[Patch, libgfortran] PR 25561 Part 1.1/2 Minor improvements to part 1

[Janne Blomqvist]

Hello,

the attached patch does some minor improvements on top of part 1 of the
patch ( http://gcc.gnu.org/ml/gcc-patches/2008-05/msg00769.html ) which
was committed earlier today. As the patch already was quite big, I
didn't want to make reviewers trawl through it again just due to these
minor changes.

It changes the fbuf structure such that the current position in the
structure is an offset from the beginning rather than a pointer. This
makes the buffer manipulation functions a bit simpler.

The main change is that in fbuf_alloc, it avoids keeping already flushed
bytes in case the request doesn't fit into the current buffer. This
avoids the buffer growing without bound if the user is executing many
advance='no' write statements (e.g. in a loop).

It also implements Thomas Koenigs suggestion to use the provided RECL
(if available) as the initial buffer size. Thanks, Thomas!

Regtested on i686-pc-linux-gnu, Ok for trunk?

--
Janne Blomqvist
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