1 optimization Tips (for libavcodec):
4 if u plan to do non-x86 architecture specific optimiztions (SIMD normally) then
5 take a look in the i386/ directory, as most important functions are allready
8 if u want to do x86 optimizations then u can either try to finetune the stuff in the
9 i386 directory or find some other functions in the c source to optimize, but there
12 Understanding these overoptimized functions:
13 as many functions, like the c ones tend to be a bit unreadable currently becouse
14 of optimizations it is difficult to understand them (and write arichtecture
15 specific versions, or optimize the c functions further) it is recommanded to look
16 at older CVS versions of the interresting files (just use CVSWEB at
17 (http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/ffmpeg/ffmpeg/libavcodec/))
18 or perhaps look into the other architecture specific versions in i386/, ppc/,
19 alpha/, ...; even if u dont understand the instructions exactly it could help
20 understanding the functions & how they can be optimized
22 NOTE:!!! if u still dont understand some function then ask at our mailing list!!!
23 (http://lists.sourceforge.net/lists/listinfo/ffmpeg-devel)
27 wtf is that function good for ....:
28 the primary purpose of that list is to avoid wasting time to optimize functions
31 put(_no_rnd)_pixels{,_x2,_y2,_xy2}
32 used in motion compensation (en/decoding)
34 avg_pixels{,_x2,_y2,_xy2}
35 used in motion compensation of B Frames
36 these are less important then the put*pixels functions
41 pix_abs16x16{,_x2,_y2,_xy2}
42 used in motion estimation (encoding) with SAD
44 pix_abs8x8{,_x2,_y2,_xy2}
45 used in motion estimation (encoding) with SAD of MPEG4 4MV only
46 these are less important then the pix_abs16x16* functions
48 put_mspel8_mc* / wmv2_mspel8*
50 it is not recommanded that u waste ur time with these, as WMV2 is a
51 ugly and relativly useless codec
53 mpeg4_qpel* / *qpel_mc*
54 use in MPEG4 qpel Motion compensation (encoding & decoding)
55 the qpel8 functions are used only for 4mv
56 the avg_* functions are used only for b frames
57 optimizing them should have a significant impact on qpel encoding & decoding
59 qpel{8,16}_mc??_old_c / *pixels{8,16}_l4
60 just used to workaround a bug in old libavcodec encoder
64 for huffyuv only, optimize if u want a faster ff-huffyuv codec
66 get_pixels / diff_pixels
67 used for encoding, easy
74 optimizing this should have a significant effect on the gmc decoding speed but
75 its very likely impossible to write in SIMD
78 used for chroma blocks in mpeg4 gmc with 1 warp point
79 (there are 4 luma & 2 chroma blocks per macrobock, so
80 only 1/3 of the gmc blocks use this, the other 2/3
81 use the normal put_pixel* code, but only if there is
83 Note: Divx5 gmc always uses just 1 warp point
88 hadamard8_diff / sse / sad == pix_norm1 / dct_sad / quant_psnr / rd / bit
89 specific compare functions used in encoding, it depends upon the command line
90 switches which of these are used
91 dont waste ur time with dct_sad & quant_psnr they arent really usefull
93 put_pixels_clamped / add_pixels_clamped
94 used for en/decoding in the IDCT, easy
95 Note, some optimized IDCTs have the add/put clamped code included and then
96 put_pixels_clamped / add_pixels_clamped will be unused
99 idct (encoding & decoding)
101 difficult to optimize
104 used for encoding with trellis quantization
105 difficult to optimize
111 used in mpeg1 en/decoding
114 used in mpeg2 en/decoding
117 used in mpeg4/h263 en/decoding
119 FIXME remaining functions?
120 btw, most of these are in dsputil.c/.h some are in mpegvideo.c/.h
125 some instructions on some architectures have strict alignment restrictions,
126 for example most SSE/SSE2 inctructios on X86
127 the minimum guranteed alignment is writen in the .h files
129 void (*put_pixels_clamped)(const DCTELEM *block/*align 16*/, UINT8 *pixels/*align 8*/, int line_size);
134 http://www.aggregate.org/MAGIC/
137 http://developer.intel.com/design/pentium4/manuals/248966.htm
139 The IA-32 Intel Architecture Software Developer's Manual, Volume 2:
140 Instruction Set Reference
141 http://developer.intel.com/design/pentium4/manuals/245471.htm
143 http://www.agner.org/assem/
145 AMD Athlon Processor x86 Code Optimization Guide:
146 http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/22007.pdf
149 official doc but quite ugly
150 http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html
152 a bit old (note "+" is valid for input-output, even though the next says its not)
153 http://www.cs.virginia.edu/~clc5q/gcc-inline-asm.pdf