Here is a list of compile switches, used to customize Radiance code
for specific machines and users:

-DALIGN=(type)	Alignment type, machine-dependent.  Most RISC
		architectures align on 8-word boundaries (double).
		The default alignment type is int.

-DSPEED=(MIPS)	Millions of instructions per second for this
		processor (approximate).  This is used to decide
		certain unimportant timing issues such as how many
		rays to trace before checking input in rvu and
		whether or not to optimize the color table in ximage
		on 8-bit displays.

-DWFLUSH=(rays)	Override for number of rays before flush in rvu.

-DBSD		Operating system has a strong Berkeley flavor, meaning
		that bcopy() and bzero() are present but maybe memcpy()
		and memset() are not.  (See common/standard.h for other
		things this flag affects.)  Also affects certain system
		calls, such as signal handling and resource tracking.

-DSMLMEM	The system has little RAM available, so size hash
		tables and the like accordingly.  Only allows for
		small scene descriptions (32,256 primitives).

-DSMLFLT	This setting tells Radiance to use short floats
		(32 bits) throughout, which saves lots of memory
		but can cause calculation inaccuracies in many
		cases.  Its use has been discontinued for this reason.

-DSHADCACHE=N	The array size to use for caching occluders.
		Setting this to 0 turns off this optimization.
		Values greater than 20 use over 4 Kbytes per
		light source, which can add up to a lot of
		memory in scenes with many sources.

-DAVGREFL=R	Set the average surface reflectance for the purpose
		of indirect irradiance calculations to R, where
		R is a real number in the range (0,1.0).  The
		default value is 0.50 (50%).  This value indirectly
		controls the maximum number of ambient bounces,
		which can never be more than the log of the -ad
		setting times the log of AVGREFL.