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diff --git a/doc/optimization.txt b/doc/optimization.txt new file mode 100644 index 0000000000..18ad2b6283 --- /dev/null +++ b/doc/optimization.txt @@ -0,0 +1,137 @@ +optimization Tips (for libavcodec): + +What to optimize: +if u plan to do non-x86 architecture specific optimiztions (SIMD normally) then +take a look in the i386/ directory, as most important functions are allready +optimized for MMX + +if u want to do x86 optimizations then u can either try to finetune the stuff in the +i386 directory or find some other functions in the c source to optimize, but there +arent many left + +Understanding these overoptimized functions: +as many functions, like the c ones tend to be a bit unreadable currently becouse +of optimizations it is difficult to understand them (and write arichtecture +specific versions, or optimize the c functions further) it is recommanded to look +at older CVS versions of the interresting files (just use CVSWEB at +(http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/ffmpeg/ffmpeg/libavcodec/)) +or perhaps look into the other architecture specific versions in i386/, ppc/, +alpha/, ...; even if u dont understand the instructions exactly it could help +understanding the functions & how they can be optimized + +NOTE:!!! if u still dont understand some function then ask at our mailing list!!! +(http://lists.sourceforge.net/lists/listinfo/ffmpeg-devel) + + + +wtf is that function good for ....: +the primary purpose of that list is to avoid wasting time to optimize functions +which are rarely used + +put(_no_rnd)_pixels{,_x2,_y2,_xy2} + used in motion compensation (en/decoding) + +avg_pixels{,_x2,_y2,_xy2} + used in motion compensation of B Frames + these are less important then the put*pixels functions + +avg_no_rnd_pixels* + unused + +pix_abs16x16{,_x2,_y2,_xy2} + used in motion estimation (encoding) with SAD + +pix_abs8x8{,_x2,_y2,_xy2} + used in motion estimation (encoding) with SAD of MPEG4 4MV only + these are less important then the pix_abs16x16* functions + +put_mspel8_mc* / wmv2_mspel8* + used only in WMV2 + it is not recommanded that u waste ur time with these, as WMV2 is a + ugly and relativly useless codec + +mpeg4_qpel* / *qpel_mc* + use in MPEG4 qpel Motion compensation (encoding & decoding) + the qpel8 functions are used only for 4mv + the avg_* functions are used only for b frames + optimizing them should have a significant impact on qpel encoding & decoding + +qpel{8,16}_mc??_old_c / *pixels{8,16}_l4 + just used to workaround a bug in old libavcodec encoder + dont optimze them + +add_bytes/diff_bytes + for huffyuv only, optimize if u want a faster ff-huffyuv codec + +get_pixels / diff_pixels + used for encoding, easy + +clear_blocks + easiest, to optimize + +gmc + used for mpeg4 gmc + optimizing this should have a significant effect on the gmc decoding speed but + its very likely impossible to write in SIMD + +pix_sum + used for encoding + +hadamard8_diff / sse / sad == pix_norm1 / dct_sad / quant_psnr + specific compare functions used in encoding, it depends upon the command line + switches which of these are used + dont waste ur time with dct_sad & quant_psnr they arent really usefull + +put_pixels_clamped / add_pixels_clamped + used for en/decoding, easy + +idct/fdct + idct (encoding & decoding) + fdct (encoding) + difficult to optimize + +dct_quantize_trellis + used for encoding with trellis quantization + difficult to optimize + +dct_quantize + used for encoding + +dct_unquantize_mpeg1 + used in mpeg1 en/decoding + +dct_unquantize_mpeg2 + used in mpeg2 en/decoding + +dct_unquantize_h263 + used in mpeg4/h263 en/decoding + +FIXME remaining functions? +btw, most of these are in dsputil.c/.h some are in mpegvideo.c/.h + + + +Alignment: +some instructions on some architectures have strict alignment restrictions, +for example most SSE/SSE2 inctructios on X86 +the minimum guranteed alignment is writen in the .h files +for example: + void (*put_pixels_clamped)(const DCTELEM *block/*align 16*/, UINT8 *pixels/*align 8*/, int line_size); + + + +Links: +X86 specific: +http://developer.intel.com/design/pentium4/manuals/248966.htm + +The IA-32 Intel Architecture Software Developer's Manual, Volume 2: +Instruction Set Reference +http://developer.intel.com/design/pentium4/manuals/245471.htm + +http://www.agner.org/assem/ + +AMD Athlon Processor x86 Code Optimization Guide: +http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/22007.pdf + +GCC asm links: +FIXME
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