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This is an automatically generated e-mail. To reply, visit:
<a href="http://reviewboard.kde.org/r/4992/">http://reviewboard.kde.org/r/4992/</a>
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<p style="margin-top: 0;">On August 12th, 2010, 7:17 p.m., <b>Ingo Klöcker</b> wrote:</p>
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<a href="/r/4992/diff/3/?file=33700#file33700line39" style="color: black; font-weight: bold; text-decoration: underline;">trunk/KDE/kdelibs/kdecore/util/krandom.h</a>
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(Diff revision 3)
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<td colspan="4"><pre style="font-size: 8pt; line-height: 140%; margin: 0; ">namespace KRandom {</pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="cm"> * @return A random number in the range [0, RAND_MAX). The RNG is seeded</span></pre></td>
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<td bgcolor="#ffffff" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "><span class="cm"> * @return A random number in the range [0, RAND_MAX). The RNG is seeded</span></pre></td>
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<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">This is wrong. Quoting the man page of rand (3):
"The rand() function returns a pseudo-random integer in the range [0, RAND_MAX]."
Note the closing ']'.</pre>
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<pre style="margin-left: 1em; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">I just copied the existing comment. :)</pre>
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<p style="margin-top: 0;">On August 12th, 2010, 7:17 p.m., <b>Ingo Klöcker</b> wrote:</p>
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<a href="/r/4992/diff/3/?file=33701#file33701line55" style="color: black; font-weight: bold; text-decoration: underline;">trunk/KDE/kdelibs/kdecore/util/krandom.cpp</a>
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(Diff revision 3)
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<td colspan="2"><pre style="font-size: 8pt; line-height: 140%; margin: 0; ">int KRandom::random( int min, int max )</pre></td>
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<td bgcolor="#c5ffc4" width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="k">return</span><span class="p">(</span> <span class="n">random</span><span class="p">()</span> <span class="o">%</span> <span class="p">(</span><span class="n">max</span><span class="o">-</span><span class="n">min</span><span class="o">+</span><span class="mi">1</span><span class="p">)</span> <span class="o">+</span> <span class="n">min</span> <span class="p">);</span></pre></td>
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<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">This will probably crash if you call it with min = MIN_INT and max = MAX_INT because then max-min+1 = 0 (due to an integer overflow). In fact, even smaller ranges will most likely be problematic as soon as max-min+1 > MAX_INT.
Apart from the integer overflow problem this method will not return uniformly distributed random numbers. See for example http://www.cplusplus.com/reference/clibrary/cstdlib/rand/.
If you want uniformly distributed random numbers in a certain integer range then use
http://www.boost.org/doc/libs/1_43_0/doc/html/boost_random/tutorial.html#boost_random.tutorial.generating_integers_in_a_range
instead of trying to re-invent a wheel that is much more complicated than you think.
As far as I'm concerned I'm against adding such a flawed method to kdelibs.</pre>
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<pre style="margin-left: 1em; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">And this is exactly why it makes so much sense to put it in kdecode. There are thousands of ways to get this wrong. I only showed two so far. ;)
And btw: I do not think this is simple. That is why I want your feedback.
I will look at the boost approach and have another go at it.</pre>
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<p>- Sebastian</p>
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<p>On August 12th, 2010, 1:40 p.m., Sebastian Trueg wrote:</p>
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<div>Review request for kdelibs.</div>
<div>By Sebastian Trueg.</div>
<p style="color: grey;"><i>Updated 2010-08-12 13:40:52</i></p>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
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<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">The KRandom namespace is quite useful. However, applications need to be full of code snippets that calculate a random number in a range. IMHO it makes perfect sense to do this once in the library. Thus, I am proposing this patch to introduce two methods providing random numbers from a range.
Feel free to improve the implementation. :)</pre>
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<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
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<li>trunk/KDE/kdelibs/kdecore/util/krandom.h <span style="color: grey">(1162164)</span></li>
<li>trunk/KDE/kdelibs/kdecore/util/krandom.cpp <span style="color: grey">(1162164)</span></li>
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<p><a href="http://reviewboard.kde.org/r/4992/diff/" style="margin-left: 3em;">View Diff</a></p>
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