Type "make" to check the validity of the f2c source and compile f2c. If (in accordance with what follows) you need to modify the makefile or any of the source files, first issue a "make xsum.out" to check the validity of the f2c source, then make your changes, then type "make f2c". The file usignal.h is for the benefit of strictly ANSI include files on a UNIX system -- the ANSI signal.h does not define SIGHUP or SIGQUIT. You may need to modify usignal.h if you are not running f2c on a UNIX system. Should you get the message "xsum0.out xsum1.out differ", see what lines are different (`diff xsum0.out xsum1.out`) and ask netlib to send you the files in question "from f2c/src". For example, if exec.c and expr.c have incorrect check sums, you would send netlib the message send exec.c expr.c from f2c/src On some systems, the malloc and free in malloc.c let f2c run faster than do the standard malloc and free. Other systems cannot tolerate redefinition of malloc and free. If yours is such a system, you may either modify the makefile appropriately, or simply execute cc -c -DCRAY malloc.c before typing "make". Still other systems have a -lmalloc that provides performance competitive with that from malloc.c; you may wish to compare the two on your system. On some BSD systems, you may need to create a file named "string.h" whose single line is #include you may need to add " -Dstrchr=index" to the "CFLAGS =" assignment in the makefile, and you may need to add " memset.o" to the "OBJECTS =" assignment in the makefile -- see the comments in memset.c . For non-UNIX systems, you may need to change some things in sysdep.c, such as the choice of intermediate file names. On some systems, you may need to modify parts of sysdep.h (which is included by defs.h). In particular, for Sun 4.1 systems and perhaps some others, you need to comment out the typedef of size_t. Alas, some systems #define __STDC__ but do not provide a true standard (ANSI or ISO) C environment, e.g. do not provide stdlib.h . If yours is such a system, then (a) you should complain loudly to your vendor about __STDC__ being erroneously defined, and (b) you should insert #undef __STDC__ at the beginning of sysdep.h . You may need to make other adjustments. For some non-ANSI versions of stdio, you must change the values given to binread and binwrite in sysdep.c from "rb" and "wb" to "r" and "w". You may need to make this change if you run f2c and get an error message of the form Compiler error ... cannot open intermediate file ... On many systems, it is best to combine libF77 and libI77 into a single library, say libf2c, as suggested in "index from f2c". If you do this, then you should adjust the definition of link_msg in sysdep.c appropriately (e.g., replacing "-lF77 -lI77" by "-lf2c"). Some older C compilers object to typedef void (*foo)(); or to typedef void zap; zap (*foo)(); If yours is such a compiler, change the definition of VOID in f2c.h from void to int. Please send bug reports to dmg@research.att.com . The index file ("send index from f2c") will report recent changes in the recent-change log at its end; all changes will be shown in the "fixes" file ("send fixes from f2c"). To keep current source, you will need to request xsum0.out and version.c, in addition to the changed source files.