The primary purpose of this is to encourage adoption of libjpeg-turbo in
downstream Windows projects that forbid the use of "deprecated"
functions. libjpeg-turbo's usage of those functions was not actually
unsafe, because:
- libjpeg-turbo always checks the return value of fopen() and ensures
that a NULL filename can never be passed to it.
- libjpeg-turbo always checks the return value of getenv() and never
passes a NULL argument to it.
- The sprintf() calls in format_message() (jerror.c) could never
overflow the destination string buffer or leave it unterminated as
long as the buffer was at least JMSG_LENGTH_MAX bytes in length, as
instructed. (Regardless, this commit replaces those calls with
snprintf() calls.)
- libjpeg-turbo never uses sscanf() to read strings or multi-byte
character arrays.
- Because of b7d6e84d6a, wrjpgcom
explicitly checks the bounds of the source and destination strings
before calling strcat() and strcpy().
- libjpeg-turbo always ensures that the destination string is
terminated when using strncpy().
(548490fe5e made this explicit.)
Regarding thread safety:
Technically speaking, getenv() is not thread-safe, because the returned
pointer may be invalidated if another thread sets the same environment
variable between the time that the first thread calls getenv() and the
time that that thread uses the return value. In practice, however, this
could only occur with libjpeg-turbo if:
(1) A multithreaded calling application used the deprecated and
undocumented TJFLAG_FORCEMMX/TJFLAG_FORCESSE/TJFLAG_FORCESSE2 flags in
the TurboJPEG API or set one of the corresponding environment variables
(which are only intended for testing purposes.) Since the TurboJPEG API
library only ever passed string constants to putenv(), the only inherent
risk (i.e. the only risk introduced by the library and not the calling
application) was that the SIMD extensions may have read an incorrect
value from one of the aforementioned environment variables.
or
(2) A multithreaded calling application modified the value of the
JPEGMEM environment variable in one thread while another thread was
reading the value of that environment variable (in the body of
jpeg_create_compress() or jpeg_create_decompress().) Given that the
libjpeg API provides a thread-safe way for applications to modify the
default memory limit without using the JPEGMEM environment variable,
direct modification of that environment variable by calling applications
is not supported.
Microsoft's implementation of getenv_s() does not claim to be
thread-safe either, so this commit uses getenv_s() solely to mollify
Visual Studio. New inline functions and macros (GETENV_S() and
PUTENV_S) wrap getenv_s()/_putenv_s() when building for Visual Studio
and getenv()/setenv() otherwise, but GETENV_S()/PUTENV_S() provide no
advantages over getenv()/setenv() other than parameter validation. They
are implemented solely for convenience.
Technically speaking, strerror() is not thread-safe, because the
returned pointer may be invalidated if another thread changes the locale
and/or calls strerror() between the time that the first thread calls
strerror() and the time that that thread uses the return value. In
practice, however, this could only occur with libjpeg-turbo if a
multithreaded calling application encountered a file I/O error in
tjLoadImage() or tjSaveImage(). Since both of those functions
immediately copy the string returned from strerror() into a thread-local
buffer, the risk is minimal, and the worst case would involve an
incorrect error string being reported to the calling application.
Regardless, this commit uses strerror_s() in the TurboJPEG API library
when building for Visual Studio. Note that strerror_r() could have been
used on Un*x systems, but it would have been necessary to handle both
the POSIX and GNU implementations of that function and perform
widespread compatibility testing. Such is left as an exercise for
another day.
Fixes#568
There was no previous GAS implementation.
NOTE: This doesn't produce much of a speedup when using -O3, because -O3
already enables Neon autovectorization, which works well for the scalar
C implementation of plain upsampling. However, the Neon SIMD
implementation will benefit other optimization levels.
There was no previous GAS implementation.
This commit also reverts 40557b2301 and
7723d7f7d0.
7723d7f7d0 was only necessary because
there was no Neon implementation of merged upsampling/color conversion,
and 40557b2301 was only necessary because
of 7723d7f7d0.
The previous AArch32 GAS implementation of h2v1 fancy upsampling has
been removed, since the intrinsics implementation provides the same or
better performance. There was no previous GAS implementation of h2v2
fancy upsampling, and there was no previous AArch64 GAS implementation
of h2v1 fancy upsampling.
The previous AArch64 GAS implementation is retained by default when
using GCC, in order to avoid a performance regression. The intrinsics
implementation can be forced on or off using the new NEON_INTRINSICS
CMake variable. The previous AArch32 GAS implementation has been
removed, since the intrinsics implementation provides the same or better
performance.
The previous AArch64 GAS implementation is retained by default when
using GCC, in order to avoid a performance regression. The intrinsics
implementation can be forced on or off using the new NEON_INTRINSICS
CMake variable. The previous AArch32 GAS implementation has been
removed, since the intrinsics implementation provides the same or better
performance.
The previous AArch32 and AArch64 GAS implementations are retained by
default when using GCC, in order to avoid a performance regression. The
intrinsics implementation can be forced on or off using a new
NEON_INTRINSICS CMake variable.
