Remove typedef's and bool enum

[DictumMortuum]

Your types are unnecessary - just use unsigned char and int as the standard library would.

On the same topic, your enum bool is unnecessary because in C non-zero indicates the true state. You confirm that yourself because get() assumes that the value 1 is true. Everyone assumes this and so the type is redundant. Moreover it is also wrong because if I change your enum to

typedef enum{true=0, false} bool;
your function fails, even though it is logically a reasonable thing to do.

If you want to use a bool like that your should return one of its values explicitly:

return ((a >> pos) & 1) ? true : false;
but there is really no point in this. Just return an int as the standard library would.

[DictumMortuum]

This applies to external sort, too.