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POMultiplication of 2 positive numbers giving a negative result
 

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  1. POMultiplication of 2 positive numbers giving a negative result
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    <blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/3001836/how-does-java-handle-integer-underflows-and-overflows-and-how-would-you-check-fo">How does Java handle integer underflows and overflows and how would you check for it?</a><br> <a href="https://stackoverflow.com/questions/6050796/multiplication-of-two-ints-gets-negativ">Multiplication of two int’s gets negativ</a> </p> </blockquote> <p>My program is an implementation of a bloom filter. However, when I'm storing my hash function results in the bit array, the function (of the <code>form f(i) = (a*i + b) % m</code> where a, b, i, m are all positive integers) is giving me a negative result. The problem seems to be in the calculation of a*i which is coming out to be negative.</p> <p>Ignore the print statements in the code; those were for debugging. Basically, the value of temp in this block of code is coming out to be negative and so I'm getting an <code>ArrayOutOfBoundsException</code>.</p> <p><code>m</code> is the bit array length, <code>z</code> is the number of hash functions being used, <code>S</code> is the set of values which are members of this bloom filter and <code>H</code> stores the values of a and b for the hash functions f1, f2, ..., fz.</p> <pre><code>public static int[] makeBitArray(int m, int z, ArrayList&lt;Integer&gt; S, int[] H) { int[] C = new int[m]; for (int i = 0; i &lt; z; i++) { for (int q = 0; q &lt; S.size() ; q++) { System.out.println(H[2*i]); int temp = S.get(q)*(H[2*i]); System.out.println(temp); System.out.println(S.get(q)); System.out.println(H[2*i + 1]); System.out.println(m); int t = ((H[2*i]*S.get(q)) + H[2*i + 1])%m; System.out.println(t); C[t] = 1; } } return C; } </code></pre>
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    1. CORelated: http://stackoverflow.com/questions/3001836, http://stackoverflow.com/questions/512266
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      1. POMultiplication of 2 positive numbers giving a negative result
      1. USTomasz Nurkiewicz
 

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