There are a few flags that can be turned on and off.
In rsa/bn.h there are
RECP_MUL_MOD	- turn on a faster (a*b)%m routine, should always work.
LONGLONG	- depending on mode, it tries to use a unit 2 times
		  larger if possible.  So for SIXTEEN_BIT - it will use
		  THIRTY_TWO_BIT numbers in some places.  Have a look at
		  bn.h for clarification.  For 32bit machines it is
		  often broken.
SIXTY_FOUR_BIT	- 64 bit units - only tested on DEC Alpha.
THIRTY_TWO_BIT	- 32 bit units - most unix boxes.
SIXTEEN_BIT	- 16 bit units - tested but not normally used.

Have a look in times/times for some number for the best options to
use.

================== MACHINES I HAVE TESTED ON =====================

   Compiled under LINUX by Bill P. <wmperry@spry.com>
   LINUX        x86
	Add -DTERMIO to the CFLAGS in the top level makefile

   SunOS 4.1.3	sparc		cc -O
   SunOS 4.1.3	sparc		gcc -O2 (2.5.7)

   HP-UX 9.04	PA-RISC		gcc -O2 (2.5.7)
   HP-UX 9.04	PA-RISC		cc +O4
	Best results, gcc and LONGLONG.  LONGLONG does not work with cc.

   SunOS 5.3	sparc	 	cc -fast (SC3.0)
   SunOS 5.3	sparc	 	gcc -O2 (2.5.7)
   SunOS 5.4	x86	 	gcc -O2 (2.6.3)
	Uncomment the "EX_LIBS= -lsocket -lnsl" line in the top level
	Makefile.
	Best results, cc -fast, or if you don't have the SC3.0 compiler,
	gcc and LONGLONG

   DGUX 5.4R3.10 mc88110 	gcc -O2 (2.5.8)
	Make sure -DDG_GCC_BUG is defined in the CFLAGS in the top
	level Makefile.
	Best results, use gcc, DO NOT USE LONGLONG

   OSF1 V3.0	alpha		cc -O2
	Turn off THIRTY_TWO_BIT and turn on SIXTY_FOUR_BIT in rsa/bn.h
	Best results, set SIXTY_FOUR_BITS, DO NOT USE LONGLONG, it
	does not work.

   IRIX 4.0.5	mips		cc -O2
   IRIX 5.3	mips		cc -O2
	Make sure -DIRIX_CC_BUG is defined in the CFLAGS in the top
	level Makefile.  DO NOT USE LONGLONG.

   AIX 3.2	RIOS		cc -O
	Add -DAIX to the top level Makefile.  This is to set some
	fd_set macros for ssl/server.c and ssl/client.c
	DO NOT USE LONGLONG, it does not work.
