mpn_sec_add_1_itch

[Torbjörn Granlund]

  > We seem to have forgotten to document that that operand overlap is
  > permitted.  Perhas you could fix that too?  (mpn_mul_1 has it, copying
  > to addmul_1 and submul_1 would probably be sufficient.)
  
  No overlap was intended there (I forgot the length 4 argument in the
  example). But I've done that documentation change too, while at it.
  
I suppose argument overlap there is somewhat unusual, and that that is
the reason why it was not documented.

  I even have an apparently working mod (2^{255} - 19) function now, see
  https://git.lysator.liu.se/nettle/nettle/blob/curve25519/ecc-25519.c

The mod function therein does not necessarily generate principal
remainders, I presume?

Torbjörn
Please encrypt, key id 0xC8601622