Careful with casting strings to ints like that, it'll break on architectures that require aligned accesses, i.e. if you try to load a uint32, the address of the memory location must be a multiple of 4. x86 happens to be fine with non-aligned access, but many other architectures aren't.

If you look at the nginx source, that #define is guarded under NGX_HAVE_NONALIGNED and there is a fallback that does straight byte by byte comparison.