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 DSPr2 code was errantly comparing the residual (t9, width & 0xF)
with the end pointer (t4, out + width) instead of the width directly
(a1). This would give the wrong results with any image whose output
width was less than 16. The other small changes (ulw to lw and removal
of the nop) are just some easy optimizations around this code.
This issue caused a buffer overrun and subsequent segfault on images
whose scaled output height was 1 pixel and whose scaled output width was
< 16 pixels. Note that the "plain" (non-fancy and non-merged) upsample
routine, which was affected by this bug, is normally not used except
when decompressing a non-YCbCr JPEG image, but it is also used when
decompressing a single-row image (because the other upsampling
algorithms require at least two rows.)
Closes#16.
When compiled with -mfpxx (which is now the default on Debian), there are
some restrictions on the use of odd-numbered FP registers. More details
about FPXX can be found here:
https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking
This commit simply changes all uses of FP registers to an even-numbered
equivalent like this:
f0 -> f0
f1 -> f2
f2 -> f4
...
f8 -> f16
This commit should have no observable effect except that the MIPS assembly
will now compile with -mfpxx.
Closes#11
