Extra zero byte converting mpz_t to a string

[Dmitry Antipov]

Hello,

for some strange reason, an attached program outputs an unwanted
trailing zero byte for 6!, 14!, 24!, 29!, 31!, 33!, 40!, 52!, 60!,
65!, 66!, 71!, 79!, 81! and 96!-100! (full output is also attached).

Found on Fedora 21 x86_64 system with vendor's GMP 6.0.0a package
(gmp-6.0.0-9.fc23.src.rpm); reproduced with unstable development
version from hg. Any thoughts?

Dmitry
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#include <stdio.h>
#include <stdlib.h>
#include <gmp.h>

int
main (int argc, char *argv[])
{
  char *s;
  mpz_t v;
  size_t i, j, len;

  mpz_init (v);

  for (i = 1; i <= 100; i++)
    {
      mpz_fac_ui (v, i);

      len = mpz_sizeinbase (v, 10);
      s = mpz_get_str (malloc (len + 2), 10, v);

      printf ("%lu! = ", i);
      for (j = 0; j < len; j++)
	putchar (s[j]);

      if (s[len - 1] == '\0')
	printf (" [trailing zero byte]\n");
      else
	printf (" [ok]\n");
    }

  return 0;
}
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