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    <p>Using precomputed lookup tables, it's possible to detect whether one player has five in a row in about 18 instructions. The following routine takes as input all stones of one player packed into a 64-bit int:</p> <pre><code>inline quadrant_t quadrant(uint64_t state, int q) { assert(0&lt;=q &amp;&amp; q&lt;4); return (state&gt;&gt;16*q)&amp;0xffff; } // Determine if one side has 5 in a row inline bool won(side_t side) { /* To test whether a position is a win for a given player, we note that * there are 3*4*2+4+4 = 32 different ways of getting 5 in a row on the * board. Thus, a 64-bit int can store a 2 bit field for each possible * method. We then precompute a lookup table mapping each quadrant state * to the number of win-possibilities it contributes to. 28 of the ways * of winning occur between two boards, and 4 occur between 4, so a sum * and a few bit twiddling checks are sufficient to test whether 5 in a * row exists. See helper for the precomputation code. */ uint64_t c = win_contributions[0][quadrant(side,0)] + win_contributions[1][quadrant(side,1)] + win_contributions[2][quadrant(side,2)] + win_contributions[3][quadrant(side,3)]; return c&amp;(c&gt;&gt;1)&amp;0x55 // The first four ways of winning require contributions from three quadrants || c&amp;(0xaaaaaaaaaaaaaaaa&lt;&lt;8); // The remaining 28 ways require contributions from only two } </code></pre> <p>The full source code is here:</p> <p><a href="https://github.com/girving/pentago/blob/9c9dedbb8dd3a5cf8dd778d28f351419126bbb7c/engine.cpp#L94" rel="nofollow">https://github.com/girving/pentago/blob/9c9dedbb8dd3a5cf8dd778d28f351419126bbb7c/engine.cpp#L94</a></p>
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    1. POWinners on a Pentago board
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