const

[ffmpeg] / doc / optimization.txt

diff --git a/doc/optimization.txt b/doc/optimization.txt
index 61dc5c40a69fa42a7913ab6841aa4cc11a062b91..27fcbba02fc6dcc911fc6e3802af925af801c894 100644 (file)
--- a/doc/optimization.txt
+++ b/doc/optimization.txt
@@ -1,6 +1,8 @@
 optimization Tips (for libavcodec):
+===================================
 
 What to optimize:
+-----------------
 If you plan to do non-x86 architecture specific optimizations (SIMD normally),
 then take a look in the i386/ directory, as most important functions are
 already optimized for MMX.
@@ -9,7 +11,9 @@ If you want to do x86 optimizations then you can either try to finetune the
 stuff in the i386 directory or find some other functions in the C source to
 optimize, but there aren't many left.
 
+
 Understanding these overoptimized functions:
+--------------------------------------------
 As many functions tend to be a bit difficult to understand because
 of optimizations, it can be hard to optimize them further, or write
 architecture-specific versions. It is recommened to look at older
@@ -23,18 +27,22 @@ and how they can be optimized.
 NOTE: If you still don't understand some function, ask at our mailing list!!!
 (http://lists.mplayerhq.hu/mailman/listinfo/ffmpeg-devel)
 
-What speedup justifies an optimizetion?
-Normaly with clean&simple optimizations and widely used codecs a overall
-speedup of the affected codec of 0.1% is enough. These speedups accumulate
-and can make a big difference after a while ...
-Also if none of the following gets worse and at least one gets better then an
-optimization is always a good idea even if the overall gain is less than 0.1%
-(speed, binary code size, source size, source readability)
-For obscure codecs noone uses, the goal is more toward keeping the code clean
-small and readable than to make it 1% faster.
+
+When is an optimization justified?
+----------------------------------
+Normally, clean and simple optimizations for widely used codecs are
+justified even if they only achieve an overall speedup of 0.1%. These
+speedups accumulate and can make a big difference after awhile. Also, if
+none of the following factors get worse due to an optimization -- speed,
+binary code size, source size, source readability -- and at least one
+factor improves, then an optimization is always a good idea even if the
+overall gain is less than 0.1%. For obscure codecs that are not often
+used, the goal is more toward keeping the code clean, small, and
+readable instead of making it 1% faster.
 
 
 WTF is that function good for ....:
+-----------------------------------
 The primary purpose of that list is to avoid wasting time to optimize functions
 which are rarely used
 
@@ -145,9 +153,11 @@ The minimum guaranteed alignment is written in the .h files, for example:
 
 
 Links:
+======
 http://www.aggregate.org/MAGIC/
 
 x86-specific:
+-------------
 http://developer.intel.com/design/pentium4/manuals/248966.htm
 
 The IA-32 Intel Architecture Software Developer's Manual, Volume 2:
@@ -161,7 +171,7 @@ http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/22007.pd
 
 
 ARM-specific:
-
+-------------
 ARM Architecture Reference Manual (up to ARMv5TE):
 http://www.arm.com/community/university/eulaarmarm.html
 
@@ -176,7 +186,7 @@ Optimization guide for Intel XScale (used in Sharp Zaurus PDA):
 http://download.intel.com/design/intelxscale/27347302.pdf
 
 PowerPC-specific:
-
+-----------------
 PowerPC32/AltiVec PIM:
 www.freescale.com/files/32bit/doc/ref_manual/ALTIVECPEM.pdf
 
@@ -188,6 +198,7 @@ http://www-01.ibm.com/chips/techlib/techlib.nsf/techdocs/30B3520C93F437AB8725706
 http://www-01.ibm.com/chips/techlib/techlib.nsf/techdocs/9F820A5FFA3ECE8C8725716A0062585F/$file/CBE_Handbook_v1.1_24APR2007_pub.pdf
 
 SPARC-specific:
+---------------
 SPARC Joint Programming Specification (JPS1): Commonality
 http://www.fujitsu.com/downloads/PRMPWR/JPS1-R1.0.4-Common-pub.pdf
 
@@ -198,6 +209,7 @@ VIS Whitepaper (contains optimization guidelines)
 http://www.sun.com/processors/vis/download/vis/vis_whitepaper.pdf
 
 GCC asm links:
+--------------
 official doc but quite ugly
 http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html