Radix Complement

Radix Complement Representation:

In the decimal number system, the radix complement is the 10’s complement. In radix complement representation system, the complement of an n-digit number is obtained by subtracting the number from 10n.

Let us consider some examples of 3-digit numbers and their radix complement in decimal system.

Decimal Number





Radix Complement





From the above discussion we find that a subtraction operation is to be preformed to get the 10’s complement of a number, say, N. This subtraction operation can be avoided by rewriting 10n as (10n - 1) + 1 and 10n - N as {(10n - 1) - N} + 1. The number 10n - 1 is of the form 999...99 consisting of n digits. If the complement of a digit be defined as (9 - the concerned digit), then (10n - 1) - N is obtained by complementing the digits of N.

Therefore, the 10’s complement of the number N is obtained by subtracting each digit of the number from 9 and then adding 1 to the LSD of the number so formed.

For instance, the 10’s complement of 172 is (827 + 1) or 828 and that of 405 is (594 + 1) or 595.

For the binary number system the radix complement is the two’s complement. The 2’s complement of a binary number is obtained by subtracting each bit of the number from the radix diminished by 1 i.e. from (2 - 1) or 1 and adding an 1 to the LSB. The application of this rule is very simple. We have to just change 1 to 0 and 0 to 1 in every bit and then add 1 to the LSB of the number so formed. For example, the 2’s complement of the binary number 11011 is (00100 + 1) or 00101 and that of 10110 is (01001 + 1) or 01010.

If the number be in signed magnitude representation, it is positive if the MSB is 0 and negative if the MSB is 1. The decimal equivalent of a 2’s complement binary number, in the case of signed-magnitude representation, is computed in the same way as for an unsigned number except that the weight of the MSB is -2n-1 instead of +2n-1 for an n-bit binary number.

Let us observe some examples of 8-bit binary numbers and their 2’s complement are shown below:

Binary Number

Sign bit         01101101

Complement:  10010010

                            + 1


Decimal equivalent

+ 109

- 128 + 19 = -109

Binary Numbers

  • Number System

  • Decimal Number System

  • Why Binary Numbers are Used

  • Binary to Decimal Conversion

  • Conversion of Numbers

  • Hexa-decimal Number System

  • Conversion of Binary Numbers to Octal or Hexa-decimal Numbers

  • Octal and Hexa-Decimal Numbers

  • Signed-magnitude Representation

  • Radix Complement

  • Diminished Radix Complement

  • Arithmetic Operations of Binary Numbers

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