byte, word, dword, qword, oword, and yword are all assembler keywords,
so it makes sense to use lowercase for these so as not to mistake them
for macros or constants.
The old Un*x (autotools-based) build system always auto-generated this
file, but that behavior was more or less a relic of the days before the
libjpeg-turbo colorspace extensions were implemented. The thinking was
that, if a particular developer wanted to change RGB_RED, RGB_GREEN,
RGB_BLUE, or RGB_PIXELSIZE in order to compress from/decompress to
different RGB pixel layouts, then the SIMD extensions should
automatically respond to those changes whenever they were made to
jmorecfg.h. The modern reality is that changing RGB_* is no longer
necessary because of the libjpeg-turbo colorspace extensions, and
changing any of the other constants in jsimdcfg.inc can't be done
without making deeper modifications to the SIMD extensions. In general,
we treat RGB_* as a de facto, immutable part of the legacy libpjeg API.
Realistically, since the values of those constants have been the same in
every Un*x distribution released in the past 20-30 years, any software
that uses a system-supplied build of libjpeg must assume that those
constants will have default values.
Furthermore, even if it made sense to auto-generate jsimdcfg.inc, it was
never possible to do so on Windows, so it was always going to be
necessary to manually generate the Windows version of the file whenever
any of the constants changed. This commit introduces a new custom CMake
target called "jsimdcfg" that can be used, on Un*x platforms, to
generate jsimdcfg.inc on demand, although this should only be necessary
when introducing new x86 SIMD instructions or making other deep
modifications, such as SIMD acceleration for 12-bit JPEGs.
For those who may be wondering why we don't do the same thing for
win/jconfig.h.in, it's because performing all of the necessary CMake
checks to populate that file is very slow on Windows.
Within the libjpeg API code, it seems to be more the convention than not
to separate the macro name and value by two or more spaces, which
improves general readability. Making this consistent across all of
libjpeg-turbo is less about my individual preferences and more about
making it easy to automatically detect variations from our chosen
formatting convention. I intend to release the script I'm using to
validate this stuff, once it matures and stabilizes a bit.
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.
