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ADDITION USING 1’S COMPLIMENT

ADDITION USING 1’S COMPLIMENT

There are three different cases possible when we add two binary numbers which are as follows:

Case 1: Addition of the positive number with a negative number when the positive number has a greater magnitude.

Initially, calculate the 1’s complement of the given negative number. Sum up with the given positive number. If we get the end-around carry 1, it gets added to the LSB.

Example: 1101 and -1001

  1. First, find the 1’s complement of the negative number 1001. So, for finding 1’s complement, change all 0 to 1 and all 1 to 0. The 1’s complement of the number 1001 is 0110.

  2. Now, add both the numbers, i.e., 1101 and 0110;

    1101+0110=1 0011

  3. By adding both numbers, we get the end-around carry 1. We add this end around carry to the LSB of 0011.

    0011+1=0100

Case 2: Adding a positive value with a negative value in case the negative number has a higher magnitude.

Initially, calculate the 1’s complement of the negative value. Sum it with a positive number. In this case, we did not get the end-around carry. So, take the 1’s complement of the result to get the final result.

Example: 1101 and -1110

  1. First find the 1’s complement of the negative number 1110. So, for finding 1’s complement, we change all 0 to 1, and all 1 to 0. 1’s complement of the number 1110 is 0001.

  2. Now, add both the numbers, i.e., 1101 and 0001;

    1101+0001= 1110

  3. Now, find the 1’s complement of the result 1110 that is the final result. So, the 1’s complement of the result 1110 is 0001, and we add a negative sign before the number so that we can identify that it is a negative number.

Case 3: Addition of two negative numbers

Example: -1101 and -1110 in five-bit register

  1. Firstly find the 1’s complement of the negative numbers 01101 and 01110. So, for finding 1’s complement, we change all 0 to 1, and all 1 to 0. 1’s complement of the number 01110 is 10001, and 01101 is 10010.

  2. Now, we add both the complement numbers, i.e., 10001 and 10010;

    10001+10010= 1 00011

  3. By adding both numbers, we get the end-around carry 1. We add this end-around carry to the LSB of 00011.

    00011+1=00100

  4. Now, find the 1’s complement of the result 00100 that is the final answer. So, the 1’s complement of the result 00100 is 110111, and add a negative sign before the number so that we can identify that it is a negative number.