/*---- Assumes both HugeIntegers are positive and this > that -----------------*/
public HugeInteger subtract(HugeInteger that) {
if (this.compareTo(that) < 0) return that.subtract(this);
HugeInteger result = new HugeInteger(this.size());
int borrow = 0;
int difference;
int position = 0;
for (; position < that.size(); position++) {
difference = this.digitAt(position) - that.digitAt(position) - borrow;
if (difference < 0) {
difference += 10;
borrow = 1;
} else {
borrow = 0;
}
result.addDigit(difference);
DIGIT_OPERATIONS++;
}
for (; position < this.size(); position++) {
difference = this.digitAt(position) - borrow;
if (difference < 0) {
difference += 10;
borrow = 1;
} else {
borrow = 0;
}
result.addDigit(difference);
DIGIT_OPERATIONS++;
}
result.removeLeadingZeroes();
return result;
}
/*---- returns the sum of this and the provided HugeInteger -------------------*/
public HugeInteger add(HugeInteger that) {
this.removeLeadingZeroes();
that.removeLeadingZeroes();
HugeInteger result = new HugeInteger(max(this.size(), that.size()));
int carry = 0;
int position = 0;
int sum;
while (position < min(this.size(), that.size())) {
sum = this.digitAt(position) + that.digitAt(position) + carry;
if (sum >= 10) {
sum -= 10;
carry = 1;
} else {
carry = 0;
}
result.addDigit(sum);
position++;
DIGIT_OPERATIONS++;
}
if (this.size() > that.size()) {
while (position < this.size()) {
result.addDigit(this.digitAt(position) + carry);
carry = 0;
position++;
DIGIT_OPERATIONS++;
}
} else if (that.size() > this.size()) {
while (position < that.size()) {
result.addDigit(that.digitAt(position) + carry);
carry = 0;
position++;
DIGIT_OPERATIONS++;
}
}
if (carry == 1) {
result.addDigit(1);
}
return result;
}
/*---- multiplies this and the specified HugeInteger using "school" algorithm -*/
public HugeInteger multiply(HugeInteger that) {
// create zero-filled HugeInteger
int resultSize = this.size() + that.size();
ArrayList<Integer> list = new ArrayList<Integer>(Collections.nCopies(resultSize, 0));
HugeInteger result = new HugeInteger(list);
int carry = 0;
int m;
for (int i = 0; i < that.size(); i++) {
for (int j = 0; j < this.size(); j++) {
m = this.digitAt(j) * that.digitAt(i);
m = m + carry + result.digitAt(i + j);
result.setDigit(i + j, m % 10);
carry = m / 10;
DIGIT_OPERATIONS += 3; // three digit operations: two add, one multiply
}
if (carry > 0) {
result.setDigit(i + this.size(), result.digitAt(i + this.size()) + carry);
carry = 0;
}
}
result.removeLeadingZeroes();
return result;
}
/*---- compares this HugeInteger to provided HugeInteger for order ------------*/
public int compareTo(HugeInteger that) {
if (this == that) return 0;
else if (this.size() > that.size()) {
return 1;
} else if (this.size() < that.size()) {
return -1;
} else {
for (int i = this.size() - 1; i >= 0; i--) {
int thisDigit = this.digitAt(i);
int thatDigit = that.digitAt(i);
DIGIT_OPERATIONS++;
if (thisDigit > thatDigit) return 1;
else if (thisDigit < thatDigit) return -1;
}
return 0;
}
}