[BUGFIX] fix qgsRound for negative numbers. Fixes #20861

lbartoletti · nyalldawson · commit 3f0171b8bfa3 · 2019-02-01T20:07:31.000+11:00
(cherry picked from commit cfdc8c2)
diff --git a/src/core/qgis.h b/src/core/qgis.h
@@ -316,8 +316,9 @@ inline bool qgsDoubleNearSig( double a, double b, int significantDigits = 10 )
  */
 inline double qgsRound( double number, double places )
 {
+  double m = ( number < 0.0 ) ? -1.0 : 1.0;
   double scaleFactor = std::pow( 10.0, places );
-  return std::trunc( number * scaleFactor + 0.5 ) / scaleFactor;
+  return ( std::round( number * m * scaleFactor ) / scaleFactor ) * m;
 }
 
 
diff --git a/tests/src/core/testqgis.cpp b/tests/src/core/testqgis.cpp
@@ -339,6 +339,8 @@ void TestQgis::testQgsAsConst()
 
 void TestQgis::testQgsRound()
 {
+  QGSCOMPARENEAR( qgsRound( 1234.567, 2 ), 1234.57, 0.01 );
+  QGSCOMPARENEAR( qgsRound( -1234.567, 2 ), -1234.57, 0.01 );
   QGSCOMPARENEAR( qgsRound( 98765432198, 8 ), 98765432198, 1.0 );
   QGSCOMPARENEAR( qgsRound( 98765432198, 9 ), 98765432198, 1.0 );
   QGSCOMPARENEAR( qgsRound( 98765432198, 10 ), 98765432198, 1.0 );
@@ -354,9 +356,9 @@ void TestQgis::testQgsRound()
   QGSCOMPARENEAR( qgsRound( 9.8765432198765, 5 ), 9.87654, 0.000001 );
   QGSCOMPARENEAR( qgsRound( 9.8765432198765, 6 ), 9.876543, 0.0000001 );
   QGSCOMPARENEAR( qgsRound( 9.8765432198765, 7 ), 9.8765432, 0.00000001 );
-  QGSCOMPARENEAR( qgsRound( -9.8765432198765, 7 ), -9.876543, 0.000001 );
+  QGSCOMPARENEAR( qgsRound( -9.8765432198765, 7 ), -9.8765432, 0.0000001 );
   QGSCOMPARENEAR( qgsRound( 9876543.2198765, 5 ), 9876543.219880, 0.000001 );
-  QGSCOMPARENEAR( qgsRound( -9876543.2198765, 5 ), -9876543.219870, 0.000001 );
+  QGSCOMPARENEAR( qgsRound( -9876543.2198765, 5 ), -9876543.219880, 0.000001 );
   QGSCOMPARENEAR( qgsRound( 9.87654321987654321, 13 ), 9.87654321987654, 0.0000000000001 );
   QGSCOMPARENEAR( qgsRound( 9.87654321987654321, 14 ), 9.876543219876543, 0.00000000000001 );
   QGSCOMPARENEAR( qgsRound( 9998.87654321987654321, 14 ), 9998.876543219876543, 0.00000000000001 );

Original file line number	Diff line number	Diff line change
`@@ -316,8 +316,9 @@ inline bool qgsDoubleNearSig( double a, double b, int significantDigits = 10 )`
`316`	`316`	`*/`
`317`	`317`	`inline double qgsRound( double number, double places )`
`318`	`318`	`{`
	`319`	`+ double m = ( number < 0.0 ) ? -1.0 : 1.0;`
`319`	`320`	`double scaleFactor = std::pow( 10.0, places );`
`320`		`- return std::trunc( number * scaleFactor + 0.5 ) / scaleFactor;`
	`321`	`+ return ( std::round( number * m * scaleFactor ) / scaleFactor ) * m;`
`321`	`322`	`}`
`322`	`323`
`323`	`324`