join: improve memory management

* src/join.c (struct seq): Use a (struct line **) for `lines' rather than
one long (struct line *).  This allows individual lines to be swapped out
if necessary.
(reset_line): Get a line ready for new input.
(init_linep): Create a new line and assign it to the the pointer passed in.
(spareline[2]): Hold a spare line for each input file.
(free_spareline): Clean up.
(get_line): Take a (struct line **) instead of a (struct line *).  If the
line to be overwritten is the previous line for the current file then swap
it out for the spare.
(join): Accomodate new structure of SEQs and new parameters to get_line;
Don't free stale lines until the end -- they're re-usable now.
(dup_line): Remove function.
* NEWS: Mention the performance improvement.

1 files changed, 2 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index fe33814e3..30d16b80b 100644
--- a/NEWS
+++ b/NEWS
@@ -31,6 +31,8 @@ GNU coreutils NEWS                                    -*- outline -*-
   HP-UX 11, Tru64, AIX, IRIX 6.5, and Cygwin, "ls -l" now displays the presence
   of an ACL on a file via a '+' sign after the mode, and "cp -p" copies ACLs.
 
+  join has significantly better performance due to better memory management
+
   od now aligns fields across lines when printing multiple -t
   specifiers, and no longer prints fields that resulted entirely from
   padding the input out to the least common multiple width.