> (key[31]&63)|64

You confused me here; this looks like you're clearing the highest bit and then setting the highest bit... in a 7-bit integer. Of course it makes more sense that you're clearing the two highest bits and then setting the second-highest bit of an 8-bit integer, which is indeed the same thing as clearing the highest bit and then setting the second-highest bit.

But why have you written it to fiddle the second-highest bit twice? Why not just write `(key[31]&127)|64`?

(And then of course, why not use the hexadecimal form of your bitfield constants so people can tell what's going on? No need to count bits that way.)