AP_Common: Add type-punning alternative

Signed-off-by: Ryan Friedman <ryanfriedman5410+github@gmail.com>

libraries/AP_Common/AP_Common.cpp

@@ -101,3 +101,39 @@ int16_t char_to_hex(char a)
     else
         return a - '0';
 }
+
+int32_t to_int32(const float value)
+{
+    int32_t out;
+    static_assert(sizeof(value) == sizeof(out));
+
+    // Use memcpy because it's the most portable.
+    // It might not be the fastest way on all hardware.
+    // At least it's defined behavior in both c and c++.
+    memcpy(&out, &value, sizeof(out));
+    return out;
+}
+
+float to_float(const uint32_t value)
+{
+    float out;
+    static_assert(sizeof(value) == sizeof(out));
+
+    // Use memcpy because it's the most portable.
+    // It might not be the fastest way on all hardware.
+    // At least it's defined behavior in both c and c++.
+    memcpy(&out, &value, sizeof(out));
+    return out;
+}
+
+double to_double(const uint64_t value)
+{
+    double out;
+    static_assert(sizeof(value) == sizeof(out));
+
+    // Use memcpy because it's the most portable.
+    // It might not be the fastest way on all hardware.
+    // At least it's defined behavior in both c and c++.
+    memcpy(&out, &value, sizeof(out));
+    return out;
+}

libraries/AP_Common/AP_Common.h

@@ -178,3 +178,19 @@ template <typename T> void BIT_CLEAR (T& value, uint8_t bitnumber) noexcept {
      static_assert(std::is_integral<T>::value, "Integral required.");
      ((value) &= ~((T)(1U) << (bitnumber)));
  }
+
+
+/*
+  Convert from float to int32_t without breaking Wstrict-aliasing due to type punning
+*/
+int32_t to_int32(const float value) WARN_IF_UNUSED;
+
+/*
+  Convert from uint32_t to float without breaking Wstrict-aliasing due to type punning
+*/
+float to_float(const uint32_t value) WARN_IF_UNUSED;
+
+/*
+  Convert from uint64_t to double without breaking Wstrict-aliasing due to type punning
+*/
+double to_double(const uint64_t value) WARN_IF_UNUSED;