#5320 beam.cc: avoid calculating an invalid reference

[David Kastrup]

beam.cc: avoid calculating an invalid reference

In calc_beam_segments, an invalid reference to a neighboring segment
was calculated (and not used) at the extreme ends of the beam. This
caused segfaults on Fedora. Since the reference is used at most twice
anyway and in the same expression, it seems easier to just use the
expression directly (the invalid cases are then skipped due to
short-circuit evaluation).

http://codereview.appspot.com/343160043

[Simon Albrecht]

Reported here: https://lists.gnu.org/archive/html/bug-lilypond/2018-05/msg00046.html

[Mamoru TASAKA]

Perhaps I don't have right to review patch on codereview site, however patch looks good to me.

[Anonymous]

Passes make, make check and a full make doc

[Anonymous]

Patch on countdown for May 16th

[Anonymous]

Patch counted down - please push

[David Kastrup]

Pushed to staging as
commit d63756608d265d7a99444af1123b7be8a06f3cc2
Author: David Kastrup dak@gnu.org
Date: Wed May 9 13:48:35 2018 +0200

Issue 5320: beam.cc: avoid calculating an invalid reference

In calc_beam_segments, an invalid reference to a neighboring segment
was calculated (and not used) at the extreme ends of the beam.  This
caused segfaults on Fedora.  Since the reference is used at most twice
anyway and in the same expression, it seems easier to just use the
expression directly (the invalid cases are then skipped due to
short-circuit evaluation).