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POBaffling Inline Behaviour from Random Number Generator Wrapper (C++)
 

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  1. POBaffling Inline Behaviour from Random Number Generator Wrapper (C++)
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    <p>I have a simple wrapper for an Mersenne twister random number generator. The purpose is to scale the number returned by the generator (between 0 and 1) to between argument defined limits (begin and end).</p> <p>So my function is </p> <pre><code>inline float xlRandomFloat(float begin, float end) {return (begin+((end-begin)*genrand_real2()));} </code></pre> <p>I don't believe the implementation of genrand_real2() function is important, but if I am wrong it can be found <a href="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/CODES/mt19937ar.c" rel="nofollow noreferrer">here</a></p> <p>The problem is the function does not return the translated result. The scaling (multiplying by (begin-end) seems to work correctly, but the addition of begin does not seem to be returned.</p> <p>So if I call xlRandomFloat(5,10) - I get values between 0 and 5.</p> <p>If I debug with GDB, and use the print function then it shows the correct result. So then I tried separating things into lines to see what happens</p> <pre><code>inline float xlRandomFloat(float begin, float end) { float ret; ret=(((end-begin)*genrand_real2())); ret+=begin; return ret;}; </code></pre> <p>When debugging, it jumped straight from the first line into the genrand_real2() function and skipped out every thing else entirely. That was really confusing so I thought it may have something to do with the inlining. I moved the file from this .hpp file to the .cpp and removed the inline keyword and everything works correctly.</p> <p>But why does this behavior occur, and how can I inline this function? Also, I am not sure if this is relevant, but often when I made changes to the sources, my Make compilation would say there is nothing to be done. Which is unusual since normally I expect make to pick up on changes in the sources and rebuild accordingly.</p> <p>Any ideas.</p> <p>Thanks</p> <p>Zenna</p>
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