Support underscores for mpz/mpq assignments from strings

[Vincent Lefevre]

On 2021-06-14 14:50:43 +0200, Hans Åberg wrote:
> 
> > On 14 Jun 2021, at 10:59, Vincent Lefevre <vincent at vinc17.net> wrote:
> > 
> > On 2021-06-11 18:20:01 +0200, Hans Åberg wrote:
> >> But you can probably cannot change mpz_set_str,
> >> because it is modelled on C behavior.
> > 
> > It isn't. In C, whitespace isn't a separator.
> 
> The GMP manual, sec. 5.2, is not clear on this, as it says that whitespace is discarded, whereas in C/C++ it is only the initial whitespace.

I think that the GMP manual is clear: mpz_set_str ignores whitespace
anywhere in the string (contrary to C's strtod, etc.).

In mpz/set_str.c:

  /* Remove spaces from the string and convert the result from ASCII to a
     byte array.  */
  for (i = 0; i < str_size; i++)
    {
      if (!isspace (c))
        {
          int dig = digit_value[c];
          if (UNLIKELY (dig >= base))
            {
              TMP_FREE;
              return -1;
            }
          *s++ = dig;
        }
      c = (unsigned char) *str++;
    }

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