X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=doc%2Foptimization.txt;h=a14116483d50226f6996be67c13d192b25c188d4;hb=1a592ecc476ec58be430636f1ad07a7dd86089e1;hp=f6033402bb2261f2ce2baba9f814131b71d21429;hpb=5e123bd359226afe7123540e6438a72306c75a2e;p=ffmpeg

diff --git a/doc/optimization.txt b/doc/optimization.txt
index f6033402bb2..a14116483d5 100644
--- a/doc/optimization.txt
+++ b/doc/optimization.txt
@@ -16,7 +16,7 @@ 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
+architecture-specific versions. It is recommended to look at older
 revisions of the interesting files (for a web frontend try ViewVC at
 http://svn.mplayerhq.hu/ffmpeg/trunk/).
 Alternatively, look into the other architecture-specific versions in
@@ -28,22 +28,23 @@ 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
+The primary purpose of this list is to avoid wasting time optimizing functions
+which are rarely used.
 
 put(_no_rnd)_pixels{,_x2,_y2,_xy2}
     Used in motion compensation (en/decoding).
@@ -150,6 +151,22 @@ The minimum guaranteed alignment is written in the .h files, for example:
     void (*put_pixels_clamped)(const DCTELEM *block/*align 16*/, UINT8 *pixels/*align 8*/, int line_size);
 
 
+General Tips:
+-------------
+Use asm loops like:
+asm(
+    "1: ....
+    ...
+    "jump_instruciton ....
+Do not use C loops:
+do{
+    asm(
+        ...
+}while()
+
+Use asm() instead of intrinsics. The latter requires a good optimizing compiler
+which gcc is not.
+
 
 Links:
 ======
@@ -183,6 +200,8 @@ Optimization guide for ARM11 (used in Nokia N800 Internet Tablet):
 http://infocenter.arm.com/help/topic/com.arm.doc.ddi0211j/DDI0211J_arm1136_r1p5_trm.pdf
 Optimization guide for Intel XScale (used in Sharp Zaurus PDA):
 http://download.intel.com/design/intelxscale/27347302.pdf
+Intel Wireless MMX2 Coprocessor: Programmers Reference Manual
+http://download.intel.com/design/intelxscale/31451001.pdf
 
 PowerPC-specific:
 -----------------