Modular Arithmetic and Primality
Modular Arithmetic and Primality
Modular Arithmetic and Primality
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⎧⎧ 2(x⋅ ⎣⎣y/2⎦⎦) if y is even<br />
x⋅ y = ⎨⎨<br />
⎩⎩ x + 2(x⋅ ⎣⎣y/2⎦⎦) if y is odd<br />
€<br />
Obvious equality, yet it gives us a divide <strong>and</strong> conquer<br />
opportunity since we halve the size at each step<br />
Prep us for <strong>Modular</strong> exponentiation which uses the same<br />
basic approach