This evening I started writing unit tests for my code, and the first one on the list was the (almost) dead-simple "check direction vector" routine, which is overloaded on Blitz tinyvector length. The one-D case has to ensure that the cosine is bounded by one. Simple enough, right?
inline bool checkDirectionVector(
const blitz::TinyVector<double, 1>& omega)
return (abs(omega) <= 1.0);
Well, in addition to testing that it called a value of 1.0 and -0.5 allowed, I tested whether -1.1 was disallowed. I was flabbergasted when I got the message
/---- Unit test tBlitzStuff failed
| in <build/imclib/tests/tBlitzStuff.cpp> on line 32
which corresponded to the code
mu = -1.1;
What the heck? Then I realized the mistake. My compiler (gcc 4.0) was silently downcasting a double to an integer, truncating -1.1 to -1, and then upcasting the result to the double -1.0, which satisfies the condition.
The solution is simple, to just use
std::fabs(omega)instead. But seriously? I never would have expected a failure on that unit test of all places. These things aren't as worthless as one might think.