Out}}

<pre>340282366920938477630474056040704000000</pre>

Compare this with the full precision result:

<pre>340282366920938463463374607431768211456</pre>