Add rand and randf functions for generating random numbers

Author: nyalldawson

resources/function_help/rand-en_US

@@ -0,0 +1,16 @@
+<h3>rand() function</h3>
+Returns a random integer within the range specified by the minimum and 
+maximum argument (inclusive).
+<br>
+This function takes two arguments.
+<h4>Syntax</h4>
+<code>rand(min, max)</code><br>
+
+<h4>Arguments</h4>
+<code>min</code> - an integer representing the smallest possible random number desired.<br>
+<code>max</code> - an integer representing the largest possible random number desired.
+<br>
+
+<h4>Example</h4>
+<!-- Show example of function.-->
+<code>rand(1, 10) &rarr; 8</code><br>

resources/function_help/randf-en_US

@@ -0,0 +1,16 @@
+<h3>rand() function</h3>
+Returns a random float within the range specified by the minimum and 
+maximum argument (inclusive).
+<br>
+This function takes two arguments.
+<h4>Syntax</h4>
+<code>randf(min, max)</code><br>
+
+<h4>Arguments</h4>
+<code>min</code> - a float representing the smallest possible random number desired.<br>
+<code>max</code> - a float representing the largest possible random number desired.
+<br>
+
+<h4>Example</h4>
+<!-- Show example of function.-->
+<code>randf(1, 10) &rarr; 4.59258286403147</code><br>

src/app/main.cpp

@@ -294,6 +294,9 @@ int main( int argc, char *argv[] )
   SetUnhandledExceptionFilter( qgisCrashDump );
 #endif
 
+  // initialize random number seed
+  srand( time( NULL ) );
+
   /////////////////////////////////////////////////////////////////
   // Command line options 'behaviour' flag setup
   ////////////////////////////////////////////////////////////////

src/core/qgsexpression.cpp

@@ -410,6 +410,27 @@ static QVariant fcnLog( const QVariantList& values, QgsFeature* , QgsExpression*
     return QVariant();
   return QVariant( log( x ) / log( b ) );
 }
+static QVariant fcnRndF( const QVariantList& values, QgsFeature* , QgsExpression* parent )
+{
+  double min = getDoubleValue( values.at( 0 ), parent );
+  double max = getDoubleValue( values.at( 1 ), parent );
+  if ( max < min )
+    return QVariant();
+
+  // Return a random double in the range [min, max] (inclusive)
+  double f = ( double )rand() / RAND_MAX;
+  return QVariant( min + f * ( max - min ) ) ;
+}
+static QVariant fcnRnd( const QVariantList& values, QgsFeature* , QgsExpression* parent )
+{
+  int min = getIntValue( values.at( 0 ), parent );
+  int max = getIntValue( values.at( 1 ), parent );
+  if ( max < min )
+    return QVariant();
+
+  // Return a random integer in the range [min, max] (inclusive)
+  return QVariant( min + ( rand() % ( int )( max - min + 1 ) ) );
+}
 static QVariant fcnToInt( const QVariantList& values, QgsFeature* , QgsExpression* parent )
 {
   return QVariant( getIntValue( values.at( 0 ), parent ) );
@@ -1207,7 +1228,7 @@ const QStringList &QgsExpression::BuiltinFunctions()
     << "sqrt" << "cos" << "sin" << "tan"
     << "asin" << "acos" << "atan" << "atan2"
     << "exp" << "ln" << "log10" << "log"
-    << "round" << "toint" << "toreal" << "tostring"
+    << "round" << "rand" << "randf" << "toint" << "toreal" << "tostring"
     << "todatetime" << "todate" << "totime" << "tointerval"
     << "coalesce" << "regexp_match" << "$now" << "age" << "year"
     << "month" << "week" << "day" << "hour"
@@ -1246,6 +1267,8 @@ const QList<QgsExpression::Function*> &QgsExpression::Functions()
     << new StaticFunction( "log10", 1, fcnLog10, QObject::tr( "Math" ) )
     << new StaticFunction( "log", 2, fcnLog, QObject::tr( "Math" ) )
     << new StaticFunction( "round", -1, fcnRound, QObject::tr( "Math" ) )
+    << new StaticFunction( "rand", 2, fcnRnd, QObject::tr( "Math" ) )
+    << new StaticFunction( "randf", 2, fcnRndF, QObject::tr( "Math" ) )
     << new StaticFunction( "$pi", 0, fcnPi, QObject::tr( "Math" ) )
     << new StaticFunction( "toint", 1, fcnToInt, QObject::tr( "Conversions" ) )
     << new StaticFunction( "toreal", 1, fcnToReal, QObject::tr( "Conversions" ) )

tests/src/core/testqgsexpression.cpp

@@ -454,6 +454,40 @@ class TestQgsExpression: public QObject
       QCOMPARE( v.toInt(), 200 );
     }
 
+    void eval_rand()
+    {
+      QgsExpression exp1( "rand(1,10)" );
+      QVariant v1 = exp1.evaluate();
+      QCOMPARE( v1.toInt() <= 10, true );
+      QCOMPARE( v1.toInt() >= 1, true );
+
+      QgsExpression exp2( "rand(-5,-5)" );
+      QVariant v2 = exp2.evaluate();
+      QCOMPARE( v2.toInt(), -5 );
+
+      // Invalid expression since max<min
+      QgsExpression exp3( "rand(10,1)" );
+      QVariant v3 = exp3.evaluate();
+      QCOMPARE( v3.type(),  QVariant::Invalid );
+    }
+
+    void eval_randf()
+    {
+      QgsExpression exp1( "randf(1.5,9.5)" );
+      QVariant v1 = exp1.evaluate();
+      QCOMPARE( v1.toDouble() <= 9.5, true );
+      QCOMPARE( v1.toDouble() >= 1.5, true );
+
+      QgsExpression exp2( "randf(-0.0005,-0.0005)" );
+      QVariant v2 = exp2.evaluate();
+      QCOMPARE( v2.toDouble(), -0.0005 );
+
+      // Invalid expression since max<min
+      QgsExpression exp3( "randf(9.3333,1.784)" );
+      QVariant v3 = exp3.evaluate();
+      QCOMPARE( v3.type(),  QVariant::Invalid );
+    }
+
     void referenced_columns()
     {
       QSet<QString> expectedCols;