pbio/drivebase: Fix curve direction for zero radius.

It is more intuitive to reverse the angle only for
strictly negative radii. This way, a curve with zero
radius behaves the same as the turn() method.

Author: laurensvalk

CHANGELOG.md

@@ -5,7 +5,15 @@
 ## [Unreleased]
 
 ### Changed
-- Renamed new `DCMotor.dc_settings()` method to `DCMotor.settings()`.
+- Renamed new `DCMotor.dc_settings()` method
+  to `DCMotor.settings()` ([support#536]).
+
+### Fixed
+- Fixed direction for `DriveBase.turn()` and `Drivebase.curve()` for some
+  arguments ([support#535]).
+
+[support#535]: https://github.com/pybricks/support/issues/535
+[support#536]: https://github.com/pybricks/support/issues/536
 
 ## [3.1.0c1] - 2021-11-19
 

lib/pbio/src/drivebase.c

@@ -341,7 +341,7 @@ pbio_error_t pbio_drivebase_drive_curve(pbio_drivebase_t *db, int32_t radius, in
     } else {
         // In the normal case, angle_or_distance is interpreted as the angle,
         // signed by the radius. Arc length is computed accordingly.
-        arc_angle = radius > 0 ? angle_or_distance : -angle_or_distance;
+        arc_angle = radius < 0 ? -angle_or_distance : angle_or_distance;
         arc_length = (10 * abs(angle_or_distance) * radius) / 573;
     }