/*---- 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 a copy of the digits of this from provided integer to size()-1 -*/
public HugeInteger lowerCopy(int midPoint) {
HugeInteger result = new HugeInteger(midPoint);
for (int i = 0; i < midPoint; i++) {
result.addDigit(this.digitAt(i));
}
// 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;
}
/*---- returns a copy of this shifted to the left by the specified amount -----*/
public HugeInteger shift(int distance) {
HugeInteger result = new HugeInteger(this.size() + distance);
for (int i = 0; i < distance; i++) result.addDigit(0);
for (int i = 0; i < this.size(); i++) result.addDigit(this.digitAt(i));
return result;
}