AP_HAL_SITL: GPIO minor fixes

fix style
make constructor explicit
fix implicit cast for unsigned to signed value
correct DigitalSource constructor definition

libraries/AP_HAL_SITL/GPIO.cpp

@@ -16,22 +16,21 @@ int8_t GPIO::analogPinToDigitalPin(uint8_t pin)
     return pin;
 }
 
-
 uint8_t GPIO::read(uint8_t pin)
 {
-    if (!sitlState->_sitl) {
+    if (!_sitlState->_sitl) {
         return 0;
     }
-    uint8_t mask = sitlState->_sitl->pin_mask.get();
-    return mask & (1U<<pin)? 1: 0;
+    uint8_t mask = static_cast<uint8_t>(_sitlState->_sitl->pin_mask.get());
+    return static_cast<uint8_t>((mask & (1U << pin)) ? 1 : 0);
 }
 
 void GPIO::write(uint8_t pin, uint8_t value)
 {
-    if (!sitlState->_sitl) {
+    if (!_sitlState->_sitl) {
         return;
     }
-    uint8_t mask = sitlState->_sitl->pin_mask.get();
+    uint8_t mask = static_cast<uint8_t>(_sitlState->_sitl->pin_mask.get());
     uint8_t new_mask = mask;
     if (value) {
         new_mask |= (1U << pin);
@@ -39,7 +38,7 @@ void GPIO::write(uint8_t pin, uint8_t value)
         new_mask &= ~(1U << pin);
     }
     if (mask != new_mask) {
-        sitlState->_sitl->pin_mask.set_and_notify(new_mask);
+        _sitlState->_sitl->pin_mask.set_and_notify(new_mask);
     }
 }
 
@@ -50,7 +49,12 @@ void GPIO::toggle(uint8_t pin)
 
 /* Alternative interface: */
 AP_HAL::DigitalSource* GPIO::channel(uint16_t n) {
-    return new DigitalSource(0);
+    if (n < 8) {  // (ie. sizeof(pin_mask)*8)
+        return new DigitalSource(static_cast<uint8_t>(n));
+    } else {
+        return nullptr;
+    }
+
 }
 
 /* Interrupt interface: */
@@ -64,8 +68,8 @@ bool GPIO::usb_connected(void)
     return false;
 }
 
-DigitalSource::DigitalSource(uint8_t v) :
-    pin(v)
+DigitalSource::DigitalSource(uint8_t pin) :
+    _pin(pin)
 {}
 
 void DigitalSource::mode(uint8_t output)
@@ -73,16 +77,16 @@ void DigitalSource::mode(uint8_t output)
 
 uint8_t DigitalSource::read()
 {
-    return hal.gpio->read(pin);
+    return hal.gpio->read(_pin);
 }
 
 void DigitalSource::write(uint8_t value)
 {
-    value = value?1:0;
-    return hal.gpio->write(pin, value);
+    value = static_cast<uint8_t>(value ? 1 : 0);
+    return hal.gpio->write(_pin, value);
 }
 
 void DigitalSource::toggle()
 {
-    return hal.gpio->write(pin, !hal.gpio->read(pin));
+    return hal.gpio->write(_pin, !hal.gpio->read(_pin));
 }

libraries/AP_HAL_SITL/GPIO.h

@@ -4,9 +4,7 @@
 
 class HALSITL::GPIO : public AP_HAL::GPIO {
 public:
-    GPIO(SITL_State *_sitlState) {
-        sitlState = _sitlState;
-    }
+    explicit GPIO(SITL_State *sitlState): _sitlState(sitlState) {}
     void init();
     void pinMode(uint8_t pin, uint8_t output);
     int8_t analogPinToDigitalPin(uint8_t pin);
@@ -25,17 +23,17 @@ public:
     bool usb_connected(void);
 
 private:
-    SITL_State *sitlState;
+    SITL_State *_sitlState;
 };
 
 class HALSITL::DigitalSource : public AP_HAL::DigitalSource {
 public:
-    DigitalSource(uint8_t _pin);
+    explicit DigitalSource(uint8_t pin);
     void mode(uint8_t output);
     uint8_t read();
     void write(uint8_t value);
     void toggle();
 
 private:
-    uint8_t pin;
+    uint8_t _pin;
 };