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Diffstat (limited to 'src/3rdparty/libjpeg/src/README.md')
| -rw-r--r-- | src/3rdparty/libjpeg/src/README.md | 28 |
1 files changed, 19 insertions, 9 deletions
diff --git a/src/3rdparty/libjpeg/src/README.md b/src/3rdparty/libjpeg/src/README.md index a769259891..c61b855644 100644 --- a/src/3rdparty/libjpeg/src/README.md +++ b/src/3rdparty/libjpeg/src/README.md @@ -135,12 +135,11 @@ without recompiling. libjpeg-turbo does not claim to support all of the libjpeg v7+ features, nor to produce identical output to libjpeg v7+ in all cases (see below.) -By passing an argument of `--with-jpeg7` or `--with-jpeg8` to `configure`, or -an argument of `-DWITH_JPEG7=1` or `-DWITH_JPEG8=1` to `cmake`, you can build a -version of libjpeg-turbo that emulates the libjpeg v7 or v8 ABI, so that -programs that are built against libjpeg v7 or v8 can be run with libjpeg-turbo. -The following section describes which libjpeg v7+ features are supported and -which aren't. +By passing an argument of `-DWITH_JPEG7=1` or `-DWITH_JPEG8=1` to `cmake`, you +can build a version of libjpeg-turbo that emulates the libjpeg v7 or v8 ABI, so +that programs that are built against libjpeg v7 or v8 can be run with +libjpeg-turbo. The following section describes which libjpeg v7+ features are +supported and which aren't. ### Support for libjpeg v7 and v8 Features @@ -247,9 +246,8 @@ don't, and it allows those functions to be provided in the "official" libjpeg-turbo binaries. Those who are concerned about maintaining strict conformance with the libjpeg -v6b or v7 API can pass an argument of `--without-mem-srcdst` to `configure` or -an argument of `-DWITH_MEM_SRCDST=0` to `cmake` prior to building -libjpeg-turbo. This will restore the pre-1.3 behavior, in which +v6b or v7 API can pass an argument of `-DWITH_MEM_SRCDST=0` to `cmake` prior to +building libjpeg-turbo. This will restore the pre-1.3 behavior, in which `jpeg_mem_src()` and `jpeg_mem_dest()` are only included when emulating the libjpeg v8 API/ABI. @@ -344,3 +342,15 @@ quality of 98-100. Thus, libjpeg-turbo must use the non-SIMD quantization function in those cases. This causes performance to drop by as much as 40%. It is therefore strongly advised that you use the slow integer forward DCT whenever encoding images with a JPEG quality of 98 or higher. + + +Memory Debugger Pitfalls +======================== + +Valgrind and Memory Sanitizer (MSan) can generate false positives +(specifically, incorrect reports of uninitialized memory accesses) when used +with libjpeg-turbo's SIMD extensions. It is generally recommended that the +SIMD extensions be disabled, either by passing an argument of `-DWITH_SIMD=0` +to `cmake` when configuring the build or by setting the environment variable +`JSIMD_FORCENONE` to `1` at run time, when testing libjpeg-turbo with Valgrind, +MSan, or other memory debuggers. |