The Gordian knot that 7fec5074f9 attempted
to unravel was caused by the fact that there are several
data-precision-dependent (JSAMPLE-dependent) fields and methods in the
exposed libjpeg API structures, and if you change the exposed libjpeg
API structures, then you have to change the whole API. If you change
the whole API, then you have to provide a whole new library to support
the new API, and that makes it difficult to support multiple data
precisions in the same application. (It is not impossible, as example.c
demonstrated, but using data-precision-dependent libjpeg API structures
would have made the cjpeg, djpeg, and jpegtran source code hard to read,
so it made more sense to build, install, and package 12-bit-specific
versions of those applications.)
Unfortunately, the result of that initial integration effort was an
unreadable and unmaintainable mess, which is a problem for a library
that is an ISO/ITU-T reference implementation. Also, as I dug into the
problem of lossless JPEG support, I realized that 16-bit lossless JPEG
images are a thing, and supporting yet another version of the libjpeg
API just for those images is untenable.
In fact, however, the touch points for JSAMPLE in the exposed libjpeg
API structures are minimal:
- The colormap and sample_range_limit fields in jpeg_decompress_struct
- The alloc_sarray() and access_virt_sarray() methods in
jpeg_memory_mgr
- jpeg_write_scanlines() and jpeg_write_raw_data()
- jpeg_read_scanlines() and jpeg_read_raw_data()
- jpeg_skip_scanlines() and jpeg_crop_scanline()
(This is subtle, but both of those functions use JSAMPLE-dependent
opaque structures behind the scenes.)
It is much more readable and maintainable to provide 12-bit-specific
versions of those six top-level API functions and to document that the
aforementioned methods and fields must be type-cast when using 12-bit
samples. Since that eliminates the need to provide a 12-bit-specific
version of the exposed libjpeg API structures, we can:
- Compile only the precision-dependent libjpeg modules (the
coefficient buffer controllers, the colorspace converters, the
DCT/IDCT managers, the main buffer controllers, the preprocessing
and postprocessing controller, the downsampler and upsamplers, the
quantizers, the integer DCT methods, and the IDCT methods) for
multiple data precisions.
- Introduce 12-bit-specific methods into the various internal
structures defined in jpegint.h.
- Create precision-independent data type, macro, method, field, and
function names that are prefixed by an underscore, and use an
internal header to convert those into precision-dependent data
type, macro, method, field, and function names, based on the value
of BITS_IN_JSAMPLE, when compiling the precision-dependent libjpeg
modules.
- Expose precision-dependent jinit*() functions for each of the
precision-dependent libjpeg modules.
- Abstract the precision-dependent libjpeg modules by calling the
appropriate precision-dependent jinit*() function, based on the
value of cinfo->data_precision, from top-level libjpeg API
functions.
- Use the _M_ARM and _M_ARM64 macros provided by Visual Studio for
compile-time detection of Arm builds, since __arm__ and __aarch64__
are only present in GNU-compatible compilers.
- Neon/intrinsics: Use the _CountLeadingZeros() and
_CountLeadingZeros64() intrinsics provided by Visual Studio, since
__builtin_clz() and __builtin_clzl() are only present in
GNU-compatible compilers.
- Neon/intrinsics: Since Visual Studio does not support static vector
initialization, replace static initialization of Neon vectors with the
appropriate intrinsics. Compared to the static initialization
approach, this produces identical assembly code with both GCC and
Clang.
- Neon/intrinsics: Since Visual Studio does not support inline assembly
code, provide alternative code paths for Visual Studio whenever inline
assembly is used.
- Build: Set FLOATTEST appropriately for AArch64 Visual Studio builds
(Visual Studio does not emit fused multiply-add [FMA] instructions by
default for such builds.)
- Neon/intrinsics: Move temporary buffer allocation outside of nested
loops. Since Visual Studio configures Arm builds with a relatively
small amount of stack memory, attempting to allocate those buffers
within the inner loops caused a stack overflow.
Closes#461Closes#475
This commit modifies h1v2_fancy_upsample() so that it uses an ordered
dither pattern, similar to that of h2v1_fancy_upsample(), rounding up or
down the result for alternate pixels rather than always rounding down.
This ensures that the decompression error pattern for a 4:4:0 JPEG image
will be similar to the rotated decompression error pattern for a 4:2:2
JPEG image. Thus, the final result will be similar regardless of
whether a 4:2:2 JPEG image is rotated or transposed before or after
decompression.
Closes#356
libjpeg-turbo has never really supported such compilers, since (AFAIK)
they are non-existent on any modern computing platform and thus
impossible for us to test. (Also, the TurboJPEG API would break without
unsigned chars.)
Furthermore, the unified CMake-based build system introduced in 2.0
always defines HAVE_UNSIGNED_CHAR, so retaining other code paths is
pointless. Eliminating support for compilers without unsigned char
eliminates the need for the GETJSAMPLE() macro, which improves the
readability of many parts of the code as well as improving the
performance of writing Targa and Windows BMP files.
Fixes#317
With rare exceptions ...
- Always separate line continuation characters by one space from
preceding code.
- Always use two-space indentation. Never use tabs.
- Always use K&R-style conditional blocks.
- Always surround operators with spaces, except in raw assembly code.
- Always put a space after, but not before, a comma.
- Never put a space between type casts and variables/function calls.
- Never put a space between the function name and the argument list in
function declarations and prototypes.
- Always surround braces ('{' and '}') with spaces.
- Always surround statements (if, for, else, catch, while, do, switch)
with spaces.
- Always attach pointer symbols ('*' and '**') to the variable or
function name.
- Always precede pointer symbols ('*' and '**') by a space in type
casts.
- Use the MIN() macro from jpegint.h within the libjpeg and TurboJPEG
API libraries (using min() from tjutil.h is still necessary for
TJBench.)
- Where it makes sense (particularly in the TurboJPEG code), put a blank
line after variable declaration blocks.
- Always separate statements in one-liners by two spaces.
The purpose of this was to ease maintenance on my part and also to make
it easier for contributors to figure out how to format patch
submissions. This was admittedly confusing (even to me sometimes) when
we had 3 or 4 different style conventions in the same source tree. The
new convention is more consistent with the formatting of other OSS code
bases.
This commit corrects deviations from the chosen formatting style in the
libjpeg API code and reformats the TurboJPEG API code such that it
conforms to the same standard.
NOTES:
- Although it is no longer necessary for the function name in function
declarations to begin in Column 1 (this was historically necessary
because of the ansi2knr utility, which allowed libjpeg to be built
with non-ANSI compilers), we retain that formatting for the libjpeg
code because it improves readability when using libjpeg's function
attribute macros (GLOBAL(), etc.)
- This reformatting project was accomplished with the help of AStyle and
Uncrustify, although neither was completely up to the task, and thus
a great deal of manual tweaking was required. Note to developers of
code formatting utilities: the libjpeg-turbo code base is an
excellent test bed, because AFAICT, it breaks every single one of the
utilities that are currently available.
- The legacy (MMX, SSE, 3DNow!) assembly code for i386 has been
formatted to match the SSE2 code (refer to
ff5685d5344273df321eb63a005eaae19d2496e3.) I hadn't intended to
bother with this, but the Loongson MMI implementation demonstrated
that there is still academic value to the MMX implementation, as an
algorithmic model for other 64-bit vector implementations. Thus, it
is desirable to improve its readability in the same manner as that of
the SSE2 implementation.
This allows fancy upsampling to be used when decompressing 4:2:2 images
that have been losslessly rotated or transposed.
(docs and comments added by DRC)
Based on f63aca945dCloses#89
The IJG convention is to format copyright notices as:
Copyright (C) YYYY, Owner.
We try to maintain this convention for any code that is part of the
libjpeg API library (with the exception of preserving the copyright
notices from Cendio's code verbatim, since those predate
libjpeg-turbo.)
Note that the phrase "All Rights Reserved" is no longer necessary, since
all Buenos Aires Convention signatories signed onto the Berne Convention
in 2000. However, our convention is to retain this phrase for any files
that have a self-contained copyright header but to leave it off of any
files that refer to another file for conditions of distribution and use.
For instance, all of the non-SIMD files in the libjpeg API library refer
to README.ijg, and the copyright message in that file contains "All
Rights Reserved", so it is unnecessary to add it to the individual
files.
The TurboJPEG code retains my preferred formatting convention for
copyright notices, which is based on that of VirtualGL (where the
TurboJPEG API originated.)
This, in combination with the existing jpeg_skip_scanlines() function,
provides the ability to crop the image both horizontally and vertically
while decompressing (certain restrictions apply-- see libjpeg.txt.)
This also cleans up the documentation of the line skipping feature and
removes the "strip decompression" feature from djpeg, since the new
cropping feature is a superset of it.
Refer to #34 for discussion.
Closes#34
The convention used by libjpeg:
type * variable;
is not very common anymore, because it looks too much like
multiplication. Some (particularly C++ programmers) prefer to tuck the
pointer symbol against the type:
type* variable;
to emphasize that a pointer to a type is effectively a new type.
However, this can also be confusing, since defining multiple variables
on the same line would not work properly:
type* variable1, variable2; /* Only variable1 is actually a
pointer. */
This commit reformats the entirety of the libjpeg-turbo code base so
that it uses the same code formatting convention for pointers that the
TurboJPEG API code uses:
type *variable1, *variable2;
This seems to be the most common convention among C programmers, and
it is the convention used by other codec libraries, such as libpng and
libtiff.
jinclude.h can't be safely included multiple times, so instead of
including it in the shared (broken-out) headers, it should instead be
included by the source files that include one or more of those headers.
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.
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
