*******************************************************************************
** Building on Unix Platforms (including Cygwin)
*******************************************************************************
==================
Build Requirements
==================
-- autoconf 2.56 or later
-- automake 1.7 or later
-- libtool 1.4 or later
-- NASM (if building x86 or x86-64 SIMD extensions)
* 0.98, or 2.01 or later is required for a 32-bit build
* NASM 2.00 or later is required for a 64-bit build
* NASM 2.07 or later is required for a 64-bit build on OS X. This can be
obtained from MacPorts (http://www.macports.org/).
The binary RPMs released by the NASM project do not work on older Linux
systems, such as Red Hat Enterprise Linux 4. On such systems, you can
easily build and install NASM from a source RPM by downloading one of the
SRPMs from
http://www.nasm.us/pub/nasm/releasebuilds
and executing the following as root:
ARCH=`uname -m`
rpmbuild --rebuild nasm-{version}.src.rpm
rpm -Uvh /usr/src/redhat/RPMS/$ARCH/nasm-{version}.$ARCH.rpm
NOTE: the NASM build will fail if texinfo is not installed.
-- GCC v4.1 or later recommended for best performance
-- If building the TurboJPEG/OSS Java wrapper, JDK or OpenJDK 1.5 or later is
required. Some systems, such as OS X 10.4, Solaris 10 and later, and Red
Hat Enterprise Linux 5 and later, have this pre-installed. On OS X 10.5 and
later, it will be necessary to install the Java Developer Package, which can
be downloaded from http://connect.apple.com. For systems that do not have a
JDK installed, you can obtain the Oracle Java Development Kit from
http://www.java.com.
==================
Out-of-Tree Builds
==================
Binary objects, libraries, and executables are generated in the same directory
from which configure was executed (the "binary directory"), and this directory
need not necessarily be the same as the libjpeg-turbo source directory. You
can create multiple independent binary directories, in which different versions
of libjpeg-turbo can be built from the same source tree using different
compilers or settings. In the sections below, {build_directory} refers to the
binary directory, whereas {source_directory} refers to the libjpeg-turbo source
directory. For in-tree builds, these directories are the same.
======================
Building libjpeg-turbo
======================
The following procedure will build libjpeg-turbo on Linux, FreeBSD, 32-bit
OS X, Cygwin, and Solaris/x86 systems (on Solaris, this generates a 32-bit
library. See below for 64-bit build instructions.)
cd {source_directory}
autoreconf -fiv
cd {build_directory}
sh {source_directory}/configure [additional configure flags]
make
NOTE: Running autoreconf in the source directory is only necessary if building
libjpeg-turbo from the SVN repository.
This will generate the following files under .libs/
libjpeg.a
Static link library for libjpeg-turbo
libjpeg.so.{version} (Linux, Solaris)
libjpeg.{version}.dylib (OS X)
cygjpeg-{version}.dll (Cygwin)
Shared library for libjpeg-turbo
libjpeg.so (Linux, Solaris)
libjpeg.dylib (OS X)
libjpeg.dll.a (Cygwin)
Development stub for libjpeg-turbo shared library
libturbojpeg.a
Static link library for TurboJPEG/OSS
libturbojpeg.so (Linux, Solaris)
libturbojpeg.dylib (OS X)
Shared library and development stub for TurboJPEG/OSS
cygturbojpeg.dll (Cygwin)
Shared library for TurboJPEG/OSS
libturbojpeg.dll.a (Cygwin)
Development stub for TurboJPEG/OSS shared library
{version} is 62.0.0, 7.0.0, or 8.0.2, depending on whether libjpeg v6b
(default), v7, or v8 emulation is enabled. If using Cygwin, {version} is
62, 7, or 8.
libjpeg v7 or v8 API/ABI Emulation
----------------------------------
Add --with-jpeg7 to the configure command line to build a version of
libjpeg-turbo that is API/ABI-compatible with libjpeg v7. Add --with-jpeg8 to
the configure command to build a version of libjpeg-turbo that is
API/ABI-compatible with libjpeg v8. See README-turbo.txt for more information
on libjpeg v7 and v8 emulation.
Arithmetic Coding Support
-------------------------
Since the patent on arithmetic coding has expired, this functionality has been
included in this release of libjpeg-turbo. libjpeg-turbo's implementation is
based on the implementation in libjpeg v8, but it works when emulating libjpeg
v7 or v6b as well. The default is to enable both arithmetic encoding and
decoding, but those who have philosophical objections to arithmetic coding can
add --without-arith-enc or --without-arith-dec to the configure command line to
disable encoding or decoding (respectively.)
TurboJPEG/OSS Java Wrapper
--------------------------
Add --with-java to the configure command line to incorporate an optional Java
Native Interface wrapper into the TurboJPEG/OSS dynamic library and build the
Java front-end classes to support it. This allows the TurboJPEG/OSS dynamic
library to be used directly from Java applications. See java/README for more
details.
You can set the JAVAC, JAR, and JAVA configure variables to specify
alternate commands for javac, jar, and java (respectively.) You can also
set the JAVACFLAGS configure variable to specify arguments that should be
passed to the Java compiler when building the front-end classes, and JNI_CFLAGS
to specify arguments that should be passed to the C compiler when building the
JNI wrapper. Run 'configure --help' for more details.
========================
Installing libjpeg-turbo
========================
If you intend to install these libraries and the associated header files, then
replace 'make' in the instructions above with
make install prefix={base dir} libdir={library directory}
For example,
make install prefix=/usr/local libdir=/usr/local/lib64
will install the header files in /usr/local/include and the library files in
/usr/local/lib64. If 'prefix' and 'libdir' are not specified, then the default
is to install the header files in /opt/libjpeg-turbo/include and the library
files in /opt/libjpeg-turbo/lib.
NOTE: You can specify a prefix of /usr and a libdir of, for instance,
/usr/lib64 to overwrite the system's version of libjpeg. If you do this,
however, then be sure to BACK UP YOUR SYSTEM'S INSTALLATION OF LIBJPEG before
overwriting it. It is recommended that you instead install libjpeg-turbo into
a non-system directory and manipulate the LD_LIBRARY_PATH or create sym links
to force applications to use libjpeg-turbo instead of libjpeg. See
README-turbo.txt for more information.
=============
Build Recipes
=============
32-bit Library Build on 64-bit Linux
------------------------------------
Add
--host i686-pc-linux-gnu CFLAGS='-O3 -m32' LDFLAGS=-m32
to the configure command line.
64-bit Library Build on 64-bit OS X
-----------------------------------
Add
--host x86_64-apple-darwin NASM=/opt/local/bin/nasm
to the configure command line. NASM 2.07 or later from MacPorts must be
installed.
32-bit Library Build on 64-bit OS X
-----------------------------------
Add
CFLAGS='-O3 -m32' LDFLAGS=-m32
to the configure command line.
64-bit Backward-Compatible Library Build on 64-bit OS X
-------------------------------------------------------
Add
--host x86_64-apple-darwin NASM=/opt/local/bin/nasm \
CFLAGS='-isysroot /Developer/SDKs/MacOSX10.4u.sdk \
-mmacosx-version-min=10.4 -O3' \
LDFLAGS='-isysroot /Developer/SDKs/MacOSX10.4u.sdk \
-mmacosx-version-min=10.4'
to the configure command line. The OS X 10.4 SDK, and NASM 2.07 or later from
MacPorts, must be installed.
32-bit Backward-Compatible Library Build on OS X
------------------------------------------------
Add
CFLAGS='-isysroot /Developer/SDKs/MacOSX10.4u.sdk \
-mmacosx-version-min=10.4 -O3 -m32' \
LDFLAGS='-isysroot /Developer/SDKs/MacOSX10.4u.sdk \
-mmacosx-version-min=10.4 -m32'
to the configure command line. The OS X 10.4 SDK must be installed.
64-bit Library Build on 64-bit Solaris
--------------------------------------
Add
--host x86_64-pc-solaris CFLAGS='-O3 -m64' LDFLAGS=-m64
to the configure command line.
32-bit Library Build on 64-bit FreeBSD
--------------------------------------
Add
--host i386-unknown-freebsd CC='gcc -B /usr/lib32' CFLAGS='-O3 -m32' \
LDFLAGS='-B/usr/lib32'
to the configure command line. NASM 2.07 or later from FreeBSD ports must be
installed.
Sun Studio
----------
Add
CC=cc
to the configure command line. libjpeg-turbo will automatically be built with
the maximum optimization level (-xO5) unless you override CFLAGS.
To build a 64-bit version of libjpeg-turbo using Sun Studio, add
--host x86_64-pc-solaris CC=cc CFLAGS='-xO5 -m64' LDFLAGS=-m64
to the configure command line.
MinGW Build on Cygwin
---------------------
Use CMake (see recipes below)
===========
ARM Support
===========
This release of libjpeg-turbo can use ARM NEON SIMD instructions to accelerate
JPEG compression/decompression by approximately 2-4x on ARMv7 and later
platforms. If libjpeg-turbo is configured on an ARM Linux platform, then the
build system will automatically include the NEON SIMD routines, if they are
supported.
Building libjpeg-turbo for iOS
------------------------------
iOS platforms, such as the iPhone and iPad, also use ARM processors, some of
which support NEON instructions. Additional steps are required to build
libjpeg-turbo for these platforms. The steps below assume iOS SDK v4.3. If
you are using a different SDK version, then you will need to modify the
examples accordingly.
Additional build requirements:
gas-preprocessor.pl (https://github.com/yuvi/gas-preprocessor) should be
installed in your PATH.
Set the following shell variables for simplicity:
IOS_PLATFORMDIR="/Developer/Platforms/iPhoneOS.platform"
IOS_SYSROOT="$IOS_PLATFORMDIR/Developer/SDKs/iPhoneOS4.3.sdk"
IOS_GCC="$IOS_PLATFORMDIR/Developer/usr/bin/arm-apple-darwin10-llvm-gcc-4.2"
ARM v6 only (up to and including iPhone 3G):
IOS_CFLAGS="-march=armv6 -mcpu=arm1176jzf-s -mfpu=vfp"
ARM v7 only (iPhone 3GS and newer, iPad):
IOS_CFLAGS="-march=armv7 -mcpu=cortex-a8 -mtune=cortex-a8 -mfpu=neon"
Follow the procedure under "Building libjpeg-turbo" above, adding
--host arm-apple-darwin10 --enable-static --disable-shared \
CC="$IOS_GCC" LD="$IOS_GCC" \
CFLAGS="-mfloat-abi=softfp -isysroot $IOS_SYSROOT -O3 $IOS_CFLAGS" \
LDFLAGS="-mfloat-abi=softfp -isysroot $IOS_SYSROOT $IOS_CFLAGS"
to the configure command line.
Once built, lipo can be used to combine the ARM v6 and v7 variants into a
universal library.
*******************************************************************************
** Building on Windows (Visual C++ or MinGW)
*******************************************************************************
==================
Build Requirements
==================
-- CMake (http://www.cmake.org) v2.6 or later
-- Microsoft Visual C++ 2005 or later
If you don't already have Visual C++, then the easiest way to get it is by
installing the Windows SDK:
http://msdn.microsoft.com/en-us/windows/bb980924.aspx
The Windows SDK includes both 32-bit and 64-bit Visual C++ compilers and
everything necessary to build libjpeg-turbo.
* For 32-bit builds, you can also use Microsoft Visual C++ Express
Edition. Visual C++ Express Edition is a free download.
* If you intend to build libjpeg-turbo from the command line, then add the
appropriate compiler and SDK directories to the INCLUDE, LIB, and PATH
environment variables. This is generally accomplished by executing
vcvars32.bat or vcvars64.bat and SetEnv.cmd. vcvars32.bat and
vcvars64.bat are part of Visual C++ and are located in the same directory
as the compiler. SetEnv.cmd is part of the Windows SDK. You can pass
optional arguments to SetEnv.cmd to specify a 32-bit or 64-bit build
environment.
... OR ...
-- MinGW
GCC v4.1 or later recommended for best performance
-- NASM (http://www.nasm.us/) 0.98 or later (NASM 2.05 or later is required for
a 64-bit build)
-- If building the TurboJPEG/OSS Java wrapper, JDK 1.5 or later is required.
This can be downloaded from http://www.java.com.
==================
Out-of-Tree Builds
==================
Binary objects, libraries, and executables are generated in the same directory
from which cmake was executed (the "binary directory"), and this directory need
not necessarily be the same as the libjpeg-turbo source directory. You can
create multiple independent binary directories, in which different versions of
libjpeg-turbo can be built from the same source tree using different compilers
or settings. In the sections below, {build_directory} refers to the binary
directory, whereas {source_directory} refers to the libjpeg-turbo source
directory. For in-tree builds, these directories are the same.
======================
Building libjpeg-turbo
======================
Visual C++ (Command Line)
-------------------------
cd {build_directory}
cmake -G "NMake Makefiles" -DCMAKE_BUILD_TYPE=Release {source_directory}
nmake
This will build either a 32-bit or a 64-bit version of libjpeg-turbo, depending
on which version of cl.exe is in the PATH.
The following files will be generated under {build_directory}:
jpeg-static.lib
Static link library for libjpeg-turbo
sharedlib/jpeg{version}.dll
DLL for libjpeg-turbo
sharedlib/jpeg.lib
Import library for libjpeg-turbo DLL
turbojpeg-static.lib
Static link library for TurboJPEG/OSS
turbojpeg.dll
DLL for TurboJPEG/OSS
turbojpeg.lib
Import library for TurboJPEG/OSS DLL
{version} is 62, 7, or 8, depending on whether libjpeg v6b (default), v7, or
v8 emulation is enabled.
Visual C++ (IDE)
----------------
Choose the appropriate CMake generator option for your version of Visual Studio
(run "cmake" with no arguments for a list of available generators.) For
instance:
cd {build_directory}
cmake -G "Visual Studio 9 2008" {source_directory}
You can then open ALL_BUILD.vcproj in Visual Studio and build one of the
configurations in that project ("Debug", "Release", etc.) to generate a full
build of libjpeg-turbo.
This will generate the following files under {build_directory}:
{configuration}/jpeg-static.lib
Static link library for libjpeg-turbo
sharedlib/{configuration}/jpeg{version}.dll
DLL for libjpeg-turbo
sharedlib/{configuration}/jpeg.lib
Import library for libjpeg-turbo DLL
{configuration}/turbojpeg-static.lib
Static link library for TurboJPEG/OSS
{configuration}/turbojpeg.dll
DLL for TurboJPEG/OSS
{configuration}/turbojpeg.lib
Import library for TurboJPEG/OSS DLL
{configuration} is Debug, Release, RelWithDebInfo, or MinSizeRel, depending on
the configuration you built in the IDE, and {version} is 62, 7, or 8,
depending on whether libjpeg v6b (default), v7, or v8 emulation is enabled.
MinGW
-----
cd {build_directory}
cmake -G "MSYS Makefiles" {source_directory}
make
This will generate the following files under {build_directory}
libjpeg.a
Static link library for libjpeg-turbo
sharedlib/libjpeg-{version}.dll
DLL for libjpeg-turbo
sharedlib/libjpeg.dll.a
Import library for libjpeg-turbo DLL
libturbojpeg.a
Static link library for TurboJPEG/OSS
libturbojpeg.dll
DLL for TurboJPEG/OSS
libturbojpeg.dll.a
Import library for TurboJPEG/OSS DLL
{version} is 62, 7, or 8, depending on whether libjpeg v6b (default), v7, or
v8 emulation is enabled.
Debug Build
-----------
Add "-DCMAKE_BUILD_TYPE=Debug" to the cmake command line. Or, if building with
NMake, remove "-DCMAKE_BUILD_TYPE=Release" (Debug builds are the default with
NMake.)
libjpeg v7 or v8 API/ABI Emulation
-----------------------------------
Add "-DWITH_JPEG7=1" to the cmake command line to build a version of
libjpeg-turbo that is API/ABI-compatible with libjpeg v7. Add "-DWITH_JPEG8=1"
to the cmake command to build a version of libjpeg-turbo that is
API/ABI-compatible with libjpeg v8. See README-turbo.txt for more information
on libjpeg v7 and v8 emulation.
Arithmetic Coding Support
-------------------------
Since the patent on arithmetic coding has expired, this functionality has been
included in this release of libjpeg-turbo. libjpeg-turbo's implementation is
based on the implementation in libjpeg v8, but it works when emulating libjpeg
v7 or v6b as well. The default is to enable both arithmetic encoding and
decoding, but those who have philosophical objections to arithmetic coding can
add "-DWITH_ARITH_ENC=0" or "-DWITH_ARITH_DEC=0" to the cmake command line to
disable encoding or decoding (respectively.)
TurboJPEG/OSS Java Wrapper
--------------------------
Add "-DWITH_JAVA=1" to the cmake command line to incorporate an optional Java
Native Interface wrapper into the TurboJPEG/OSS dynamic library and build the
Java front-end classes to support it. This allows the TurboJPEG/OSS dynamic
library to be used directly from Java applications. See java/README for more
details.
If you are using CMake 2.8, you can set the Java_JAVAC_EXECUTABLE,
Java_JAVA_EXECUTABLE, and Java_JAR_EXECUTABLE CMake variables to specify
alternate commands or locations for javac, jar, and java (respectively.) If
you are using CMake 2.6, set JAVA_COMPILE, JAVA_RUNTIME, and JAVA_ARCHIVE
instead. You can also set the JAVACFLAGS CMake variable to specify arguments
that should be passed to the Java compiler when building the front-end classes.
========================
Installing libjpeg-turbo
========================
You can use the build system to install libjpeg-turbo into a directory of your
choosing (as opposed to creating an installer.) To do this, add:
-DCMAKE_INSTALL_PREFIX={install_directory}
to the cmake command line.
For example,
cmake -G "NMake Makefiles" -DCMAKE_BUILD_TYPE=Release \
-DCMAKE_INSTALL_PREFIX=c:\libjpeg-turbo {source_directory}
nmake install
will install the header files in c:\libjpeg-turbo\include, the library files
in c:\libjpeg-turbo\lib, the DLL's in c:\libjpeg-turbo\bin, and the
documentation in c:\libjpeg-turbo\doc.
=============
Build Recipes
=============
64-bit MinGW Build on Cygwin
----------------------------
cd {build_directory}
CC=/usr/bin/x86_64-w64-mingw32-gcc \
cmake -G "Unix Makefiles" -DCMAKE_SYSTEM_NAME=Windows \
-DCMAKE_AR=/usr/bin/x86_64-w64-mingw32-ar \
-DCMAKE_RANLIB=/usr/bin/x86_64-w64-mingw32-ranlib {source_directory}
make
This produces a 64-bit build of libjpeg-turbo that does not depend on
cygwin1.dll or other Cygwin DLL's. The mingw64-x86_64-gcc-core and
mingw64-x86_64-gcc-g++ packages (and their dependencies) must be installed.
32-bit MinGW Build on Cygwin
----------------------------
cd {build_directory}
CC=/usr/bin/i686-w64-mingw32-gcc \
cmake -G "Unix Makefiles" -DCMAKE_SYSTEM_NAME=Windows \
-DDCMAKE_AR=/usr/bin/i686-w64-mingw32-ar \
-DCMAKE_RANLIB=/usr/bin/i686-w64-mingw32-ranlib {source_directory}
make
This produces a 32-bit build of libjpeg-turbo that does not depend on
cygwin1.dll or other Cygwin DLL's. The mingw64-i686-gcc-core and
mingw64-i686-gcc-g++ packages (and their dependencies) must be installed.
MinGW-w64 Build on Windows
--------------------------
This produces a 64-bit build of libjpeg-turbo using the "native" MinGW-w64
toolchain (which is faster than the Cygwin version):
cd {build_directory}
CC={mingw-w64_binary_path}/x86_64-w64-mingw32-gcc \
cmake -G "MSYS Makefiles" \
-DCMAKE_AR={mingw-w64_binary_path}/x86_64-w64-mingw32-ar \
-DCMAKE_RANLIB={mingw-w64_binary_path}/x86_64-w64-mingw32-ranlib \
{source_directory}
make
MinGW Build on Linux
--------------------
cd {build_directory}
CC={mingw_binary_path}/i386-mingw32-gcc \
cmake -G "Unix Makefiles" -DCMAKE_SYSTEM_NAME=Windows \
-DCMAKE_AR={mingw_binary_path}/i386-mingw32-ar \
-DCMAKE_RANLIB={mingw_binary_path}/i386-mingw32-ranlib \
{source_directory}
make
*******************************************************************************
** Creating Release Packages
*******************************************************************************
The following commands can be used to create various types of release packages:
Unix
----
make rpm
Create Red Hat-style binary RPM package. Requires RPM v4 or later.
make srpm
This runs 'make dist' to create a pristine source tarball, then creates a
Red Hat-style source RPM package from the tarball. Requires RPM v4 or later.
make deb
Create Debian-style binary package. Requires dpkg.
make dmg
Create Macintosh package/disk image. This requires the PackageMaker
application, which must be installed in /Developer/Applications/Utilities.
make udmg [BUILDDIR32={32-bit build directory}]
On 64-bit OS X systems, this creates a Macintosh package and disk image that
contains universal i386/x86-64 binaries. You should first configure a 32-bit
out-of-tree build of libjpeg-turbo, then configure a 64-bit out-of-tree
build, then run 'make udmg' from the 64-bit build directory. The build
system will look for the 32-bit build under {source_directory}/osxx86 by
default, but you can override this by setting the BUILDDIR32 variable on the
make command line as shown above.
make iosdmg [BUILDDIR32={32-bit build directory}] \
[BUILDDIRARMV6={ARM v6 build directory}] \
[BUILDDIRARMV7={ARM v7 build directory}] \
On OS X systems, this creates a Macintosh package and disk image in which the
libjpeg-turbo static libraries contain ARM architectures necessary to build
iOS applications. If building on an x86-64 system, the binaries will also
contain the i386 architecture, as with 'make udmg' above. You should first
configure ARM v6 and ARM v7 out-of-tree builds of libjpeg-turbo (see
"Building libjpeg-turbo for iOS" above.) If you are building an x86-64
version of libjpeg-turbo, you should configure a 32-bit out-of-tree build as
well. Next, build libjpeg-turbo as you would normally, using an out-of-tree
build. When it is built, run 'make iosdmg' from the build directory. The
build system will look for the ARM v6 build under {source_directory}/iosarmv6
by default, the ARM v7 build under {source_directory}/iosarmv7 by default,
and (if applicable) the 32-bit build under {source_directory}/osxx86 by
default, but you can override this by setting the BUILDDIR32, BUILDDIRARMV6,
and/or BUILDDIRARMV7 variables on the make command line as shown above.
make sunpkg
Build a Solaris package. This requires pkgmk, pkgtrans, and bzip2.
make csunpkg [BUILDDIR32={32-bit build directory}]
On 64-bit Solaris systems, this creates a combined package that contains
both 32-bit and 64-bit libraries. You should first configure a 32-bit
out-of-tree build of libjpeg-turbo, then configure a 64-bit out-of-tree
build, then run 'make csunpkg' from the 64-bit build directory. The build
system will look for the 32-bit build under {source_directory}/solx86 by
default, but you can override this by setting the BUILDDIR32 variable on the
make command line as shown above.
make cygwinpkg
Build a Cygwin binary package.
Windows
-------
If using NMake:
cd {build_directory}
nmake installer
If using MinGW:
cd {build_directory}
make installer
If using the Visual Studio IDE, build the "installer" project.
The installer package (libjpeg-turbo[-gcc][64].exe) will be located under
{build_directory}. If building using the Visual Studio IDE, then the installer
package will be located in a subdirectory with the same name as the
configuration you built (such as {build_directory}\Debug\ or
{build_directory}\Release\).
Building a Windows installer requires the Nullsoft Install System
(http://nsis.sourceforge.net/.) makensis.exe should be in your PATH.
*******************************************************************************
** Regression testing
*******************************************************************************
The most common way to test libjpeg-turbo is by invoking 'make test' on
Unix/Linux platforms or 'ctest' on Windows platforms, once the build has
completed. This runs a series of tests to ensure that mathematical
compatibility has been maintained between libjpeg-turbo and libjpeg v6b. This
also invokes the TurboJPEG unit tests, which ensure that the colorspace
extensions, YUV encoding, decompression scaling, and other features of the
TurboJPEG C and Java APIs are working properly (and, by extension, that the
equivalent features of the underlying libjpeg API are also working.)
Invoking 'make testclean' or 'nmake testclean' (if using NMake) or building
the 'testclean' target (if using the Visual Studio IDE) will clean up the
output images generated by 'make test'.
On Unix/Linux platforms, more extensive tests of the TurboJPEG/OSS C and Java
wrappers can be run by invoking 'make tjtest'. These extended TurboJPEG tests
essentially iterate through all of the available features of the TurboJPEG APIs
that are not covered by the TurboJPEG unit tests (this includes the lossless
transform options) and compare the images generated by each feature to images
generated using the equivalent feature in the libjpeg API. The extended
TurboJPEG tests are meant to test for regressions in the TurboJPEG wrappers,
not in the underlying libjpeg-turbo library.