Update libjpeg-turbo.

README-turbo.txt

 *******************************************************************************
 **     Background
 *******************************************************************************
 
 libjpeg-turbo is a derivative of libjpeg that uses SIMD instructions (MMX,
-SSE2, etc.) to accelerate baseline JPEG compression and decompression on x86
-and x86-64 systems.  On such systems, libjpeg-turbo is generally 2-4x as fast
-as the unmodified version of libjpeg, all else being equal.
+SSE2, NEON) to accelerate baseline JPEG compression and decompression on x86,
+x86-64, and ARM systems.  On such systems, libjpeg-turbo is generally 2-4x as
+fast as the unmodified version of libjpeg, all else being equal.
 
 libjpeg-turbo was originally based on libjpeg/SIMD by Miyasaka Masaru, but
 the TigerVNC and VirtualGL projects made numerous enhancements to the codec in
 2009, including improved support for Mac OS X, 64-bit support, support for
-32-bit and big endian pixel formats (RGBX, XBGR, etc.), accelerated Huffman
-encoding/decoding, and various bug fixes.  The goal was to produce a fully open
-source codec that could replace the partially closed source TurboJPEG/IPP codec
-used by VirtualGL and TurboVNC.  libjpeg-turbo generally performs in the range
-of 80-120% of TurboJPEG/IPP.  It is faster in some areas but slower in others.
+32-bit and big-endian pixel formats (RGBX, XBGR, etc.), accelerated Huffman
+encoding/decoding, and various bug fixes.  The goal was to produce a fully
+open-source codec that could replace the partially closed-source TurboJPEG/IPP
+codec used by VirtualGL and TurboVNC.  libjpeg-turbo generally achieves 80-120%
+of the performance of TurboJPEG/IPP.  It is faster in some areas but slower in
+others.
 
 In early 2010, libjpeg-turbo spun off into its own independent project, with
 the goal of making high-speed JPEG compression/decompression technology
-available to a broader range of users and developers.  The libjpeg-turbo shared
-libraries can be used as drop-in replacements for libjpeg on most systems.
+available to a broader range of users and developers.
 
 
 *******************************************************************************
 **     License
 *******************************************************************************
 
-libjpeg-turbo is licensed under a non-restrictive, BSD-style license
-(see README.)  The TurboJPEG/OSS wrapper (both C and Java versions) and
+Most of libjpeg-turbo inherits the non-restrictive, BSD-style license used by
+libjpeg (see README.)  The TurboJPEG/OSS wrapper (both C and Java versions) and
 associated test programs bear a similar license, which is reproduced below:
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met:
 
 - Redistributions of source code must retain the above copyright notice,
   this list of conditions and the following disclaimer.
 - Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.
@@ skipping 14 matching lines @@
 POSSIBILITY OF SUCH DAMAGE.
 
 
 *******************************************************************************
 **     Using libjpeg-turbo
 *******************************************************************************
 
 libjpeg-turbo includes two APIs that can be used to compress and decompress
 JPEG images:
 
-  TurboJPEG/OSS:  This API wraps libjpeg-turbo and provides an easy-to-use
-  interface for compressing and decompressing JPEG images in memory.  It also
-  provides some features that would not be straightforward to implement using
-  the underlying libjpeg API, such as generating planar YUV images and
-  performing multiple simultaneous lossless transforms on an image.  The Java
-  interface for libjpeg-turbo is written on top of TurboJPEG/OSS.
+  TurboJPEG API:  This API provides an easy-to-use interface for compressing
+  and decompressing JPEG images in memory.  It also provides some functionality
+  that would not be straightforward to achieve using the underlying libjpeg
+  API, such as generating planar YUV images and performing multiple
+  simultaneous lossless transforms on an image.  The Java interface for
+  libjpeg-turbo is written on top of the TurboJPEG API.
 
-  libjpeg API:  This is the industry standard API for compressing and
-  decompressing JPEG images.  It is more difficult to use than TurboJPEG/OSS
-  but also more powerful.  libjpeg-turbo is both API/ABI-compatible and
+  libjpeg API:  This is the de facto industry-standard API for compressing and
+  decompressing JPEG images.  It is more difficult to use than the TurboJPEG
+  API but also more powerful.  libjpeg-turbo is both API/ABI-compatible and
   mathematically compatible with libjpeg v6b.  It can also optionally be
   configured to be API/ABI-compatible with libjpeg v7 and v8 (see below.)
 
 
 =============================
 Replacing libjpeg at Run Time
 =============================
 
 If a Unix application is dynamically linked with libjpeg, then you can replace
 libjpeg with libjpeg-turbo at run time by manipulating LD_LIBRARY_PATH.
 For instance:
 
   [Using libjpeg]
   > time cjpeg <vgl_5674_0098.ppm >vgl_5674_0098.jpg
   real  0m0.392s
   user  0m0.074s
   sys   0m0.020s
 
   [Using libjpeg-turbo]
   > export LD_LIBRARY_PATH=/opt/libjpeg-turbo/{lib}:$LD_LIBRARY_PATH
   > time cjpeg <vgl_5674_0098.ppm >vgl_5674_0098.jpg
   real  0m0.109s
   user  0m0.029s
   sys   0m0.010s
 
 NOTE: {lib} can be lib, lib32, lib64, or lib/64, depending on the O/S and
 architecture.
 
 System administrators can also replace the libjpeg sym links in /usr/{lib} with
-links to the libjpeg dynamic library located in /opt/libjpeg-turbo/{lib}.  This
-will effectively accelerate every dynamically linked libjpeg application on the
-system.
+links to the libjpeg-turbo dynamic library located in /opt/libjpeg-turbo/{lib}.
+This will effectively accelerate every application that uses the libjpeg
+dynamic library on the system.
 
 The libjpeg-turbo SDK for Visual C++ installs the libjpeg-turbo DLL
-(jpeg62.dll, jpeg7.dll, or jpeg8.dll, depending on whether libjpeg v6b, v7, or
-v8 emulation is enabled) into c:\libjpeg-turbo[64]\bin, and the PATH
+(jpeg62.dll, jpeg7.dll, or jpeg8.dll, depending on whether it was built with
+libjpeg v6b, v7, or v8 emulation) into c:\libjpeg-turbo[64]\bin, and the PATH
 environment variable can be modified such that this directory is searched
 before any others that might contain a libjpeg DLL.  However, if a libjpeg
 DLL exists in an application's install directory, then Windows will load this
 DLL first whenever the application is launched.  Thus, if an application ships
 with jpeg62.dll, jpeg7.dll, or jpeg8.dll, then back up the application's
 version of this DLL and copy c:\libjpeg-turbo[64]\bin\jpeg*.dll into the
 application's install directory to accelerate it.
 
 The version of the libjpeg-turbo DLL distributed in the libjpeg-turbo SDK for
-Visual C++ requires the Visual C++ 2008 C run time DLL (msvcr90.dll).
+Visual C++ requires the Visual C++ 2008 C run-time DLL (msvcr90.dll).
 msvcr90.dll ships with more recent versions of Windows, but users of older
 Windows releases can obtain it from the Visual C++ 2008 Redistributable
 Package, which is available as a free download from Microsoft's web site.
 
-NOTE:  Features of libjpeg that require passing a C run time structure, such
+NOTE:  Features of libjpeg that require passing a C run-time structure, such
 as a file handle, from an application to libjpeg will probably not work with
 the version of the libjpeg-turbo DLL distributed in the libjpeg-turbo SDK for
 Visual C++, unless the application is also built to use the Visual C++ 2008 C
-run time DLL.  In particular, this affects jpeg_stdio_dest() and
+run-time DLL.  In particular, this affects jpeg_stdio_dest() and
 jpeg_stdio_src().
 
 Mac applications typically embed their own copies of the libjpeg dylib inside
 the (hidden) application bundle, so it is not possible to globally replace
 libjpeg on OS X systems.  If an application uses a shared library version of
 libjpeg, then it may be possible to replace the application's version of it.
 This would generally involve copying libjpeg.*.dylib from libjpeg-turbo into
 the appropriate place in the application bundle and using install_name_tool to
 repoint the dylib to the new directory.  This requires an advanced knowledge of
 OS X and would not survive an upgrade or a re-install of the application.
 Thus, it is not recommended for most users.
 
 =======================
 Replacing TurboJPEG/IPP
 =======================
 
 libjpeg-turbo is a drop-in replacement for the TurboJPEG/IPP SDK used by
 VirtualGL 2.1.x and TurboVNC 0.6 (and prior.)  libjpeg-turbo contains a wrapper
 library (TurboJPEG/OSS) that emulates the TurboJPEG API using libjpeg-turbo
-instead of the closed source Intel Performance Primitives.  You can replace the
+instead of the closed-source Intel Performance Primitives.  You can replace the
 TurboJPEG/IPP package on Linux systems with the libjpeg-turbo package in order
 to make existing releases of VirtualGL 2.1.x and TurboVNC 0.x use the new codec
 at run time.  Note that the 64-bit libjpeg-turbo packages contain only 64-bit
 binaries, whereas the TurboJPEG/IPP 64-bit packages contained both 64-bit and
 32-bit binaries.  Thus, to replace a TurboJPEG/IPP 64-bit package, install
 both the 64-bit and 32-bit versions of libjpeg-turbo.
 
 You can also build the VirtualGL 2.1.x and TurboVNC 0.6 source code with
 the libjpeg-turbo SDK instead of TurboJPEG/IPP.  It should work identically.
 libjpeg-turbo also includes static library versions of TurboJPEG/OSS, which
-are used to build TurboVNC 1.0 and later.
+are used to build VirtualGL 2.2 and TurboVNC 1.0 and later.
 
 ========================================
 Using libjpeg-turbo in Your Own Programs
 ========================================
 
 For the most part, libjpeg-turbo should work identically to libjpeg, so in
 most cases, an application can be built against libjpeg and then run against
 libjpeg-turbo.  On Unix systems (including Cygwin), you can build against
 libjpeg-turbo instead of libjpeg by setting
 
@@ skipping 78 matching lines @@
 
   #ifdef JCS_ALPHA_EXTENSIONS
 
 jcstest.c, located in the libjpeg-turbo source tree, demonstrates how to check
 for the existence of the colorspace extensions at compile time and run time.
 
 =================================
 libjpeg v7 and v8 API/ABI support
 =================================
 
-libjpeg v7 and v8 added new features to the API/ABI, and, unfortunately, the
-compression and decompression structures were extended in a backward-
-incompatible manner to accommodate these features.  Thus, programs that are
+With libjpeg v7 and v8, new features were added that necessitated extending the
+compression and decompression structures.  Unfortunately, due to the exposed
+nature of those structures, extending them also necessitated breaking backward
+ABI compatibility with previous libjpeg releases.  Thus, programs that are
 built to use libjpeg v7 or v8 did not work with libjpeg-turbo, since it is
 based on the libjpeg v6b code base.  Although libjpeg v7 and v8 are still not
 as widely used as v6b, enough programs (including a few Linux distros) have
 made the switch that it was desirable to provide support for the libjpeg v7/v8
-API/ABI in libjpeg-turbo.
-
-Some of the libjpeg v7 and v8 features -- DCT scaling, to name one -- involve
-deep modifications to the code that cannot be accommodated by libjpeg-turbo
-without either breaking compatibility with libjpeg v6b or producing an
-unsupportable mess.  In order to fully support libjpeg v8 with all of its
-features, we would have to essentially port the SIMD extensions to the libjpeg
-v8 code base and maintain two separate code trees.  We are hesitant to do this
-until/unless the newer libjpeg code bases garner more community support and
-involvement and until/unless we have some notion of whether future libjpeg
-releases will also be backward-incompatible.
+API/ABI in libjpeg-turbo.  Although libjpeg-turbo can now be configured as a
+drop-in replacement for libjpeg v7 or v8, it should be noted that not all of
+the features in libjpeg v7 and v8 are supported (see below.)
 
 By passing an argument of --with-jpeg7 or --with-jpeg8 to configure, or an
 argument of -DWITH_JPEG7=1 or -DWITH_JPEG8=1 to cmake, you can build a version
 of libjpeg-turbo that emulates the libjpeg v7 or v8 API/ABI, so that programs
 that are built against libjpeg v7 or v8 can be run with libjpeg-turbo.  The
 following section describes which libjpeg v7+ features are supported and which
 aren't.
 
 libjpeg v7 and v8 Features:
 ---------------------------
 
 Fully supported:
 
 -- cjpeg: Separate quality settings for luminance and chrominance
    Note that the libpjeg v7+ API was extended to accommodate this feature only
    for convenience purposes.  It has always been possible to implement this
    feature with libjpeg v6b (see rdswitch.c for an example.)
 
+-- libjpeg: IDCT scaling extensions in decompressor
+   libjpeg-turbo supports IDCT scaling with scaling factors of 1/8, 1/4, 3/8,
+   1/2, 5/8, 3/4, 7/8, 9/8, 5/4, 11/8, 3/2, 13/8, 7/4, 15/8, and 2/1 (only 1/4
+   and 1/2 are SIMD-accelerated.)
+
 -- cjpeg: 32-bit BMP support
 
 -- jpegtran: lossless cropping
 
 -- jpegtran: -perfect option
 
 -- rdjpgcom: -raw option
 
 -- rdjpgcom: locale awareness
 
 
 Fully supported when using libjpeg v7/v8 emulation:
 
 -- libjpeg: In-memory source and destination managers
 
 
 Not supported:
 
 -- libjpeg: DCT scaling in compressor
    cinfo.scale_num and cinfo.scale_denom are silently ignored.
+   There is no technical reason why DCT scaling cannot be supported, but
+   without the SmartScale extension (see below), it would only be able to
+   down-scale using ratios of 1/2, 8/15, 4/7, 8/13, 2/3, 8/11, 4/5, and 8/9,
+   which is of limited usefulness.
 
--- libjpeg: IDCT scaling extensions in decompressor
-   libjpeg-turbo still supports IDCT scaling with scaling factors of 1/2, 1/4,
-   and 1/8 (same as libjpeg v6b.)
+-- libjpeg: SmartScale
+   cinfo.block_size is silently ignored.
+   SmartScale is an extension to the JPEG format that allows for DCT block
+   sizes other than 8x8.  It would be difficult to support this feature while
+   retaining backward compatibility with libjpeg v6b.
 
 -- libjpeg: Fancy downsampling in compressor
    cinfo.do_fancy_downsampling is silently ignored.
+   This requires the DCT scaling feature, which is not supported.
 
 -- jpegtran: Scaling
-   Seems to depend on the DCT scaling feature, which isn't supported.
+   This requires both the DCT scaling and SmartScale features, which are not
+   supported.
+
+-- Lossless RGB JPEG files
+   This requires the SmartScale feature, which is not supported.
 
 
 *******************************************************************************
 **     Performance pitfalls
 *******************************************************************************
 
 ===============
 Restart Markers
 ===============
 
 The optimized Huffman decoder in libjpeg-turbo does not handle restart markers
-in a way that makes libjpeg happy, so it is necessary to use the slow Huffman
-decoder when decompressing a JPEG image that has restart markers.  This can
-cause the decompression performance to drop by as much as 20%, but the
-performance will still be much much greater than that of libjpeg v6b.  Many
-consumer packages, such as PhotoShop, use restart markers when generating JPEG
-images, so images generated by those programs will experience this issue.
+in a way that makes the rest of the libjpeg infrastructure happy, so it is
+necessary to use the slow Huffman decoder when decompressing a JPEG image that
+has restart markers.  This can cause the decompression performance to drop by
+as much as 20%, but the performance will still be much greater than that of
+libjpeg.  Many consumer packages, such as PhotoShop, use restart markers when
+generating JPEG images, so images generated by those programs will experience
+this issue.
 
 ===============================================
 Fast Integer Forward DCT at High Quality Levels
 ===============================================
 
 The algorithm used by the SIMD-accelerated quantization function cannot produce
 correct results whenever the fast integer forward DCT is used along with a JPEG
 quality of 98-100.  Thus, libjpeg-turbo must use the non-SIMD quantization
 function in those cases.  This causes performance to drop by as much as 40%.
 It is therefore strongly advised that you use the slow integer forward DCT
 whenever encoding images with a JPEG quality of 98 or higher.