frsh: Export information about the last RTP contract and VRES

[frescor/ffmpeg.git] / doc / optimization.txt

diff --git a/doc/optimization.txt b/doc/optimization.txt
index f5a86a3eeeb2009f2b3bfa73667afff83b550777..5469adc8363b2abc2beabfbfcc747ba43cbda67a 100644 (file)
--- a/doc/optimization.txt
+++ b/doc/optimization.txt
@@ -4,11 +4,11 @@ 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
+then take a look in the x86/ directory, as most important functions are
 already optimized for MMX.
 
 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
+stuff in the x86 directory or find some other functions in the C source to
 optimize, but there aren't many left.
 
 
@@ -16,11 +16,11 @@ 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/).
+http://svn.ffmpeg.org/ffmpeg/trunk/).
 Alternatively, look into the other architecture-specific versions in
-the i386/, ppc/, alpha/ subdirectories. Even if you don't exactly
+the x86/, ppc/, alpha/ subdirectories. Even if you don't exactly
 comprehend the instructions, it could help understanding the functions
 and how they can be optimized.
 
@@ -30,21 +30,21 @@ NOTE: If you still don't understand some function, ask at our mailing list!!!
 
 When is an optimization justified?
 ----------------------------------
-Normally, clean & simple optimizations on widely used codecs can 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 than to make it 1%
-faster.
+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).
@@ -151,6 +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:
 ======
@@ -184,6 +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:
 -----------------