Most of these involved overrunning the signed 32-bit JLONG type whenever
building libjpeg-turbo with a 32-bit compiler. These issues are not
believed to represent actual security threats, but eliminating them
makes it easier to detect such threats should they arise in the future.
These days, INT32 is a commonly-defined datatype in system headers. We
cannot eliminate the definition of that datatype from jmorecfg.h, since
the INT32 typedef has technically been part of the libjpeg API since
version 5 (1994.) However, using INT32 internally is risky, because the
inclusion of a particular header (Xmd.h, for instance) could change the
definition of INT32 from long to int on 64-bit platforms and thus change
the internal behavior of libjpeg-turbo in unexpected ways (for instance,
failing to correctly set __INT32_IS_ACTUALLY_LONG to match the INT32
typedef-- perhaps as a result of including the wrong version of
jpeglib.h-- could cause libjpeg-turbo to produce incorrect results.)
The library has always been built in environments in which INT32 is
effectively long (on Windows, long is always 32-bit, so effectively it's
the same as int), so it makes sense to turn INT32 into an explicitly
long datatype. This ensures that libjpeg-turbo will always behave
consistently, regardless of the headers included at compile time.
Addresses a concern expressed in #26.
The IJG README file has been renamed to README.ijg, in order to avoid
confusion (many people were assuming that that was our project's README
file and weren't reading README-turbo.txt) and to lay the groundwork for
markdown versions of the libjpeg-turbo README and build instructions.
With certain images, compressing using quality=100 and the fast integer
forward DCT will cause the divisor passed to compute_reciprocal() to be
1. In those cases, the library already disables the SIMD quantization
algorithm to avoid 16-bit overflow. However, compute_reciprocal()
doesn't properly handle the divisor==1 case, so we need to use special
values in that case so that the C quantization algorithm will behave
like an identity function.
We use the heap allocators to avoid having more than one implementation
of the alignment logic.
git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@19 632fc199-4ca6-4c93-a231-07263d6284db
This has no measurable difference right now but makes it possible to do
SIMD implementations of this stage.
git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@16 632fc199-4ca6-4c93-a231-07263d6284db
Designed to impose minimal changes on the "normal" code.
git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@14 632fc199-4ca6-4c93-a231-07263d6284db
Divide it into sample conversion, DCT and quantization in order to
easily provide alternative implementations of each stage.
git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@13 632fc199-4ca6-4c93-a231-07263d6284db
