From bddf59a7aeec62f6a27de30316105482bd310829 Mon Sep 17 00:00:00 2001 From: David Schleef Date: Sun, 6 Jun 2010 23:45:10 -0700 Subject: [PATCH] docs: Add notes about Orc integration --- docs/design/Makefile.am | 2 +- docs/design/design-orc-integration.txt | 204 +++++++++++++++++++++++++++++++++ 2 files changed, 205 insertions(+), 1 deletion(-) create mode 100644 docs/design/design-orc-integration.txt diff --git a/docs/design/Makefile.am b/docs/design/Makefile.am index a464e1a..e08df9f 100644 --- a/docs/design/Makefile.am +++ b/docs/design/Makefile.am @@ -1,4 +1,4 @@ SUBDIRS = -EXTRA_DIST = design-decodebin.txt +EXTRA_DIST = design-decodebin.txt design-orc-integration.txt diff --git a/docs/design/design-orc-integration.txt b/docs/design/design-orc-integration.txt new file mode 100644 index 0000000..7dc2794 --- /dev/null +++ b/docs/design/design-orc-integration.txt @@ -0,0 +1,204 @@ + +Orc Integration +=============== + +Sections +-------- + + - About Orc + - Fast memcpy() + - Normal Usage + - Build Process + - Testing + - Orc Limitations + + +About Orc +--------- + +Orc code can be in one of two forms: in .orc files that is converted +by orcc to C code that calls liborc functions, or C code that calls +liborc to create complex operations at runtime. The former is mostly +for functions with predetermined functionality. The latter is for +functionality that is determined at runtime, where writing .orc +functions for all combinations would be prohibitive. Orc also has +a fast memcpy and memset which are useful independently. + + +Fast memcpy() +------------- + +*** This part is not integrated yet. *** + +Orc has built-in functions orc_memcpy() and orc_memset() that work +like memcpy() and memset(). These are meant for large copies only. +A reasonable cutoff for using orc_memcpy() instead of memcpy() is +if the number of bytes is generally greater than 100. DO NOT use +orc_memcpy() if the typical is size is less than 20 bytes, especially +if the size is known at compile time, as these cases are inlined by +the compiler. + +(Example: sys/ximage/ximagesink.c) + +Add $(ORC_CFLAGS) to libgstximagesink_la_CFLAGS and $(ORC_LIBS) to +libgstximagesink_la_LIBADD. Then, in the source file, add: + + #ifdef HAVE_ORC + #include + #else + #define orc_memcpy(a,b,c) memcpy(a,b,c) + #endif + +Then switch relevant uses of memcpy() to orc_memcpy(). + +The above example works whether or not Orc is enabled at compile +time. + + +Normal Usage +------------ + +The following lines are added near the top of Makefile.am for plugins +that use Orc code in .orc files (this is for the volume plugin): + + ORC_BASE=volume + include $(top_srcdir)/common/orc.mk + +Also add the generated source file to the plugin build: + + nodist_libgstvolume_la_SOURCES = $(ORC_SOURCES) + +And of course, add $(ORC_CFLAGS) to libgstvolume_la_CFLAGS, and +$(ORC_LIBS) to libgstvolume_la_LIBADD. + +The value assigned to ORC_BASE does not need to be related to +the name of the plugin. + + +Advanced Usage +-------------- + +The Holy Grail of Orc usage is to programmatically generate Orc code +at runtime, have liborc compile it into binary code at runtime, and +then execute this code. Currently, the best example of this is in +Schroedinger. An example of how this would be used is audioconvert: +given an input format, channel position manipulation, dithering and +quantizing configuration, and output format, a Orc code generator +would create an OrcProgram, add the appropriate instructions to do +each step based on the configuration, and then compile the program. +Sucessfully compiling the program would return a function pointer +that can be called to perform the operation. + +This sort of advanced usage requires structural changes to current +plugins (e.g., audioconvert) and will probably be developed +incrementally. Moreover, if such code is intended to be used without +Orc as strict build/runtime requirement, two codepaths would need to +be developed and tested. For this reason, until GStreamer requires +Orc, I think it's a good idea to restrict such advanced usage to the +cog plugin in -bad, which requires Orc. + + +Build Process +------------- + +The goal of the build process is to make Orc non-essential for most +developers and users. This is not to say you shouldn't have Orc +installed -- without it, you will get slow backup C code, just that +people compiling GStreamer are not forced to switch from Liboil to +Orc immediately. + +With Orc installed, the build process will use the Orc Compiler (orcc) +to convert each .orc file into a temporary C source (tmp-orc.c) and a +temporary header file (${name}orc.h if constructed from ${base}.orc). +The C source file is compiled and linked to the plugin, and the header +file is included by other source files in the plugin. + +If 'make orc-update' is run in the source directory, the files +tmp-orc.c and ${base}orc.h are copied to ${base}orc-dist.c and +${base}orc-dist.h respectively. The -dist.[ch] files are automatically +disted via orc.mk. The -dist.[ch] files should be checked in to +git whenever the .orc source is changed and checked in. Example +workflow: + + edit .orc file + ... make, test, etc. + make orc-update + git add volume.orc volumeorc-dist.c volumeorc-dist.h + git commit + +At 'make dist' time, all of the .orc files are compiled, and then +copied to their -dist.[ch] counterparts, and then the -dist.[ch] +files are added to the dist directory. + +Without Orc installed (or --disable-orc given to configure), the +-dist.[ch] files are copied to tmp-orc.c and ${name}orc.h. When +compiled Orc disabled, DISABLE_ORC is defined in config.h, and +the C backup code is compiled. This backup code is pure C, and +does not include orc headers or require linking against liborc. + +The common/orc.mk build method is limited by the inflexibility of +automake. The file tmp-orc.c must be a fixed filename, using ORC_NAME +to generate the filename does not work because it conflicts with +automake's dependency generation. Building multiple .orc files +is not possible due to this restriction. + + +Testing +------- + +If you create another .orc file, please add it to +tests/orc/Makefile.am. This causes automatic test code to be +generated and run during 'make check'. Each function in the .orc +file is tested by comparing the results of executing the run-time +compiled code and the C backup function. + + +Orc Limitations +--------------- + +audioconvert + + Orc doesn't have a mechanism for generating random numbers, which + prevents its use as-is for dithering. One way around this is to + generate suitible dithering values in one pass, then use those + values in a second Orc-based pass. + + Orc doesn't handle 64-bit float, for no good reason. + + Irrespective of Orc handling 64-bit float, it would be useful to + have a direct 32-bit float to 16-bit integer conversion. + + audioconvert is a good candidate for programmatically generated + Orc code. + + audioconvert enumerates functions in terms of big-endian vs. + little-endian. Orc's functions are "native" and "swapped". + Programmatically generating code removes the need to worry about + this. + + Orc doesn't handle 24-bit samples. Fixing this is not a priority + (for ds). + +videoscale + + Orc doesn't handle horizontal resampling yet. The plan is to add + special sampling opcodes, for nearest, bilinear, and cubic + interpolation. + +videotestsrc + + Lots of code in videotestsrc needs to be reweitten to be SIMD + (and Orc) friendly, e.g., sutff that uses oil_splat_u8(). + + A fast low-quality random number generator in Orc would be useful + here. + +volume + + Many of the comments on audioconvert apply here as well. + + There are a bunch of FIXME's in here that are due to misapplied + patches. + + + -- 2.7.4