Long multiplication: Difference between revisions

=={{Header|Ceylon}}==

<lang Ceylon>"run() is the main function of this module."

shared void run() {

function multiply(String|Integer|Integer[] top, String|Integer|Integer[] bottom, Integer base = 10) {

function fromString(String s) =>

s

.filter(not(','.equals))

.map((char) => Integer.parse(char.string))

.narrow<Integer>()

.sequence()

.reversed;

function toString(Integer[] ints) =>

""

.join(ints.interpose(',', 3).sequence().reversed)

.removeInitial("0")

.removeInitial(",");

function fromInteger(Integer int) => fromString(int.string);

function convertArg(String|Integer|Integer[] arg) =>

switch(arg)

case (is String) fromString(arg)

case (is Integer) fromInteger(arg)

case (is Integer[]) arg;

value a = convertArg(top);

value b = convertArg(bottom);

value p = a.size;

value q = b.size;

value product = Array.ofSize(p + q, 0);

for (bIndex->bDigit in b.indexed) {

variable value carry = 0;

for (aIndex->aDigit in a.indexed) {

assert (exists prodDigit = product[aIndex + bIndex]);

value temp = prodDigit + carry + aDigit * bDigit;

carry = temp / base;

product[aIndex + bIndex] = temp % base;

}

assert (exists lastDigit = product[bIndex + p]);

product[bIndex + p] = lastDigit + carry;

}

return toString(product.sequence());

}

value twoToThe64th = "18,446,744,073,709,551,616";

value expectedResult = "340,282,366,920,938,463,463,374,607,431,768,211,456";

value result = multiply(twoToThe64th, twoToThe64th);

print("The expected result is ``expectedResult`` and the real result was ``result``");

print("Do the match? ``expectedResult == result then "Yes!" else "No!"``");

}</lang>