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    copied!<p>Upon closer look, your code looks correct to me; which makes one wonder whether the original authors had an off-by-one bug. I guess someone ought to look at how OpenCV implements it!</p> <p>Nonetheless, one suggestion to make it easier to understand is to flip the order of the <em>for</em> loops by going over all sizes first, then looping over the possible locations given the size:</p> <pre><code>#include &lt;stdio.h&gt; int main() { int i, x, y, sizeX, sizeY, width, height, count, c; /* All five shape types */ const int features = 5; const int feature[][2] = {{2,1}, {1,2}, {3,1}, {1,3}, {2,2}}; const int frameSize = 24; count = 0; /* Each shape */ for (i = 0; i &lt; features; i++) { sizeX = feature[i][0]; sizeY = feature[i][1]; printf("%dx%d shapes:\n", sizeX, sizeY); /* each size (multiples of basic shapes) */ for (width = sizeX; width &lt;= frameSize; width+=sizeX) { for (height = sizeY; height &lt;= frameSize; height+=sizeY) { printf("\tsize: %dx%d =&gt; ", width, height); c=count; /* each possible position given size */ for (x = 0; x &lt;= frameSize-width; x++) { for (y = 0; y &lt;= frameSize-height; y++) { count++; } } printf("count: %d\n", count-c); } } } printf("%d\n", count); return 0; } </code></pre> <p>with the same results as the previous <code>162336</code></p> <hr> <p>To verify it, I tested the case of a 4x4 window and manually checked all cases (easy to count since 1x2/2x1 and 1x3/3x1 shapes are the same only 90 degrees rotated):</p> <pre><code>2x1 shapes: size: 2x1 =&gt; count: 12 size: 2x2 =&gt; count: 9 size: 2x3 =&gt; count: 6 size: 2x4 =&gt; count: 3 size: 4x1 =&gt; count: 4 size: 4x2 =&gt; count: 3 size: 4x3 =&gt; count: 2 size: 4x4 =&gt; count: 1 1x2 shapes: size: 1x2 =&gt; count: 12 +-----------------------+ size: 1x4 =&gt; count: 4 | | | | | size: 2x2 =&gt; count: 9 | | | | | size: 2x4 =&gt; count: 3 +-----+-----+-----+-----+ size: 3x2 =&gt; count: 6 | | | | | size: 3x4 =&gt; count: 2 | | | | | size: 4x2 =&gt; count: 3 +-----+-----+-----+-----+ size: 4x4 =&gt; count: 1 | | | | | 3x1 shapes: | | | | | size: 3x1 =&gt; count: 8 +-----+-----+-----+-----+ size: 3x2 =&gt; count: 6 | | | | | size: 3x3 =&gt; count: 4 | | | | | size: 3x4 =&gt; count: 2 +-----------------------+ 1x3 shapes: size: 1x3 =&gt; count: 8 Total Count = 136 size: 2x3 =&gt; count: 6 size: 3x3 =&gt; count: 4 size: 4x3 =&gt; count: 2 2x2 shapes: size: 2x2 =&gt; count: 9 size: 2x4 =&gt; count: 3 size: 4x2 =&gt; count: 3 size: 4x4 =&gt; count: 1 </code></pre>
 

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