mini-gmp: mpz_init_set_str fails on leading zeroes

Torbjörn Granlund tg at
Thu Jul 28 12:33:25 UTC 2016

nisse at (Niels Möller) writes:

  Austyn Krutsinger <akrutsinger at> writes:
  > We can fix this in the mpn_set_str_other function by changing the
  > comparison in line 1321. If we accept that w can be > or = to 0, then there
  > is no issue if the number has leading zeros. So line 1321 in
  > mpn_set_str_other becomes:
  > 1321   for (rn = (w >= 0); j < sn;)
  Checking what the fine manual says on mpn_set_str:
       The converted value is {RP,RN} where RN is the return value.  If
       the most significant input byte STR[0] is non-zero, then RP[RN-1]
       will be non-zero, else RP[RN-1] and some number of subsequent limbs
       may be zero.
  So I think it's fine to always initialize rn to 1. And then mpz_set_str
  will have to either strip leading zeros in the input to mpn_set_str, or
  normalize the result afterwards.
  Since this is mini-gmp, another option which is fine if it turns
  out to be simpler, is to add an if (!n) return 0; to the start of
  mpn_mul_1, and an appropriate comment somewhere. Then mpn_set_str will
  produce always normalized output, with no changes.
Let's not diverge foo in GMP and foo in mini-gmp.  Or at least let's not
rely on divergence.  Because if we do, that will some day that will come
back and bite us.

So please make mini-gmp use any re-implemented gmp interface function
only so that instead using the gmp function (intentionally or
accidentally) would work.

Please encrypt, key id 0xC8601622

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