This changes the buildlink3.mk files to use an include guard for the
recursive include. The use of BUILDLINK_DEPTH, BUILDLINK_DEPENDS,
BUILDLINK_PACKAGES and BUILDLINK_ORDER is handled by a single new
variable BUILDLINK_TREE. Each buildlink3.mk file adds a pair of
enter/exit marker, which can be used to reconstruct the tree and
to determine first level includes. Avoiding := for large variables
(BUILDLINK_ORDER) speeds up parse time as += has linear complexity.
The include guard reduces system time by avoiding reading files over and
over again. For complex packages this reduces both %user and %sys time to
half of the former time.
Half is a class that encapsulates our 16-bit floating-point format.
IlmThread is a thread abstraction library for use with OpenEXR
and other software packages. It currently supports pthreads and
Windows threads.
Imath implements 2D and 3D vectors, 3x3 and 4x4 matrices, quaternions
and other useful 2D and 3D math functions.
Iex is an exception-handling library.
