Computational Mathematics

1
Kate Ross
Mr. Bailey
Computational Mathematics
3 March 2016
The Function of the Summation of Two Integers Without Using Arithmetic Operators
The first thing that comes to mind is the processing of bits. Why? We have no choice – we
can not use the "+" operator. So let's sum the numbers as it is done by computers.
Now we need to figure out how the summation works. The additional tasks allow us to
develop new skills, learn something interesting, and create new templates.
So let's look at the additional task. We will use the decimal number system.
To sum 759 and 674, we fold the digit [0] of both numbers, transfer 1, and then turn to the
digit [1], transfer 1, etc. Similarly, we can work with the bits: sum all the digits and make transfers
if they are necessary.
Is it possible to simplify the algorithm? Yes! Let's say we want to divide the "sum" and
the "transfer." We have to do the following:
1. Perform the 759 + 674 operation, forgetting about the transfer. The result will be 323.
2. Perform the 759 + 674 operation, but only make transfers (without the summation of
digits). The result will be 1110.
3. Now we need to sum the results of the first two operations (using the same
mechanism described in steps 1 and 2): 1110 + 323 = 1433.
2
Now let’s go back to the binary system:
1. If we sum a pair of binary numbers, excluding the transfer of the sign, the i-th summed
bit can be zero only if the i-th bits of the a and b numbers coincide (both have a value
of 0 or 1). This is the classic operation XOR.
2. If we sum a pair of numbers, performing only the transfer, then the i-th bit of the sum
is set to 1 only if the (i-1)-th bits of both numbers (a and b) have a value of 1. This is
the AND operation with an offset.
3. We need to repeat these steps until there are no more transfers.
The following code implements this algorithm:
public static int summarize(int a, int b) {
if (b == 0) return a;
int sum = a ^ b; // sum without the transfer
int contain = (a & b) << 1; // transfer without the sum
return summarize(sum, contain); // recursion
}
The problems related to the implementation of basic operations (sum, subtraction) are quite
popular. To solve these problems, we need to deal with the way operations are usually
implemented, and then find a way that allows us to write code with the restrictions.
Thanks for your attention!
 


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