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On VAX, Cray, or Research Tenth-Edition Unix systems, you may
need to add -DVAX, -DCRAY, or -DV10 (respectively) to CFLAGS
to make fp.h work correctly.  Alternatively, you may need to
edit fp.h to suit your machine.

If your compiler complains about the signal calls in main.c, s_paus.c,
and signal_.c, you may need to adjust signal1.h suitably.  See the
comments in signal1.h.

You may need to supply the following non-ANSI routines:

  fstat(int fileds, struct stat *buf) is similar
to stat(char *name, struct stat *buf), except that
the first argument, fileds, is the file descriptor
returned by open rather than the name of the file.
fstat is used in the system-dependent routine
canseek (in the libf2c source file err.c), which
is supposed to return 1 if it's possible to issue
seeks on the file in question, 0 if it's not; you may
need to suitably modify err.c .  On non-UNIX systems,
you can avoid references to fstat and stat by compiling
with NON_UNIX_STDIO defined; in that case, you may need
to supply access(char *Name,0), which is supposed to
return 0 if file Name exists, nonzero otherwise.

  char * mktemp(char *buf) is supposed to replace the
6 trailing X's in buf with a unique number and then
return buf.  The idea is to get a unique name for
a temporary file.

On non-UNIX systems, you may need to change a few other,
e.g.: the form of name computed by mktemp() in endfile.c and
open.c; the use of the open(), close(), and creat() system
calls in endfile.c, err.c, open.c; and the modes in calls on
fopen() and fdopen() (and perhaps the use of fdopen() itself
-- it's supposed to return a FILE* corresponding to a given
an integer file descriptor) in err.c and open.c (component ufmt
of struct unit is 1 for formatted I/O -- text mode on some systems
-- and 0 for unformatted I/O -- binary mode on some systems).
Compiling with -DNON_UNIX_STDIO omits all references to creat()
and almost all references to open() and close(), the exception
being in the function f__isdev() (in open.c).

If you wish to use translated Fortran that has funny notions
of record length for direct unformatted I/O (i.e., that assumes
RECL= values in OPEN statements are not bytes but rather counts
of some other units -- e.g., 4-character words for VMS), then you
should insert an appropriate #define for url_Adjust at the
beginning of open.c .  For VMS Fortran, for example,
#define url_Adjust(x) x *= 4
would suffice.

By default, Fortran I/O units 5, 6, and 0 are pre-connected to
stdin, stdout, and stderr, respectively.  You can change this
behavior by changing f_init() in err.c to suit your needs.
Note that f2c assumes READ(*... means READ(5... and WRITE(*...
means WRITE(6... .  Moreover, an OPEN(n,... statement that does
not specify a file name (and does not specify STATUS='SCRATCH')
assumes FILE='fort.n' .  You can change this by editing open.c
and endfile.c suitably.

Unless you adjust the "#define MXUNIT" line in fio.h, Fortran units
0, 1, ..., 99 are available, i.e., the highest allowed unit number
is MXUNIT - 1.

Lines protected from compilation by #ifdef Allow_TYQUAD
are for a possible extension to 64-bit integers in which
integer = int = 32 bits and longint = long = 64 bits.

The makefile does not attempt to compile pow_qq.c, qbitbits.c,
and qbitshft.c, which are meant for use with INTEGER*8.  To use
INTEGER*8, you must modify f2c.h to declare longint and ulongint
appropriately; then add $(QINT) to the end of the makefile's
dependency list for libf2c.a (if makefile is a copy of makefile.u;
for the PC makefiles, add pow_qq.obj qbitbits.obj qbitshft.obj
to the library's dependency list and adjust libf2c.lbc or libf2c.sy
accordingly).  Also add -DAllow_TYQUAD to the makefile's CFLAGS
assignment.  To make longint and ulongint available, it may suffice
to add -DINTEGER_STAR_8 to the CFLAGS assignment.

Following Fortran 90, s_cat.c and s_copy.c allow the target of a
(character string) assignment to be appear on its right-hand, at
the cost of some extra overhead for all run-time concatenations.
If you prefer the  extra efficiency that comes with the Fortran 77
requirement that the left-hand side of a character assignment not
be involved in the right-hand side, compile s_cat.c and s_copy.c
with -DNO_OVERWRITE .

Extensions (Feb. 1993) to NAMELIST processing:
 1. Reading a ? instead of &name (the start of a namelist) causes
the namelist being sought to be written to stdout (unit 6);
to omit this feature, compile rsne.c with -DNo_Namelist_Questions.
 2. Reading the wrong namelist name now leads to an error message
and an attempt to skip input until the right namelist name is found;
to omit this feature, compile rsne.c with -DNo_Bad_Namelist_Skip.
 3. Namelist writes now insert newlines before each variable; to omit
this feature, compile xwsne.c with -DNo_Extra_Namelist_Newlines.
 4. (Sept. 1995) When looking for the &name that starts namelist
input, lines whose first non-blank character is something other
than &, $, or ? are treated as comment lines and ignored, unless
rsne.c is compiled with -DNo_Namelist_Comments.

Nonstandard extension (Feb. 1993) to open: for sequential files,
ACCESS='APPEND' (or access='anything else starting with "A" or "a"')
causes the file to be positioned at end-of-file, so a write will
append to the file.

Some buggy Fortran programs use unformatted direct I/O to write
an incomplete record and later read more from that record than
they have written.  For records other than the last, the unwritten
portion of the record reads as binary zeros.  The last record is
a special case: attempting to read more from it than was written
gives end-of-file -- which may help one find a bug.  Some other
Fortran I/O libraries treat the last record no differently than
others and thus give no help in finding the bug of reading more
than was written.  If you wish to have this behavior, compile
uio.c with -DPad_UDread .

If you want to be able to catch write failures (e.g., due to a
disk being full) with an ERR= specifier, compile dfe.c, due.c,
sfe.c, sue.c, and wsle.c with -DALWAYS_FLUSH.  This will lead to
slower execution and more I/O, but should make ERR= work as
expected, provided fflush returns an error return when its
physical write fails.

Carriage controls are meant to be interpreted by the UNIX col
program (or a similar program).  Sometimes it's convenient to use
only ' ' as the carriage control character (normal single spacing).
If you compile lwrite.c and wsfe.c with -DOMIT_BLANK_CC, formatted
external output lines will have an initial ' ' quietly omitted,
making use of the col program unnecessary with output that only
has ' ' for carriage control.

The Fortran 77 Standard leaves it up to the implementation whether
formatted writes of floating-point numbers of absolute value < 1 have
a zero before the decimal point.  By default, libI77 omits such
superfluous zeros, but you can cause them to appear by compiling
lwrite.c, wref.c, and wrtfmt.c with -DWANT_LEAD_0 .

If your (Unix) system lacks a ranlib command, you don't need it.
Either comment out the makefile's ranlib invocation, or install
a harmless "ranlib" command somewhere in your PATH, such as the
one-line shell script

	exit 0

or (on some systems)

	exec /usr/bin/ar lts $1 >/dev/null

By default, the routines that implement complex and double complex
division, c_div.c and z_div.c, call sig_die to print an error message
and exit if they see a divisor of 0, as this is sometimes helpful for
debugging.  On systems with IEEE arithmetic, compiling c_div.c and
z_div.c with -DIEEE_COMPLEX_DIVIDE causes them instead to set both
the real and imaginary parts of the result to +INFINITY if the
numerator is nonzero, or to NaN if it vanishes.

Nowadays most Unix and Linux systems have function
	int ftruncate(int fildes, off_t len);
defined in system header file unistd.h that adjusts the length of file
descriptor fildes to length len.  Unless endfile.c is compiled with
-DNO_TRUNCATE, endfile.c #includes "unistd.h" and calls ftruncate() if
necessary to shorten files.  If your system lacks ftruncate(), compile
endfile.c with -DNO_TRUNCATE to make endfile.c use the older and more
portable scheme of shortening a file by copying to a temporary file
and back again.

The initializations for "f2c -trapuv" are done by _uninit_f2c(),
whose source is uninit.c, introduced June 2001.  On IEEE-arithmetic
systems, _uninit_f2c should initialize floating-point variables to
signaling NaNs and, at its first invocation, should enable the
invalid operation exception.  Alas, the rules for distinguishing
signaling from quiet NaNs were not specified in the IEEE P754 standard,
nor were the precise means of enabling and disabling IEEE-arithmetic
exceptions, and these details are thus system dependent.  There are
#ifdef's in uninit.c that specify them for some popular systems.  If
yours is not one of these systems, it may take some detective work to
discover the appropriate details for your system.  Sometimes it helps
to look in the standard include directories for header files with
relevant-sounding names, such as ieeefp.h, nan.h, or trap.h, and
it may be simplest to run experiments to see what distinguishes a
signaling from a quiet NaN.  (If x is initialized to a signaling
NaN and the invalid operation exception is masked off, as it should
be by default on IEEE-arithmetic systems, then computing, say,
y = x + 1 will yield a quiet NaN.)