- int version; // increment when data values change
- int pad; // keep doubles 64-bit aligned for some
- // hardware platforms, such as the Sun
- // SPARC, which don't like misaligned
- // data
-
- // Positions
- double longitude; // geodetic (radians)
- double latitude; // geodetic (radians)
- float altitude; // above sea level (meters)
- float agl; // above ground level (meters)
- float phi; // roll (radians)
- float theta; // pitch (radians)
- float psi; // yaw or true heading (radians)
+// Note: align fields properly and manually to avoid incompatibilities
+// between 32bit and 64bit CPUs. Make sure that each field is already
+// placed on an offset which is a multiple of the size of its data
+// type, i.e. uint32/float need to have on offset of 4, doubles need
+// an offset of 8. This guarantees that compilers will _not_ add
+// CPU-specific padding bytes. Whenever in doubt about padding rules,
+// check "data structure alignment" in Wikipedia/Google :).
+
+ uint32_t version; // increment when data values change
+ uint32_t padding1; // 4 padding bytes, so the next (64bit) var is aligned to 8
+
+ // Positions (note: offset for these doubles is already aligned to 8 - to avoid architecture specific alignments)
+ double longitude; // geodetic (radians)
+ double latitude; // geodetic (radians)
+
+ float altitude; // above sea level (meters)
+ float agl; // above ground level (meters)
+ float phi; // roll (radians)
+ float theta; // pitch (radians)
+ float psi; // yaw or true heading (radians)