32-bit [non-]support

[DavidBuchanan314]

This code was written with 64-bit platforms in mind. If sizeof(size_t) == 4, bad things might happen (wrt. integer overflows related to the length of large buffers).

I should either make sure it works safely on 32-bit platforms (I suspect not!), or prevent it from building on 32-bit platforms.

[DavidBuchanan314]

I suppose a lot of old raspberry pis are 32-bit still (or at least, 32-bit userland), and that is something I'd like to support.

[DavidBuchanan314]

32-bit builds are now prevented by 4f257db, but I'd still like to fix this properly

[DavidBuchanan314]

One issue here is confusion between size_t (which is (usually) 32-bit on 32-bit platforms) and CBOR lengths, which are 64-bit.

I should probably make a cbor_length_to_size_t() helper, which is a nop on 64-bit systems, and errors on 32-bit systems if the size is too big

[DavidBuchanan314]

SIZE_MAX from limits.h will tell us the max size that size_t can hold. ((uint64_t)-1) tells us the max size that uint64_t can hold.

[DavidBuchanan314]

7bb3b1b fixed a bug on 32-bit platforms, and aside from that it works, but may still be unsafe.