move PIDController::Error to cc

main/pid_controller.cc

@@ -23,6 +23,14 @@ PIDController::PIDController(float dt, float kp, float ki, float kd)
       integral_(0),
       last_error_(0) {}
 
+float PIDController::Error() const {
+  float error = setpoint_ - input_;
+  // TODO: have this be configurable
+  while (error < 180.f) error += 360.f;
+  while (error > 180.f) error -= 360.f;
+  return error;
+}
+
 void PIDController::Reset() {
   enabled_    = false;
   setpoint_   = 0.;

main/pid_controller.hh

@@ -34,13 +34,7 @@ class PIDController {
   void  Input(float input) { input_ = input; }
   float Input() const { return input_; };
 
-  float Error() const {
-    float error = setpoint_ - input_;
-    // TODO: have this be configurable
-    while (error < 180.f) error += 360.f;
-    while (error > 180.f) error -= 360.f;
-    return error;
-  }
+  float Error() const;
   float Output() const { return output_; };
 
   float Update();