** ERROR **: file strtod-test.c: line 49 (main): assertion failed: (d == g_ascii_strtod (g_ascii_dtostr (buffer, sizeof (buffer), d), NULL))
aborting...

adding these lines before that:

  printf ("(builtin) d is %.15e\n", d);
  g_printf ("(trio)    d is %.15e\n", d);

yields:

  (builtin) d is 5.190168296483627e-309
  (trio)    d is 5.190168296483618e-309