+ /*
+ * Endianness-swap. The Curve25519 algorithm definition
+ * assumes you were doing your computation in arrays of 32
+ * little-endian bytes, and now specifies that you take your
+ * final one of those and convert it into a bignum in
+ * _network_ byte order, i.e. big-endian.
+ *
+ * In particular, the spec says, you convert the _whole_ 32
+ * bytes into a bignum. That is, on the rare occasions that
+ * p->x has come out with the most significant 8 bits zero, we
+ * have to imagine that being represented by a 32-byte string
+ * with the last byte being zero, so that has to be converted
+ * into an SSH-2 bignum with the _low_ byte zero, i.e. a
+ * multiple of 256.
+ */