Throw exception if RNG is used with invalid bounds.

common/rng_sfmt.cpp

@@ -1,6 +1,7 @@
 #include "rng_sfmt.h"
 #include <QDateTime>
 #include <algorithm>
+#include <stdexcept>
 
 // This is from gcc sources, namely from fixincludes/inclhack.def
 // On C++11 systems, <cstdint> could be included instead.
@@ -57,12 +58,17 @@ RNG_SFMT::RNG_SFMT(QObject *parent)
  */
 unsigned int RNG_SFMT::getNumber(unsigned int min, unsigned int max)
 {
-	// This all makes no sense if min > max.
-	// So in debug mode Q_ASSERT will print a warning...
-	Q_ASSERT(min <= max);
-	// ... and at runtime min and max will be swapped; this should never happen.
-	if(min > max)
-	  std::swap(min, max);
+	// This all makes no sense if min > max, which should never happen.
+	if(min > max) {
+		throw std::invalid_argument(
+		  QString("Invalid bounds for RNG: min > max! Values were: min = " +
+		  QString::number(min) + ", max = " +
+		  QString::number(max) +
+		  ". This is either a bug or something even more serious happened."
+		  ).toStdString());
+		// at this point, the method exits. No return value is needed, because
+		// basically the exception itself is returned.
+	}
 
 	// First compute the diameter (aka size, length) of the [min, max] interval
 	const unsigned int diameter = max - min + 1;

common/rng_sfmt.h

@@ -7,7 +7,14 @@
 
 /**
  * This class represents the random number generator.
- * It uses the SIMD-oriented Fast Mersenne Twister code v1.4.1 from
+ * Usage instructions:
+ * Create an instance of RNG_SFMT, then call getNumber(min, max).
+ * You should never call this function with min > max, this throws a
+ * std::invalid_argument exception. It is best practice to use getNumber() in a try block
+ * and catch the exception if min, max are entered by the user or computed somehow.
+ *
+ * Technical details:
+ * The RNG uses the SIMD-oriented Fast Mersenne Twister code v1.4.1 from
  * http://www.math.sci.hiroshima-u.ac.jp/~%20m-mat/MT/SFMT/index.html
  * To use this RNG, the class needs a sfmt_t structure for the RNG's internal state.
  * It has to be initialized by sfmt_init_gen_rand() which is done in the constructor.