Re: proposed gnulib-related additions to Autoconf

[Paul Eggert]

Ralf Wildenhues <address@hidden> writes:

> First, there is still a bug in both your version and mine, AFAICS: if
> you pass a MIN-VARIABLE for an unsigned entity, and that variable is not
> yet defined, it computes the wrong result.

I assume this can be fixed by replacing:

                  [$ac_min1 < $ac_min && ($1) $ac_min1 == $ac_min1]

with:

                  [$ac_min1 < $ac_min && ($1) $ac_min1 == $ac_min1
                   && ($1) $ac_min1 < 0]

so that we don't execute the ac_min=$ac_min1 assignment by mistake.

> Eric mentioned the desire for a macro to compute all of stdint.
> So I decided it was worthwhile to have one that does not expand to
> megabytes of redundant code, even if it was very slow.  Thus the
> version below allows shell variables as arguments.

I don't quite follow the motivation here, sorry.  (This is the most
important point, ...)

> Would you rather prefer a BITS-VARIABLE to a VALUE-BITS-VARIABLE, by
> the way?

I'm not sure why one would need a bits-variable; can't you just use
sizeof (type) * CHAR_BIT?

> Currently the VALUE-BITS-VARIABLE is not tested for being defined
> already.  Should that be included for safety?

I wouldn't bother, for now.

> I tried to accomodate for all that was brought up in the previous
> discussion.  The testsuite found one more subtle bug: in this code
>   while :; do
>    AC_COMPILE_IFELSE([program], [if-true], [break])
>   done
>
> the break will inhibit the cleanup code that removes conftest.c

I should have remembered that.  We can fix that without using an extra
status variable by using this sort of idea:

  # Double the number of bits until this fails.
  while
    $3[]1=`expr $$3 '*' 2`
    ac_max="((((($1) 1 << ($$3 - 1 - $2)) - 1) << 1) + 1)"
    ac_max1="((((($1) 1 << ($$3[]1 - 1 - $2)) - 1) << 1) + 1)"
    AC_COMPILE_IFELSE(
      [AC_LANG_BOOL_COMPILE_TRY([AC_INCLUDES_DEFAULT([$4])],
         [$ac_max < $ac_max1 && ($1) $ac_max1 == $ac_max1])],
      [$3=$$3[]1])
    test $3 = $$3[]1
  do :
  done