Appendix E

Binary Field Arithmetic

Binary field arithmetic is used in coding. The basic rules are very simple. Addition is as follows:

0+0=00+1=11+0=11+1=0

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This also corresponds to the exclusive OR or XOR operator in digital logic. Subtraction results are identical to addition; there is no distinction between the two operations.
Multiplication is as follows:

0·0=00·1=01·0=01·1=1

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Division is not defined or allowed.
Linearity means that if two input codewords are input to a system, X1 and X2, the output result is the same as if the sum of two codewords X1 + X2 were input instead. A more mathematical way to express this idea is as follows:

Y1=f(X1)Y2=f(X2)

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For a linear system

Y2+Y1=f(X2+X1)

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