INSTALLATION INSTRUCTIONS for the Independent JPEG Group's JPEG software

Copyright (C) 1991-1995, Thomas G. Lane.
This file is part of the Independent JPEG Group's software.
For conditions of distribution and use, see the accompanying README file.


This file explains how to configure and install the IJG software.  We have
tried to make this software extremely portable and flexible, so that it can be
adapted to almost any environment.  The downside of this decision is that the
installation process is complicated.  We have provided shortcuts to simplify
the task on common systems.  But in any case, you will need at least a little
familiarity with C programming and program build procedures for your system.

If you are only using this software as part of a larger program, the larger
program's installation procedure may take care of configuring the IJG code.
For example, Ghostscript's installation script will configure the IJG code.
You don't need to read this file if you just want to compile Ghostscript.

If you are on a Unix machine, you may not need to read this file at all.
Try doing
	./configure
	make
	make test
If that doesn't complain, do
	make install
(better do "make -n install" first to see if the makefile will put the files
where you want them).  Read further if you run into snags or want to customize
the code for your system.


TABLE OF CONTENTS
-----------------

Before you start
Configuring the software:
	using the automatic "configure" script
	using one of the supplied jconfig and makefile files
	by hand
Building the software
Testing the software
Installing the software
Optional stuff
Optimization
Hints for specific systems


BEFORE YOU START
================

Before installing the software you must unpack the distributed source code.
Since you are reading this file, you have probably already succeeded in this
task.  However, there is a potential for error if you needed to convert the
files to the local standard text file format (for example, if you are on
MS-DOS you may have converted LF end-of-line to CR/LF).  You must apply
such conversion to all the files EXCEPT those whose names begin with "test".
The test files contain binary data; if you change them in any way then the
self-test will give bad results.

Please check the last section of this file to see if there are hints for the
specific machine or compiler you are using.


CONFIGURING THE SOFTWARE
========================

To configure the IJG code for your system, you need to create two files:
  * jconfig.h: contains values for system-dependent #define symbols.
  * Makefile: controls the compilation process.
(On a non-Unix machine, you may create "project files" or some other
substitute for a Makefile.  jconfig.h is needed in any environment.)

We provide three different ways to generate these files:
  * On a Unix system, you can just run the "configure" script.
  * We provide sample jconfig files and makefiles for popular machines;
    if your machine matches one of the samples, just copy the right sample
    files to jconfig.h and Makefile.
  * If all else fails, read the instructions below and make your own files.


Configuring the software using the automatic "configure" script
---------------------------------------------------------------

If you are on a Unix machine, you can just type
	./configure
and let the configure script construct appropriate configuration files.
If you're using "csh" on an old version of System V, you might need to type
	sh configure
instead to prevent csh from trying to execute configure itself.
Expect configure to run for a few minutes, particularly on slower machines;
it works by compiling a series of test programs.

Configure was created with GNU Autoconf and it follows the usual conventions
for GNU configure scripts.  It makes a few assumptions that you may want to
override.  You can do this by providing optional switches to configure:

* Configure will use gcc (GNU C compiler) if it's available, otherwise cc.
To force a particular compiler to be selected, use the CC option, for example
	./configure CC='cc'
The same method can be used to include any unusual compiler switches.
For example, on HP-UX you probably want to say
	./configure CC='cc -Aa'
to get HP's compiler to run in ANSI mode.

* The default CFLAGS setting is "-O".  You can override this by saying,
for example, ./configure CFLAGS='-O2'.

* Configure will set up the makefile so that "make install" will install files
into /usr/local/bin, /usr/local/man, etc.  You can specify an installation
prefix other than "/usr/local" by giving configure the option "--prefix=PATH".

* If you don't have a lot of swap space, you may need to enable the IJG
software's internal virtual memory mechanism.  To do this, give the option
"--enable-maxmem=N" where N is the default maxmemory limit in megabytes.
This is discussed in more detail under "Selecting a memory manager", below.
You probably don't need to worry about this on reasonably-sized Unix machines,
unless you plan to process very large images.

Configure has some other features that are useful if you are cross-compiling
or working in a network of multiple machine types; but if you need those
features, you probably already know how to use them.


Configuring the software using one of the supplied jconfig and makefile files
-----------------------------------------------------------------------------

If you have one of these systems, you can just use the provided configuration
files:

Makefile	jconfig file	System and/or compiler

makefile.manx	jconfig.manx	Amiga, Manx Aztec C
makefile.sas	jconfig.sas	Amiga, SAS C
mak*jpeg.st	jconfig.st	Atari ST/STE/TT, Pure C or Turbo C
makefile.bcc	jconfig.bcc	MS-DOS or OS/2, Borland C
makefile.dj	jconfig.dj	MS-DOS, DJGPP (Delorie's port of GNU C)
makefile.mc6	jconfig.mc6	MS-DOS, Microsoft C version 6.x and up
makefile.wat	jconfig.wat	MS-DOS, OS/2, or Windows NT, Watcom C
makefile.mms	jconfig.vms	Digital VMS, with MMS software
makefile.vms	jconfig.vms	Digital VMS, without MMS software

Copy the proper jconfig file to jconfig.h and the makefile to Makefile
(or whatever your system uses as the standard makefile name).  For the
Atari, we provide four project files; see the Atari hints below.


Configuring the software by hand
--------------------------------

First, generate a jconfig.h file.  If you are moderately familiar with C,
the comments in jconfig.doc should be enough information to do this; just
copy jconfig.doc to jconfig.h and edit it appropriately.  Otherwise, you may
prefer to use the ckconfig.c program.  You will need to compile and execute
ckconfig.c by hand --- we hope you know at least enough to do that.
ckconfig.c may not compile the first try (in fact, the whole idea is for it
to fail if anything is going to).  If you get compile errors, fix them by
editing ckconfig.c according to the directions given in ckconfig.c.  Once
you get it to run, it will write a suitable jconfig.h file, and will also
print out some advice about which makefile to use.

You may also want to look at the canned jconfig files, if there is one for a
system similar to yours.

Second, select a makefile and copy it to Makefile (or whatever your system
uses as the standard makefile name).  The most generic makefiles we provide
are
	makefile.ansi:	if your C compiler supports function prototypes
	makefile.unix:	if not.
(You have function prototypes if ckconfig.c put "#define HAVE_PROTOTYPES"
in jconfig.h.)  You may want to start from one of the other makefiles if
there is one for a system similar to yours.

Look over the selected Makefile and adjust options as needed.  In particular
you may want to change the CC and CFLAGS definitions.  For instance, if you
are using GCC, set CC=gcc.  If you had to use any compiler switches to get
ckconfig.c to work, make sure the same switches are in CFLAGS.

If you are on a system that doesn't use makefiles, you'll need to set up
project files (or whatever you do use) to compile all the source files and
link them into executable files cjpeg, djpeg, jpegtran, rdjpgcom, and wrjpgcom.
See the file lists in any of the makefiles to find out which files go into
each program.  Note that the provided makefiles all make a "library" file
libjpeg first, but you don't have to do that if you don't want to; the file
lists identify which source files are actually needed for compression,
decompression, or both.  As a last resort, you can make a batch script that
just compiles everything and links it all together; makefile.vms is an example
of this (it's for VMS systems that have no make-like utility).

Here are comments about some specific configuration decisions you'll
need to make:

Command line style
------------------

These programs can use a Unix-like command line style which supports
redirection and piping, like this:
	cjpeg inputfile >outputfile
	cjpeg <inputfile >outputfile
	source program | cjpeg >outputfile
The simpler "two file" command line style is just
	cjpeg inputfile outputfile
You may prefer the two-file style, particularly if you don't have pipes.

You MUST use two-file style on any system that doesn't cope well with binary
data fed through stdin/stdout; this is true for some MS-DOS compilers, for
example.  If you're not on a Unix system, it's safest to assume you need
two-file style.  (But if your compiler provides either the Posix-standard
fdopen() library routine or a Microsoft-compatible setmode() routine, you
can safely use the Unix command line style, by defining USE_FDOPEN or
USE_SETMODE respectively.)

To use the two-file style, make jconfig.h say "#define TWO_FILE_COMMANDLINE".

Selecting a memory manager
--------------------------

The IJG code is capable of working on images that are too big to fit in main
memory; data is swapped out to temporary files as necessary.  However, the
code to do this is rather system-dependent.  We provide four different
memory managers:

* jmemansi.c	This version uses the ANSI-standard library routine tmpfile(),
		which not all non-ANSI systems have.  On some systems
		tmpfile() may put the temporary file in a non-optimal
		location; if you don't like what it does, use jmemname.c.

* jmemname.c	This version creates named temporary files.  For anything
		except a Unix machine, you'll need to configure the
		select_file_name() routine appropriately; see the comments
		near the head of jmemname.c.  If you use this version, define
		NEED_SIGNAL_CATCHER in jconfig.h to make sure the temp files
		are removed if the program is aborted.

* jmemnobs.c	(That stands for No Backing Store :-).)  This will compile on
		almost any system, but it assumes you have enough main memory
		or virtual memory to hold the biggest images you work with.

* jmemdos.c	This should be used with most 16-bit MS-DOS compilers.
		See the system-specific notes about MS-DOS for more info.
		IMPORTANT: if you use this, define USE_MSDOS_MEMMGR in
		jconfig.h, and include the assembly file jmemdosa.asm in the
		programs.  The supplied makefiles and jconfig files for
		MS-DOS compilers already do both.

To use a particular memory manager, change the SYSDEPMEM variable in your
makefile to equal the corresponding object file name (for example, jmemansi.o
or jmemansi.obj for jmemansi.c).

If you have plenty of (real or virtual) main memory, just use jmemnobs.c.
"Plenty" means about ten bytes for every pixel in the largest images
you plan to process, so a lot of systems don't meet this criterion.
If yours doesn't, try jmemansi.c first.  If that doesn't compile, you'll have
to use jmemname.c; be sure to adjust select_file_name() for local conditions.
You may also need to change unlink() to remove() in close_backing_store().

Except with jmemnobs.c, you need to adjust the DEFAULT_MAX_MEM setting to a
reasonable value for your system (either by adding a #define for
DEFAULT_MAX_MEM to jconfig.h, or by adding a -D switch to the Makefile).
This value limits the amount of data space the program will attempt to
allocate.  Code and static data space isn't counted, so the actual memory
needs for cjpeg or djpeg are typically 100 to 150Kb more than the max-memory
setting.  Larger max-memory settings reduce the amount of I/O needed to
process a large image, but too large a value can result in "insufficient
memory" failures.  On most Unix machines (and other systems with virtual
memory), just set DEFAULT_MAX_MEM to several million and forget it.  At the
other end of the spectrum, for MS-DOS machines you probably can't go much
above 300K to 400K.  (On MS-DOS the value refers to conventional memory only.
Extended/expanded memory is handled separately by jmemdos.c.)


BUILDING THE SOFTWARE
=====================

Now you should be able to compile the software.  Just say "make" (or
whatever's necessary to start the compilation).  Have a cup of coffee.

Here are some things that could go wrong:

If your compiler complains about undefined structures, you should be able to
shut it up by putting "#define INCOMPLETE_TYPES_BROKEN" in jconfig.h.

If you have trouble with missing system include files or inclusion of the
wrong ones, read jinclude.h.  This shouldn't happen if you used configure
or ckconfig.c to set up jconfig.h.

There are a fair number of routines that do not use all of their parameters;
some compilers will issue warnings about this, which you can ignore.  There
are also a few configuration checks that may give "unreachable code" warnings.
Any other warning deserves investigation.

If you don't have a getenv() library routine, define NO_GETENV.

Also see the system-specific hints, below.


TESTING THE SOFTWARE
====================

As a quick test of functionality we've included a small sample image in
several forms:
	testorig.jpg	Starting point for the djpeg tests.
	testimg.ppm	The output of djpeg testorig.jpg
	testimg.gif	The output of djpeg -gif testorig.jpg
	testimg.jpg	The output of cjpeg testimg.ppm
	testprog.jpg	Progressive-mode equivalent of testorig.jpg.
	testimgp.jpg	The output of cjpeg -progressive -optimize testimg.ppm
(The first- and second-generation .jpg files aren't identical since JPEG is
lossy.)  If you can generate duplicates of the testimg* files then you
probably have working programs.

With most of the makefiles, "make test" will perform the necessary
comparisons.

If you're using a makefile that doesn't provide the test option, run djpeg
and cjpeg by hand and compare the output files to testimg* with whatever
binary file comparison tool you have.  The files should be bit-for-bit
identical.

If the programs complain "MAX_ALLOC_CHUNK is wrong, please fix", then you
need to reduce MAX_ALLOC_CHUNK to a value that fits in type size_t.
Try adding "#define MAX_ALLOC_CHUNK 65520L" to jconfig.h.  A less likely
configuration error is "ALIGN_TYPE is wrong, please fix": defining ALIGN_TYPE
as long should take care of that one.

If the cjpeg test run fails with "Missing Huffman code table entry", it's a
good bet that you needed to define RIGHT_SHIFT_IS_UNSIGNED.  Go back to the
configuration step and run ckconfig.c.  (This is a good plan for any other
test failure, too.)

If you are using Unix (one-file) command line style on a non-Unix system,
it's a good idea to check that binary I/O through stdin/stdout actually
works.  You should get the same results from "djpeg <testorig.jpg >out.ppm"
as from "djpeg -outfile out.ppm testorig.jpg".  Note that the makefiles all
use the latter style and therefore do not exercise stdin/stdout!  If this
check fails, try recompiling with USE_SETMODE or USE_FDOPEN defined.
If it still doesn't work, better use two-file style.

If you chose a memory manager other than jmemnobs.c, you should test that
temporary-file usage works.  Try "djpeg -gif -max 0 testorig.jpg" and make
sure its output matches testimg.gif.  If you have any really large images
handy, try compressing them with -optimize and/or decompressing with -gif to
make sure your DEFAULT_MAX_MEM setting is not too large.

NOTE: this is far from an exhaustive test of the JPEG software; some modules,
such as 1-pass color quantization, are not exercised at all.  It's just a
quick test to give you some confidence that you haven't missed something
major.


INSTALLING THE SOFTWARE
=======================

Once you're done with the above steps, you can install the software by
copying the executable files (cjpeg, djpeg, jpegtran, rdjpgcom, and wrjpgcom)
to wherever you normally install programs.  On Unix systems, you'll also want
to put the man pages (cjpeg.1, djpeg.1, jpegtran.1, rdjpgcom.1, wrjpgcom.1)
in the man-page directory.  The canned makefiles don't support this step
since there's such a wide variety of installation procedures on different
systems.

If you generated a Makefile with the "configure" script, you can just say
	make install
to install the programs and their man pages into the standard places.
(You'll probably need to be root to do this.)  We recommend first saying
	make -n install
to see where configure thought the files should go.  You may need to edit
the Makefile, particularly if your system's conventions for man page
filenames don't match what configure expects.

If you want to install the library file libjpeg.a and the include files j*.h
(for use in compiling other programs besides the IJG ones), then say
	make install-lib


OPTIONAL STUFF
==============

Progress monitor:

If you like, you can #define PROGRESS_REPORT (in jconfig.h) to enable display
of percent-done progress reports.  The routine provided in cdjpeg.c merely
prints percentages to stderr, but you can customize it to do something
fancier.

Utah RLE file format support:

We distribute the software with support for RLE image files (Utah Raster
Toolkit format) disabled, because the RLE support won't compile without the
Utah library.  If you have URT version 3.1 or later, you can enable RLE
support as follows:
	1.  #define RLE_SUPPORTED in jconfig.h.
	2.  Add a -I option to CFLAGS in the Makefile for the directory
	    containing the URT .h files (typically the "include"
	    subdirectory of the URT distribution).
	3.  Add -L... -lrle to LDLIBS in the Makefile, where ... specifies
	    the directory containing the URT "librle.a" file (typically the
	    "lib" subdirectory of the URT distribution).

Support for 12-bit-deep pixel data:

The JPEG standard allows either 8-bit or 12-bit data precision.  (For color,
this means 8 or 12 bits per channel, of course.)  If you need to work with
deeper than 8-bit data, you can compile the IJG code for 12-bit operation.
To do so:
  1. In jmorecfg.h, define BITS_IN_JSAMPLE as 12 rather than 8.
  2. In jconfig.h, undefine BMP_SUPPORTED, RLE_SUPPORTED, and TARGA_SUPPORTED,
     because the code for those formats doesn't handle 12-bit data and won't
     even compile.  (The PPM code does work, as explained below.  The GIF
     code works too; it scales 8-bit GIF data to and from 12-bit depth
     automatically.)
  3. Compile.  Don't expect "make test" to pass, since the supplied test
     files are for 8-bit data.

Currently, 12-bit support does not work on 16-bit-int machines.

Note that a 12-bit version will not read 8-bit JPEG files, nor vice versa;
so you'll want to keep around a regular 8-bit compilation as well.
(Run-time selection of data depth, to allow a single copy that does both,
is possible but would probably slow things down considerably; it's very low
on our to-do list.)

The PPM reader (rdppm.c) can read 12-bit data from either text-format or
binary-format PPM and PGM files.  Binary-format PPM/PGM files which have a
maxval greater than 255 are assumed to use 2 bytes per sample, LSB first
(little-endian order).  As of early 1995, 2-byte binary format is not
officially supported by the PBMPLUS library, but it is expected that the
next release of PBMPLUS will support it.  Note that the PPM reader will
read files of any maxval regardless of the BITS_IN_JSAMPLE setting; incoming
data is automatically rescaled to either maxval=255 or maxval=4095 as
appropriate for the cjpeg bit depth.

The PPM writer (wrppm.c) will normally write 2-byte binary PPM or PGM
format, maxval 4095, when compiled with BITS_IN_JSAMPLE=12.  Since this
format is not yet widely supported, you can disable it by compiling wrppm.c
with PPM_NORAWWORD defined; then the data is scaled down to 8 bits to make a
standard 1-byte/sample PPM or PGM file.  (Yes, this means still another copy
of djpeg to keep around.  But hopefully you won't need it for very long.
Poskanzer's supposed to get that new PBMPLUS release out Real Soon Now.)

Of course, if you are working with 12-bit data, you probably have it stored
in some other, nonstandard format.  In that case you'll probably want to
write your own I/O modules to read and write your format.

Note that a 12-bit version of cjpeg always runs in "-optimize" mode, in
order to generate valid Huffman tables.  This is necessary because our
default Huffman tables only cover 8-bit data.

Removing code:

If you need to make a smaller version of the JPEG software, some optional
functions can be removed at compile time.  See the xxx_SUPPORTED #defines in
jconfig.h and jmorecfg.h.  If at all possible, we recommend that you leave in
decoder support for all valid JPEG files, to ensure that you can read anyone's
output.  Taking out support for image file formats that you don't use is the
most painless way to make the programs smaller.  Another possibility is to
remove some of the DCT methods: in particular, the "IFAST" method may not be
enough faster than the others to be worth keeping on your machine.  (If you
do remove ISLOW or IFAST, be sure to redefine JDCT_DEFAULT or JDCT_FASTEST
to a supported method, by adding a #define in jconfig.h.)


OPTIMIZATION
============

Unless you own a Cray, you'll probably be interested in making the JPEG
software go as fast as possible.  This section covers some machine-dependent
optimizations you may want to try.  We suggest that before trying any of
this, you first get the basic installation to pass the self-test step.
Repeat the self-test after any optimization to make sure that you haven't
broken anything.

The integer DCT routines perform a lot of multiplications.  These
multiplications must yield 32-bit results, but none of their input values
are more than 16 bits wide.  On many machines, notably the 680x0 and 80x86
CPUs, a 16x16=>32 bit multiply instruction is faster than a full 32x32=>32
bit multiply.  Unfortunately there is no portable way to specify such a
multiplication in C, but some compilers can generate one when you use the
right combination of casts.  See the MULTIPLYxxx macro definitions in
jdct.h.  If your compiler makes "int" be 32 bits and "short" be 16 bits,
defining SHORTxSHORT_32 is fairly likely to work.  When experimenting with
alternate definitions, be sure to test not only whether the code still works
(use the self-test), but also whether it is actually faster --- on some
compilers, alternate definitions may compute the right answer, yet be slower
than the default.  Timing cjpeg on a large PGM (grayscale) input file is the
best way to check this, as the DCT will be the largest fraction of the runtime
in that mode.  (Note: some of the distributed compiler-specific jconfig files
already contain #define switches to select appropriate MULTIPLYxxx
definitions.)

If your machine has sufficiently fast floating point hardware, you may find
that the float DCT method is faster than the integer DCT methods, even
after tweaking the integer multiply macros.  In that case you may want to
make the float DCT be the default method.  (The only objection to this is
that float DCT results may vary slightly across machines.)  To do that, add
"#define JDCT_DEFAULT JDCT_FLOAT" to jconfig.h.  Even if you don't change
the default, you should redefine JDCT_FASTEST, which is the method selected
by djpeg's -fast switch.  Don't forget to update the documentation files
(usage.doc and/or cjpeg.1, djpeg.1) to agree with what you've done.

If access to "short" arrays is slow on your machine, it may be a win to
define type JCOEF as int rather than short.  This will cost a good deal of
memory though, particularly in some multi-pass modes, so don't do it unless
you have memory to burn and short is REALLY slow.

If your compiler can compile function calls in-line, make sure the INLINE
macro in jmorecfg.h is defined as the keyword that marks a function
inline-able.  Some compilers have a switch that tells the compiler to inline
any function it thinks is profitable (e.g., -finline-functions for gcc).
Enabling such a switch is likely to make the compiled code bigger but faster.

In general, it's worth trying the maximum optimization level of your compiler,
and experimenting with any optional optimizations such as loop unrolling.
(Unfortunately, far too many compilers have optimizer bugs ... be prepared to
back off if the code fails self-test.)  If you do any experimentation along
these lines, please report the optimal settings to jpeg-info@uunet.uu.net so
we can mention them in future releases.  Be sure to specify your machine and
compiler version.


HINTS FOR SPECIFIC SYSTEMS
==========================

We welcome reports on changes needed for systems not mentioned here.  Submit
'em to jpeg-info@uunet.uu.net.  Also, if configure or ckconfig.c is wrong
about how to configure the JPEG software for your system, please let us know.


Acorn RISC OS:

(Thanks to Simon Middleton for these hints on compiling with Desktop C.)
After renaming the files according to Acorn conventions, take a copy of
makefile.ansi, change all occurrences of 'libjpeg.a' to 'libjpeg.o' and
change these definitions as indicated:

CFLAGS= -throwback -IC: -Wn
LDLIBS=C:o.Stubs
SYSDEPMEM=jmemansi.o
LN=Link
AR=LibFile -c -o

Also add a new line '.c.o:; $(cc) $< $(cflags) -c -o $@'.  Remove the
lines '$(RM) libjpeg.o' and '$(AR2) libjpeg.o' and the 'jconfig.h'
dependency section.

Copy jconfig.doc to jconfig.h.  Edit jconfig.h to define TWO_FILE_COMMANDLINE
and CHAR_IS_UNSIGNED.

Run the makefile using !AMU not !Make.  If you want to use the 'clean' and
'test' makefile entries then you will have to fiddle with the syntax a bit
and rename the test files.


Amiga:

SAS C 6.50 reportedly is too buggy to compile the IJG code properly.
A patch to update to 6.51 is available from SAS or AmiNet FTP sites.

The supplied config files are set up to use jmemname.c as the memory
manager, with temporary files being created on the device named by
"JPEGTMP:".


Atari ST/STE/TT:
 
Copy the project files makcjpeg.st, makdjpeg.st, maktjpeg.st, and makljpeg.st
to cjpeg.prj, djpeg.prj, jpegtran.prj, and libjpeg.prj respectively.  The
project files should work as-is with Pure C.  For Turbo C, change library
filenames "PC..." to "TC..." in each project file.  Note that libjpeg.prj
selects jmemansi.c as the recommended memory manager.  You'll probably want to
adjust the DEFAULT_MAX_MEM setting --- you want it to be a couple hundred K
less than your normal free memory.  Put "#define DEFAULT_MAX_MEM nnnn" into
jconfig.h to do this.

To use the 68881/68882 coprocessor for the floating point DCT, add the
compiler option "-8" to the project files and replace PCFLTLIB.LIB with
PC881LIB.LIB in cjpeg.prj and djpeg.prj.  Or if you don't have a
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.