progress to fsio type safety (#2137)

* rename

* packed type safe fsio value

* comment

* rename

Co-authored-by: Matthew Kennedy <makenne@microsoft.com>

firmware/controllers/core/fsio_core.cpp

@@ -442,4 +442,42 @@ LEElement *LEElementPool::parseExpression(const char * line) {
 	}
 }
 
+FsioValue::FsioValue(float f)
+{
+	u.f32 = f;
+	
+	// The low bit represents whether this is a bool or not, clear it for float
+	u.u32 &= 0xFFFFFFFE;
+}
+
+FsioValue::FsioValue(bool b)
+{
+	u.u32 = (b ? 2 : 0);	// second bit is the actual value of the bool
+
+	// Low bit indicates this is a bool
+	u.u32 |= 0x1;
+}
+
+bool FsioValue::isFloat() const {
+	uint32_t typeBit = u.u32 & 0x1;
+
+	return typeBit == 0;
+}
+
+float FsioValue::asFloat() const {
+	return u.f32;
+}
+
+bool FsioValue::isBool() const {
+	uint32_t typeBit = u.u32 & 0x1;
+
+	return typeBit == 1;
+}
+
+bool FsioValue::asBool() const {
+	uint32_t boolBit = u.u32 & 0x2;
+
+	return boolBit != 0;
+}
+
 #endif /* EFI_FSIO */

firmware/controllers/core/fsio_core.h

@@ -64,6 +64,31 @@ typedef enum {
 
 } le_action_e;
 
+// This type borrows the least significant bit of a float and uses it to indicate
+// whether it's actually a boolean hiding inside that float
+class FsioValue
+{
+public:
+	/*implicit*/ FsioValue(float f);
+	/*implicit*/ FsioValue(bool b);
+
+	bool isFloat() const;
+	float asFloat() const;
+
+	bool isBool() const;
+	bool asBool() const;
+
+private:
+	// These must match for this trick to work!
+	static_assert(sizeof(float) == sizeof(uint32_t));
+
+	union
+	{
+		uint32_t u32;
+		float f32;
+	} u;
+};
+
 using FsioResult = expected<float>;
 
 class LEElement {

unit_tests/tests/test_logic_expression.cpp

@@ -342,3 +342,39 @@ TEST(fsio, fuelPump) {
 	// Pump should be on!
 	EXPECT_TRUE(efiReadPin(GPIOA_0));
 }
+
+TEST(fsio, fsioValueFloat) {
+	FsioValue floatVal(3.5f);
+
+	EXPECT_TRUE(floatVal.isFloat());
+	EXPECT_FALSE(floatVal.isBool());
+
+	EXPECT_FLOAT_EQ(floatVal.asFloat(), 3.5f);
+}
+
+TEST(fsio, fsioValueFloatZero) {
+	FsioValue floatVal(0.0f);
+
+	EXPECT_TRUE(floatVal.isFloat());
+	EXPECT_FALSE(floatVal.isBool());
+
+	EXPECT_FLOAT_EQ(floatVal.asFloat(), 0);
+}
+
+TEST(fsio, fsioValueBoolTrue) {
+	FsioValue boolVal(true);
+
+	EXPECT_TRUE(boolVal.isBool());
+	EXPECT_FALSE(boolVal.isFloat());
+
+	EXPECT_TRUE(boolVal.asBool());
+}
+
+TEST(fsio, fsioValueBoolFalse) {
+	FsioValue boolVal(false);
+
+	EXPECT_TRUE(boolVal.isBool());
+	EXPECT_FALSE(boolVal.isFloat());
+
+	EXPECT_FALSE(boolVal.asBool());
+}