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coprocessor, you may prefer to remove the float DCT code by undefining
DCT_FLOAT_SUPPORTED in jmorecfg.h (since without a coprocessor, the float
code will be too slow to be useful).  In that case, you can delete
PCFLTLIB.LIB from the project files.

Note that you must make libjpeg.lib before making cjpeg.ttp, djpeg.ttp,
or jpegtran.ttp.  You'll have to perform the self-test by hand.

We haven't bothered to include project files for rdjpgcom and wrjpgcom.
Those source files should just be compiled by themselves; they don't
depend on the JPEG library.

There is a bug in some older versions of the Turbo C library which causes the
space used by temporary files created with "tmpfile()" not to be freed after
an abnormal program exit.  If you check your disk afterwards, you will find
cluster chains that are allocated but not used by a file.  This should not
happen in cjpeg/djpeg/jpegtran, since we enable a signal catcher to explicitly
close temp files before exiting.  But if you use the JPEG library with your
own code, be sure to supply a signal catcher, or else use a different
system-dependent memory manager.


Cray:

Should you be so fortunate as to be running JPEG on a Cray YMP, there is a
compiler bug in old versions of Cray's Standard C (prior to 3.1).  If you
still have an old compiler, you'll need to insert a line reading
"#pragma novector" just before the loop	
    for (i = 1; i <= (int) htbl->bits[l]; i++)
      huffsize[p++] = (char) l;
in fix_huff_tbl (in V5beta1, line 204 of jchuff.c and line 176 of jdhuff.c).
[This bug may or may not still occur with the current IJG code, but it's
probably a dead issue anyway...]


HP-UX:

If you have HP-UX 7.05 or later with the "software development" C compiler,
you should run the compiler in ANSI mode.  If using the configure script,
say
	./configure CC='cc -Aa'
(or -Ae if you prefer).  If configuring by hand, use makefile.ansi and add
"-Aa" to the CFLAGS line in the makefile.

If you have a pre-7.05 system, or if you are using the non-ANSI C compiler
delivered with a minimum HP-UX system, then you must use makefile.unix
(and do NOT add -Aa); or just run configure without the CC option.

On HP 9000 series 800 machines, the HP C compiler is buggy in revisions prior
to A.08.07.  If you get complaints about "not a typedef name", you'll have to
use makefile.unix, or run configure without the CC option.


Macintosh, MPW:

We don't directly support MPW in the current release, but Larry Rosenstein
ported an earlier version of the IJG code without very much trouble.  There's
useful notes and conversion scripts in his kit for porting PBMPLUS to MPW.
You can obtain the kit by FTP to ftp.apple.com, files /pub/lsr/pbmplus-port*.


Macintosh, Metrowerks CodeWarrior:

Metrowerks release DR2 has problems with the IJG code; don't use it.  Release
DR3.5 or later should be OK.

The command-line-style interface can be used by defining USE_CCOMMAND and
TWO_FILE_COMMANDLINE (see next entry for more details).

On 680x0 Macs, Metrowerks defines type "double" as a 10-byte IEEE extended
float.  jmemmgr.c won't like this: it wants sizeof(ALIGN_TYPE) to be a power
of 2.  Add "#define ALIGN_TYPE long" to jconfig.h to eliminate the complaint.


Macintosh, Think C:

The supplied user-interface files (cjpeg.c and djpeg.c) are set up to provide
a Unix-style command line interface.  You can use this interface on the Mac
by means of Think's ccommand() library routine.  However, a much better
Mac-style user interface has been prepared by Jim Brunner.  You can obtain
the additional source code needed for that user interface by FTP to
sumex-aim.stanford.edu, file /info-mac/dev/src/jpeg-convert-c.hqx.  Jim's
documentation also includes more detailed build instructions for Think C.
(Jim is working on updating this code to work with v5 of the IJG library,
but it wasn't ready as of v5 release time.  Should be out before too long.)

If you want to build the minimal command line version, proceed as follows.
You'll have to prepare project files for the programs; we don't include any
in the distribution since they are not text files.  Use the file lists in
any of the supplied makefiles as a guide.  Also add the ANSI and Unix C
libraries in a separate segment.  You may need to divide the JPEG files into
more than one segment; we recommend dividing compression and decompression
modules.  Define USE_CCOMMAND in jconfig.h so that the ccommand() routine is
called.  You must also define TWO_FILE_COMMANDLINE because stdin/stdout
don't handle binary data correctly.

On 680x0 Macs, Think C defines type "double" as a 12-byte IEEE extended float.
jmemmgr.c won't like this: it wants sizeof(ALIGN_TYPE) to be a power of 2.
Add "#define ALIGN_TYPE long" to jconfig.h to eliminate the complaint.


MIPS R3000:

MIPS's cc version 1.31 has a rather nasty optimization bug.  Don't use -O
if you have that compiler version.  (Use "cc -V" to check the version.)
Note that the R3000 chip is found in workstations from DEC and others.


MS-DOS, generic comments for 16-bit compilers:

The IJG code is designed to be compiled in 80x86 "small" or "medium" memory
models (i.e., data pointers are 16 bits unless explicitly declared "far";
code pointers can be either size).  You may be able to use small model to
compile cjpeg or djpeg by itself, but you will probably have to use medium
model for any larger application.  This won't make much difference in
performance.  You *will* take a noticeable performance hit if you use a
large-data memory model, and you should avoid "huge" model if at all
possible.  Be sure that NEED_FAR_POINTERS is defined in jconfig.h if you use
a small-data memory model; be sure it is NOT defined if you use a large-data
model.  (The supplied makefiles and jconfig files for Borland and Microsoft C
compile in medium model and define NEED_FAR_POINTERS.)

The DOS-specific memory manager, jmemdos.c, should be used if possible.
It needs some assembly-code routines which are in jmemdosa.asm; make sure
your makefile assembles that file and includes it in the library.  If you
don't have a suitable assembler, you can get pre-assembled object files for
jmemdosa by FTP from ftp.uu.net: graphics/jpeg/jdosaobj.zip.  (DOS-oriented
distributions of the IJG source code often include these object files.)

When using jmemdos.c, jconfig.h must define USE_MSDOS_MEMMGR and must set
MAX_ALLOC_CHUNK to less than 64K (65520L is a typical value).  If your
C library's far-heap malloc() can't allocate blocks that large, reduce
MAX_ALLOC_CHUNK to whatever it can handle.

If you can't use jmemdos.c for some reason --- for example, because you
don't have an assembler to assemble jmemdosa.asm --- you'll have to fall
back to jmemansi.c or jmemname.c.  You'll probably still need to set
MAX_ALLOC_CHUNK in jconfig.h, because most DOS C libraries won't malloc()
more than 64K at a time.  IMPORTANT: if you use jmemansi.c or jmemname.c,
you will have to compile in a large-data memory model in order to get the
right stdio library.  Too bad.

wrjpgcom needs to be compiled in large model, because it malloc()s a 64KB
work area to hold the comment text.  If your C library's malloc can't
handle that, reduce MAX_COM_LENGTH as necessary in wrjpgcom.c.

Most MS-DOS compilers treat stdin/stdout as text files, so you must use
two-file command line style.  But if your compiler has either fdopen() or
setmode(), you can use one-file style if you like.  To do this, define
USE_SETMODE or USE_FDOPEN so that stdin/stdout will be set to binary mode.
(USE_SETMODE seems to work with more DOS compilers than USE_FDOPEN.)  You
should test that I/O through stdin/stdout produces the same results as I/O
to explicitly named files... the "make test" procedures in the supplied
makefiles do NOT use stdin/stdout.


MS-DOS, generic comments for 32-bit compilers:

None of the above comments about memory models apply if you are using a
32-bit flat-memory-space environment, such as DJGPP or Watcom C.  (And you
should use one if you have it, as performance will be much better than
8086-compatible code!)  For flat-memory-space compilers, do NOT define
NEED_FAR_POINTERS, and do NOT use jmemdos.c.  Use jmemnobs.c if the
environment supplies adequate virtual memory, otherwise use jmemansi.c or
jmemname.c.

You'll still need to be careful about binary I/O through stdin/stdout.
See the last paragraph of the previous section.


MS-DOS, Borland C:

Be sure to convert all the source files to DOS text format (CR/LF newlines).
Although Borland C will often work OK with unmodified Unix (LF newlines)
source files, sometimes it will give bogus compile errors.
"Illegal character '#'" is the most common such error.  (This is true with
Borland C 3.1, but perhaps is fixed in newer releases.)

If you want one-file command line style, just undefine TWO_FILE_COMMANDLINE.
jconfig.bcc already includes #define USE_SETMODE to make this work.
(fdopen does not work correctly.)


MS-DOS, DJGPP:

Use a recent version of DJGPP (1.11 or better).  If you prefer two-file
command line style, change the supplied jconfig.dj to define
TWO_FILE_COMMANDLINE.  makefile.dj is set up to generate only COFF files
(cjpeg, djpeg, etc) when you say make.  After testing, say "make exe" to
make executables with stub.exe, or "make standalone" if you want executables
that include go32.  You will probably need to tweak the makefile's pointer to
go32.exe to do "make standalone".


MS-DOS, Microsoft C:

If you want one-file command line style, just undefine TWO_FILE_COMMANDLINE.
jconfig.mc6 already includes #define USE_SETMODE to make this work.
(fdopen does not work correctly.)

Old versions of MS C fail with an "out of macro expansion space" error
because they can't cope with the macro TRACEMS8 (defined in jerror.h).
If this happens to you, the easiest solution is to change TRACEMS8 to
expand to nothing.  You'll lose the ability to dump out JPEG coefficient
tables with djpeg -debug -debug, but at least you can compile.

Original MS C 6.0 is very buggy; it compiles incorrect code unless you turn
off optimization entirely (remove -O from CFLAGS).  6.00A is better, but it
still generates bad code if you enable loop optimizations (-Ol or -Ox).

MS C 8.0 reportedly fails to compile jquant1.c if optimization is turned off
(yes, off).


Microsoft Windows (all versions):

Some Windows system include files define typedef boolean as "unsigned char".
The IJG code also defines typedef boolean, but we make it "int" by default.
This doesn't affect the IJG programs because we don't import those Windows
include files.  But if you use the JPEG library in your own program, and some
of your program's files import one definition of boolean while some import the
other, you can get all sorts of mysterious problems.  A good preventive step
is to change jmorecfg.h to define boolean as unsigned char.  We recommend
making that part of jmorecfg.h read like this:
	#ifndef __RPCNDR_H__	/* don't conflict if rpcndr.h already read */
	typedef unsigned char boolean;
	#endif

Many people want to convert the IJG library into a DLL.  This is reasonably
straightforward, but watch out for the following:
  1. Don't try to compile as a DLL in small or medium memory model; use
large model, or even better, 32-bit flat model.  Many places in the IJG code
assume the address of a local variable is an ordinary (not FAR) pointer;
that isn't true in a medium-model DLL.
  2. Microsoft C cannot pass file pointers between applications and DLLs.
(See Microsoft Knowledge Base, PSS ID Number Q50336.)  So jdatasrc.c and
jdatadst.c don't work if you open a file in your application and then pass
the pointer to the DLL.  One workaround is to make jdatasrc.c/jdatadst.c
part of your main application rather than part of the DLL.

The unmodified IJG library presents a very C-specific application interface,
so the resulting DLL is only usable from C or C++ applications.  There has
been some talk of writing wrapper code that would present a simpler interface
usable from other languages, such as Visual Basic.  This is on our to-do list
but hasn't been very high priority --- any volunteers out there?


Microsoft Windows, Borland C:

Borland C++ 4.5 fails with an internal compiler error when trying to compile
jdmerge.c.  If enough people complain, perhaps Borland will fix it.
In the meantime, you can work around the problem by undefining
UPSAMPLE_MERGING_SUPPORTED in jmorecfg.h, at the price of losing most of the
speedup from the "-nosmooth" decompression option.  Alternatively, I'm told
that replacing three or more uses of h2v1_merged_upsample()'s variable
"range_limit" with direct references to "cinfo->sample_range_limit" makes
the problem go away, though the routine is then a little slower than it
should be.  Pretty bizarre, especially since the very similar routine
h2v2_merged_upsample doesn't trigger the bug.


SGI:

Set "AR2= ar -ts" rather than "AR2= ranlib" in the Makefile.  If you are
using configure, you should say
	./configure RANLIB='ar -ts'

On the MIPS R4000 architecture (Indy, etc.), the compiler option "-mips2"
reportedly speeds up the float DCT method substantially, enough to make it
faster than the default int method (but still slower than the fast int
method).  If you use -mips2, you may want to alter the default DCT method to
be float.  To do this, put "#define JDCT_DEFAULT JDCT_FLOAT" in jconfig.h.


VMS:

On an Alpha/VMS system with MMS, be sure to use the "/Marco=Alpha=1"
qualifier with MMS when building the JPEG package.

VAX/VMS v5.5-1 may have problems with the test step of the build procedure
reporting differences when it compares the original and test images.  If the
error points to the last block of the files, it is most likely bogus and may
be safely ignored.  It seems to be because the files are Stream_LF and
Backup/Compare has difficulty with the (presumably) null padded files.
This problem was not observed on VAX/VMS v6.1 or AXP/VMS v6.1.