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• Difficulty getting Saxon into XQuery mode instead of XSLT

  - by Rosarch

  I'm having difficulty getting XQuery to work. I downloaded Saxon-HE 9.2. It seems to only want to work with XSLT. When I type: java -jar saxon9he.jar I get back usage information for XSLT. When I use the command syntax for XQuery, it doesn't recognize the parameters (like -q), and gives XSLT usage information. Here are some command line interactions: >java -jar saxon9he.jar No source file name Saxon-HE 9.2.0.6J from Saxonica Usage: see http://www.saxonica.com/documentation/using-xsl/commandline.html Options: -a Use xml-stylesheet PI, not -xsl argument -c:filename Use compiled stylesheet from file -config:filename Use configuration file -cr:classname Use collection URI resolver class -dtd:on|off Validate using DTD -expand:on|off Expand defaults defined in schema/DTD -explain[:filename] Display compiled expression tree -ext:on|off Allow|Disallow external Java functions -im:modename Initial mode -ief:class;class;... List of integrated extension functions -it:template Initial template -l:on|off Line numbering for source document -m:classname Use message receiver class -now:dateTime Set currentDateTime -o:filename Output file or directory -opt:0..10 Set optimization level (0=none, 10=max) -or:classname Use OutputURIResolver class -outval:recover|fatal Handling of validation errors on result document -p:on|off Recognize URI query parameters -r:classname Use URIResolver class -repeat:N Repeat N times for performance measurement -s:filename Initial source document -sa Use schema-aware processing -strip:all|none|ignorable Strip whitespace text nodes -t Display version and timing information -T[:classname] Use TraceListener class -TJ Trace calls to external Java functions -tree:tiny|linked Select tree model -traceout:file|#null Destination for fn:trace() output -u Names are URLs not filenames -val:strict|lax Validate using schema -versionmsg:on|off Warn when using XSLT 1.0 stylesheet -warnings:silent|recover|fatal Handling of recoverable errors -x:classname Use specified SAX parser for source file -xi:on|off Expand XInclude on all documents -xmlversion:1.0|1.1 Version of XML to be handled -xsd:file;file.. Additional schema documents to be loaded -xsdversion:1.0|1.1 Version of XML Schema to be used -xsiloc:on|off Take note of xsi:schemaLocation -xsl:filename Stylesheet file -y:classname Use specified SAX parser for stylesheet --feature:value Set configuration feature (see FeatureKeys) -? Display this message param=value Set stylesheet string parameter +param=filename Set stylesheet document parameter ?param=expression Set stylesheet parameter using XPath !option=value Set serialization option >java -jar saxon9he.jar -q:"..\w3xQueryTut.xq" Unknown option -q:..\w3xQueryTut.xq Saxon-HE 9.2.0.6J from Saxonica Usage: see http://www.saxonica.com/documentation/using-xsl/commandline.html Options: -a Use xml-stylesheet PI, not -xsl argument // etc... >java net.sf.saxon.Query -q:"..\w3xQueryTut.xq" Exception in thread "main" java.lang.NoClassDefFoundError: net/sf/saxon/Query Caused by: java.lang.ClassNotFoundException: net.sf.saxon.Query // etc... Could not find the main class: net.sf.saxon.Query. Program will exit. I'm probably making some stupid mistake. Do you know what it could be?

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• int, short, byte performance in back-to-back for-loops

  - by runrunraygun

  (background: http://stackoverflow.com/questions/1097467/why-should-i-use-int-instead-of-a-byte-or-short-in-c) To satisfy my own curiosity about the pros and cons of using the "appropriate size" integer vs the "optimized" integer i wrote the following code which reinforced what I previously held true about int performance in .Net (and which is explained in the link above) which is that it is optimized for int performance rather than short or byte. DateTime t; long a, b, c; t = DateTime.Now; for (int index = 0; index < 127; index++) { Console.WriteLine(index.ToString()); } a = DateTime.Now.Ticks - t.Ticks; t = DateTime.Now; for (short index = 0; index < 127; index++) { Console.WriteLine(index.ToString()); } b=DateTime.Now.Ticks - t.Ticks; t = DateTime.Now; for (byte index = 0; index < 127; index++) { Console.WriteLine(index.ToString()); } c=DateTime.Now.Ticks - t.Ticks; Console.WriteLine(a.ToString()); Console.WriteLine(b.ToString()); Console.WriteLine(c.ToString()); This gives roughly consistent results in the area of... ~950000 ~2000000 ~1700000 which is in line with what i would expect to see. However when I try repeating the loops for each data type like this... t = DateTime.Now; for (int index = 0; index < 127; index++) { Console.WriteLine(index.ToString()); } for (int index = 0; index < 127; index++) { Console.WriteLine(index.ToString()); } for (int index = 0; index < 127; index++) { Console.WriteLine(index.ToString()); } a = DateTime.Now.Ticks - t.Ticks; the numbers are more like... ~4500000 ~3100000 ~300000 Which I find puzzling. Can anyone offer an explanation? NOTE: In the interest of compairing like for like i've limited the loops to 127 because of the range of the byte value type. Also this is an act of curiosity not production code micro-optimization.

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• compile AMR-nb codec with RVCT for WinCE/Window Mobile

  - by pps

  Hello everybody, I'm working on amr speech codec (porting/optimization) I have an arm (for WinCE) optimized version from voiceage and I use it as a reference in performance testing. So far, binary produced with my lib beats the other one by around 20-30%! I use Vs2008 and I have limited access to ARM instruction set I can generate with Microsoft compiler. So I tried to look for alternative compiler to see what would be performance difference. I have RVCT compiler, but it produces elf binaries/object files. However, I run my test on a wince mobile phone (TyTn 2) so I need to find a way to run code compiled with RVCT on WinCE. Some of the options are 1) to produce assembly listing (-S option of armcc), and try to assemble with some other assembler that can create COFF (MS assembler for arm) 2) compile and convert generated ELF object file to COFF object (seems like objcopy of gnu binutils could help me with that) 3) using fromelf utility supplied by RVCT create BIN file and somehow try to mangle the bits so I can execute them ;) My first attempt is to create a simple c++ file with one exported function, compile it with RVCT and then try to run that function on the smartphone. The emitted assembly cannot be assembled by the ms assembler (not only they are not compatible, but also ms assembler rejects some of the instructions generated with RVCT compiler; ASR opcode in my case) Then I tried to convert ELF object to coff format and I can't find any information on that. There is a gcc port for ce and objcopy from that toolset is supposed to be able to do the task. However, I can't get it working. I tried different switches, but I have no idea what exactly I need to specify as bfdname for input and output format. So, I couldn't get it working either. Dumping with fromelf and using generated bin file seems to be overkill, so I decided to ask you guys if there is anything I should try to do or maybe someone has already done similar task and could help me. Basically, all I want to do is to compile my code with RVCT compiler and see what's the performance difference. My code has zero dependencies on any c runtime functions. thanks!

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• Loading .png image from array of uint8_t into OpenGL ES texture

  - by unknownthreat

  Normally, when we want to load a texture for OpenGL ES with .png, we simply add the .png images into XCode. The .png files will be altered for optimization by XCode and these altered png files can loaded into OpenGL ES texture during the runtime. However, what I am trying to do is quite different. I am trying to load a .png file that is not from the prebuilt/compile. The png file will be transmitted externally from UDP, and it will be in the form of array of bytes. I am very sure that the png is transferred correctly, but when it comes to displaying the png image in the form of the OpenGL ES texture, the image somehow shows incorrectly. The colors that are being sent are presented but the positions are somehow very incorrect. However, the position of the colors still retain some aspects of the original position. Here: The left image shows the original .png, while the right shows the png being displayed on iPhone using OpenGL ES Texture. It looks more like the png data is not being decoded or incorrectly processed. Below is OpenGL ES code for turning the image into texture: - (void) setTextureFromImageByte: (uint8_t*)imageByte{ if (self = [super init]){ NSData* imageData = [[NSData alloc] initWithBytes: imageByte length: imageLength]; UIImage* img = [[UIImage alloc] initWithData: imageData]; CGImageRef image = img.CGImage; int width = 512; int height = 512; if (image){ int tempWidth = (int)width, tempHeight = (int)height; if ((tempWidth & (tempWidth - 1)) != 0 ){ NSLog(@"CAUTION! width is not power of 2. width == %d", tempWidth); }else if ((tempHeight & (tempHeight - 1)) != 0 ){ NSLog(@"CAUTION! height is not power of 2. height == %d", tempHeight); }else{ void *spriteData = calloc(width * 4, height * 4); CGContextRef spriteContext = CGBitmapContextCreate(spriteData, width, height, 8, width*4, CGImageGetColorSpace(image), kCGImageAlphaPremultipliedLast); CGContextDrawImage(spriteContext, CGRectMake(0.0, 0.0, width, height), image); CGContextRelease(spriteContext); glBindTexture(GL_TEXTURE_2D, 1); glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 320, 435, GL_RGBA, GL_UNSIGNED_BYTE, spriteData); free(spriteData); } }else NSLog(@"ERROR: Image not loaded..."); [img release]; [imageData release]; } } So does anyone knows how to deal with this? Is it because of iPhone only accepts altered png from XCode? What can we do in this case in order to make the png image be able to display correctly?

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• GCC, -O2, and bitfields - is this a bug or a feature?

  - by Rooke

  Today I discovered alarming behavior when experimenting with bit fields. For the sake of discussion and simplicity, here's an example program: #include <stdio.h> struct Node { int a:16 __attribute__ ((packed)); int b:16 __attribute__ ((packed)); unsigned int c:27 __attribute__ ((packed)); unsigned int d:3 __attribute__ ((packed)); unsigned int e:2 __attribute__ ((packed)); }; int main (int argc, char *argv[]) { Node n; n.a = 12345; n.b = -23456; n.c = 0x7ffffff; n.d = 0x7; n.e = 0x3; printf("3-bit field cast to int: %d\n",(int)n.d); n.d++; printf("3-bit field cast to int: %d\n",(int)n.d); } The program is purposely causing the 3-bit bit-field to overflow. Here's the (correct) output when compiled using "g++ -O0": 3-bit field cast to int: 7 3-bit field cast to int: 0 Here's the output when compiled using "g++ -O2" (and -O3): 3-bit field cast to int: 7 3-bit field cast to int: 8 Checking the assembly of the latter example, I found this: movl $7, %esi movl $.LC1, %edi xorl %eax, %eax call printf movl $8, %esi movl $.LC1, %edi xorl %eax, %eax call printf xorl %eax, %eax addq $8, %rsp The optimizations have just inserted "8", assuming 7+1=8 when in fact the number overflows and is zero. Fortunately the code I care about doesn't overflow as far as I know, but this situation scares me - is this a known bug, a feature, or is this expected behavior? When can I expect gcc to be right about this? Edit (re: signed/unsigned) : It's being treated as unsigned because it's declared as unsigned. Declaring it as int you get the output (with O0): 3-bit field cast to int: -1 3-bit field cast to int: 0 An even funnier thing happens with -O2 in this case: 3-bit field cast to int: 7 3-bit field cast to int: 8 I admit that attribute is a fishy thing to use; in this case it's a difference in optimization settings I'm concerned about.

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• Understanding CLR 2.0 Memory Model

  - by Eloff

  Joe Duffy, gives 6 rules that describe the CLR 2.0+ memory model (it's actual implementation, not any ECMA standard) I'm writing down my attempt at figuring this out, mostly as a way of rubber ducking, but if I make a mistake in my logic, at least someone here will be able to catch it before it causes me grief. Rule 1: Data dependence among loads and stores is never violated. Rule 2: All stores have release semantics, i.e. no load or store may move after one. Rule 3: All volatile loads are acquire, i.e. no load or store may move before one. Rule 4: No loads and stores may ever cross a full-barrier (e.g. Thread.MemoryBarrier, lock acquire, Interlocked.Exchange, Interlocked.CompareExchange, etc.). Rule 5: Loads and stores to the heap may never be introduced. Rule 6: Loads and stores may only be deleted when coalescing adjacent loads and stores from/to the same location. I'm attempting to understand these rules. x = y y = 0 // Cannot move before the previous line according to Rule 1. x = y z = 0 // equates to this sequence of loads and stores before possible re-ordering load y store x load 0 store z Looking at this, it appears that the load 0 can be moved up to before load y, but the stores may not be re-ordered at all. Therefore, if a thread sees z == 0, then it also will see x == y. If y was volatile, then load 0 could not move before load y, otherwise it may. Volatile stores don't seem to have any special properties, no stores can be re-ordered with respect to each other (which is a very strong guarantee!) Full barriers are like a line in the sand which loads and stores can not be moved over. No idea what rule 5 means. I guess rule 6 means if you do: x = y x = z Then it is possible for the CLR to delete both the load to y and the first store to x. x = y z = y // equates to this sequence of loads and stores before possible re-ordering load y store x load y store z // could be re-ordered like this load y load y store x store z // rule 6 applied means this is possible? load y store x // but don't pop y from stack (or first duplicate item on top of stack) store z What if y was volatile? I don't see anything in the rules that prohibits the above optimization from being carried out. This does not violate double-checked locking, because the lock() between the two identical conditions prevents the loads from being moved into adjacent positions, and according to rule 6, that's the only time they can be eliminated. So I think I understand all but rule 5, here. Anyone want to enlighten me (or correct me or add something to any of the above?)

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• gcc/g++: error when compiling large file

  - by Alexander

  Hi, I have a auto-generated C++ source file, around 40 MB in size. It largely consists of push_back commands for some vectors and string constants that shall be pushed. When I try to compile this file, g++ exits and says that it couldn't reserve enough virtual memory (around 3 GB). Googling this problem, I found that using the command line switches --param ggc-min-expand=0 --param ggc-min-heapsize=4096 may solve the problem. They, however, only seem to work when optimization is turned on. 1) Is this really the solution that I am looking for? 2) Or is there a faster, better (compiling takes ages with these options acitvated) way to do this? Best wishes, Alexander Update: Thanks for all the good ideas. I tried most of them. Using an array instead of several push_back() operations reduced memory usage, but as the file that I was trying to compile was so big, it still crashed, only later. In a way, this behaviour is really interesting, as there is not much to optimize in such a setting -- what does the GCC do behind the scenes that costs so much memory? (I compiled with deactivating all optimizations as well and got the same results) The solution that I switched to now is reading in the original data from a binary object file that I created from the original file using objcopy. This is what I originally did not want to do, because creating the data structures in a higher-level language (in this case Perl) was more convenient than having to do this in C++. However, getting this running under Win32 was more complicated than expected. objcopy seems to generate files in the ELF format, and it seems that some of the problems I had disappeared when I manually set the output format to pe-i386. The symbols in the object file are by standard named after the file name, e.g. converting the file inbuilt_training_data.bin would result in these two symbols: binary_inbuilt_training_data_bin_start and binary_inbuilt_training_data_bin_end. I found some tutorials on the web which claim that these symbols should be declared as extern char _binary_inbuilt_training_data_bin_start;, but this does not seem to be right -- only extern char binary_inbuilt_training_data_bin_start; worked for me.

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• Getting <divs>'s to align next to each other

  - by user1322845

  I have the following code I am trying to get working correctly: <div id="newspost_bg"> <article> <p> <header><h3>The fast red fox!</h3></header> This is where the article resides in the article tag. This is good for SEO optimization. <footer>Read More..</footer> </p> </article> </div> <div id="newspost_bg"> hello </div> <div id="newspost_bg"> hello </div> <div id="advertisement"> <script type="text/javascript"><!-- google_ad_client = "ca-pub-2139701283631933"; /* testing site */ google_ad_slot = "4831288817"; google_ad_width = 120; google_ad_height = 600; //--> </script> </div> Here is the css that goes with it: #newspost_bg{ position: relative; background-color: #d9dde1; width:700px; height:250px; margin: 10px; margin-left: 20px; border: solid 10px #1d2631; float:left; } #newspost_bg article{ position: relative; margin-left: 20px; } #advertisement{ float: left; background-color: #d9dde1; width: 125px; height: 605px; margin: 10px; } The problem I'm experiencing is that the advertisements im trying to get setup will align with the last with the id of newspost_bg but im looking to havce it align to the top of the container it is in. I dont know if this is enough info, if not please let me know what you might need. Im new to the web coding scene so any and all critiques help me.

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• If Then Statement Condition Being Ignored With Optimisations On

  - by Matma

  I think im going mad but can some show me what im missing, it must be some stupidly simple i just cant see the wood for the trees. BOTH side of this if then else statement are being executed? Ive tried commenting out the true side and moving the condition to a seperate variable with the same result. However if i explicitly set the condition to 1=0 or 1=1 then the if then statement is operating as i would expect. i.e. only executing one side of the equation... The only time ive seen this sort of thing is when the compiler has crashed and is no longer compiling (without visible indication that its not) but ive restarted studio with the same results, ive cleaned the solution, built and rebuilt with no change? please show me the stupid mistake im making using vs2005 if it matters. Dim dset As DataSet = New DataSet If (CboCustomers.SelectedValue IsNot Nothing) AndAlso (CboCustomers.SelectedValue <> "") Then Dim Sql As String = "Select sal.SalesOrderNo As SalesOrder,cus.CustomerName,has.SerialNo, convert(varchar,sal.Dateofpurchase,103) as Date from [dbo].[Customer_Table] as cus " & _ " inner join [dbo].[Hasp_table] as has on has.CustomerID=cus.CustomerTag " & _ " inner join [dbo].[salesorder_table] as sal On sal.Hasp_ID =has.Hasp_ID Where cus.CustomerTag = '" & CboCustomers.SelectedValue.ToString & "'" Dim dap As SqlDataAdapter = New SqlDataAdapter(Sql, FormConnection) dap.Fill(dset, "dbo.Customer_Table") DGCustomer.DataSource = dset.Tables("dbo.Customer_Table") Else Dim erm As String = "wtf" End If EDIT: i have found that this is something to do with the release config settings im using, i guesing its the optimisations bit. does anyone know of any utils/addons for vs that show if a line has been optimised out. delphi, my former language showed blue dots in the left margin to show that it was a compiled line, no dot meaning it wasnt compiled in, is there anything like that for vs? alternatively can someone explain how optimisations would affect this simple if statement causeing it to run both sides? EDIT2: using this thread as possible causes/solutions : http://stackoverflow.com/questions/2135509/bug-only-occurring-when-compile-optimization-enabled. It does the same with release = optimisations on, x86, x64 and AnyCPU Goes away with optimisations off. Im using V2005 on a x64 win7 machine, if that matters. Thanks

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• Help with C# program design implementation: multiple array of lists or a better way?

  - by Bob

  I'm creating a 2D tile-based RPG in XNA and am in the initial design phase. I was thinking of how I want my tile engine to work and came up with a rough sketch. Basically I want a grid of tiles, but at each tile location I want to be able to add more than one tile and have an offset. I'd like this so that I could do something like add individual trees on the world map to give more flair. Or set bottles on a bar in some town without having to draw a bunch of different bar tiles with varying bottles. But maybe my reach is greater than my grasp. I went to implement the idea and had something like this in my Map object: List<Tile>[,] Grid; But then I thought about it. Let's say I had a world map of 200x200, which would actually be pretty small as far as RPGs go. That would amount to 40,000 Lists. To my mind I think there has to be a better way. Now this IS pre-mature optimization. I don't know if the way I happen to design my maps and game will be able to handle this, but it seems needlessly inefficient and something that could creep up if my game gets more complex. One idea I have is to make the offset and the multiple tiles optional so that I'm only paying for them when needed. But I'm not sure how I'd do this. A multiple array of objects? object[,] Grid; So here's my criteria: A 2D grid of tile locations Each tile location has a minimum of 1 tile, but can optionally have more Each extra tile can optionally have an x and y offset for pinpoint placement Can anyone help with some ideas for implementing such a design (don't need it done for me, just ideas) while keeping memory usage to a minimum? If you need more background here's roughly what my Map and Tile objects amount to: public struct Map { public Texture2D Texture; public List<Rectangle> Sources; //Source Rectangles for where in Texture to get the sprite public List<Tile>[,] Grid; } public struct Tile { public int Index; //Where in Sources to find the source Rectangle public int X, Y; //Optional offsets }

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• CMake: Mac OS X: ld: unknown option: -soname

  - by Alex Ivasyuv

  I try to build my app with CMake on Mac OS X, I get the following error: Linking CXX shared library libsml.so ld: unknown option: -soname collect2: ld returned 1 exit status make[2]: *** [libsml.so] Error 1 make[1]: *** [CMakeFiles/sml.dir/all] Error 2 make: *** [all] Error 2 This is strange, as Mac has .dylib extension instead of .so. There's my CMakeLists.txt: cmake_minimum_required(VERSION 2.6) PROJECT (SilentMedia) SET(SourcePath src/libsml) IF (DEFINED OSS) SET(OSS_src ${SourcePath}/Media/Audio/SoundSystem/OSS/DSP/DSP.cpp ${SourcePath}/Media/Audio/SoundSystem/OSS/Mixer/Mixer.cpp ) ENDIF(DEFINED OSS) IF (DEFINED ALSA) SET(ALSA_src ${SourcePath}/Media/Audio/SoundSystem/ALSA/DSP/DSP.cpp ${SourcePath}/Media/Audio/SoundSystem/ALSA/Mixer/Mixer.cpp ) ENDIF(DEFINED ALSA) SET(SilentMedia_src ${SourcePath}/Utils/Base64/Base64.cpp ${SourcePath}/Utils/String/String.cpp ${SourcePath}/Utils/Random/Random.cpp ${SourcePath}/Media/Container/FileLoader.cpp ${SourcePath}/Media/Container/OGG/OGG.cpp ${SourcePath}/Media/PlayList/XSPF/XSPF.cpp ${SourcePath}/Media/PlayList/XSPF/libXSPF.cpp ${SourcePath}/Media/PlayList/PlayList.cpp ${OSS_src} ${ALSA_src} ${SourcePath}/Media/Audio/Audio.cpp ${SourcePath}/Media/Audio/AudioInfo.cpp ${SourcePath}/Media/Audio/AudioProxy.cpp ${SourcePath}/Media/Audio/SoundSystem/SoundSystem.cpp ${SourcePath}/Media/Audio/SoundSystem/libao/AO.cpp ${SourcePath}/Media/Audio/Codec/WAV/WAV.cpp ${SourcePath}/Media/Audio/Codec/Vorbis/Vorbis.cpp ${SourcePath}/Media/Audio/Codec/WavPack/WavPack.cpp ${SourcePath}/Media/Audio/Codec/FLAC/FLAC.cpp ) SET(SilentMedia_LINKED_LIBRARY sml vorbisfile FLAC++ wavpack ao #asound boost_thread-mt boost_filesystem-mt xspf gtest ) INCLUDE_DIRECTORIES( /usr/include /usr/local/include /usr/include/c++/4.4 /Users/alex/Downloads/boost_1_45_0 ${SilentMedia_SOURCE_DIR}/src ${SilentMedia_SOURCE_DIR}/${SourcePath} ) #link_directories( # /usr/lib # /usr/local/lib # /Users/alex/Downloads/boost_1_45_0/stage/lib #) IF(LibraryType STREQUAL "static") ADD_LIBRARY(sml-static STATIC ${SilentMedia_src}) # rename library from libsml-static.a => libsml.a SET_TARGET_PROPERTIES(sml-static PROPERTIES OUTPUT_NAME "sml") SET_TARGET_PROPERTIES(sml-static PROPERTIES CLEAN_DIRECT_OUTPUT 1) ELSEIF(LibraryType STREQUAL "shared") ADD_LIBRARY(sml SHARED ${SilentMedia_src}) # change compile optimization/debug flags # -Werror -pedantic IF(BuildType STREQUAL "Debug") SET_TARGET_PROPERTIES(sml PROPERTIES COMPILE_FLAGS "-pipe -Wall -W -ggdb") ELSEIF(BuildType STREQUAL "Release") SET_TARGET_PROPERTIES(sml PROPERTIES COMPILE_FLAGS "-pipe -Wall -W -O3 -fomit-frame-pointer") ENDIF() SET_TARGET_PROPERTIES(sml PROPERTIES CLEAN_DIRECT_OUTPUT 1) ENDIF() ### TEST ### IF(Test STREQUAL "true") ADD_EXECUTABLE (bin/TestXSPF ${SourcePath}/Test/Media/PlayLists/XSPF/TestXSPF.cpp) TARGET_LINK_LIBRARIES (bin/TestXSPF ${SilentMedia_LINKED_LIBRARY}) ADD_EXECUTABLE (bin/test1 ${SourcePath}/Test/test.cpp) TARGET_LINK_LIBRARIES (bin/test1 ${SilentMedia_LINKED_LIBRARY}) ADD_EXECUTABLE (bin/TestFileLoader ${SourcePath}/Test/Media/Container/FileLoader/TestFileLoader.cpp) TARGET_LINK_LIBRARIES (bin/TestFileLoader ${SilentMedia_LINKED_LIBRARY}) ADD_EXECUTABLE (bin/testMixer ${SourcePath}/Test/testMixer.cpp) TARGET_LINK_LIBRARIES (bin/testMixer ${SilentMedia_LINKED_LIBRARY}) ENDIF (Test STREQUAL "true") ### TEST ### ADD_CUSTOM_TARGET(doc COMMAND doxygen ${SilentMedia_SOURCE_DIR}/doc/Doxyfile) There was no error on Linux. Build process: cmake -D BuildType=Debug -D LibraryType=shared . make I found, that incorrect command generate in CMakeFiles/sml.dir/link.txt. But why, as the goal of CMake is cross-platforming.. How to fix it?

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• Improving performance on data pasting 2000 rows with validations

  - by Lohit

  I have N rows (which could be nothing less than 1000) on an excel spreadsheet. And in this sheet our project has 150 columns like this: Now, our application needs data to be copied (using normal Ctrl+C) and pasted (using Ctrl+V) from the excel file sheet on our GUI sheet. Copy pasting 1000 records takes around 5-6 seconds which is okay for our requirement, but the problem is when we need to make sure the data entered is valid. So we have to validate data in each row generate appropriate error messages and format the data as per requirement. So we need to at runtime parse and evaluate data in each row. Now all the formatting of data and validations come from the back-end database and we have it in a data-table (dtValidateAndFormatConditions). The conditions would be around 50. So you can see how slow this whole process becomes since N X 150 X 50 operations are required to complete this whole process. Initially it took approximately 2-3 minutes but now i have reduced it to 20 - 30 seconds. However i have increased the speed by making an expression parser of my own - and not by any algorithm, is there any other way i can improve performance, by using Divide and Conquer or some other mechanism. Currently i am not really sure how to go about this. Here is what part of my code looks like: public virtual void ValidateAndFormatOnCopyPaste(DataTable DtCopied, int CurRow) { foreach (DataRow dRow in dtValidateAndFormatConditions.Rows) { string Condition = dRow["Condition"]; string FormatValue = Value = dRow["Value"]; GetValidatedFormattedData(DtCopied,ref Condition, ref FormatValue ,iRowIndex); Condition = Parse(Condition); dRow["Condition"] = Condition; FormatValue = Parse(FormatValue ); dRow["Value"] = FormatValue; } } The above code gets called row-wise like this: public override void ValidateAndFormat(DataTable dtChangedRecords, CellRange cr) { int iRowStart = cr.Row, iRowEnd = cr.Row + cr.RowCount; for (int iRow = iRowStart; iRow < iRowEnd; iRow++) { ValidateAndFormatOnCopyPaste(dtChangedRecords,iRow); } } Please know my question needs a more algorithmic solution than code optimization, however any answers containing code related optimizations will be appreciated as well. (Tagged Linq because although not seen i have been using linq in some parts of my code).

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• Scalable Database Tagging Schema

  - by Longpoke

  EDIT: To people building tagging systems. Don't read this. It is not what you are looking for. I asked this when I wasn't aware that RDBMS all have their own optimization methods, just use a simple many to many scheme. I have a posting system that has millions of posts. Each post can have an infinite number of tags associated with it. Users can create tags which have notes, date created, owner, etc. A tag is almost like a post itself, because people can post notes about the tag. Each tag association has an owner and date, so we can see who added the tag and when. My question is how can I implement this? It has to be fast searching posts by tag, or tags by post. Also, users can add tags to posts by typing the name into a field, kind of like the google search bar, it has to fill in the rest of the tag name for you. I have 3 solutions at the moment, but not sure which is the best, or if there is a better way. Note that I'm not showing the layout of notes since it will be trivial once I get a proper solution for tags. Method 1. Linked list tagId in post points to a linked list in tag_assoc, the application must traverse the list until flink=0 post: id, content, ownerId, date, tagId, notesId tag_assoc: id, tagId, ownerId, flink tag: id, name, notesId Method 2. Denormalization tags is simply a VARCHAR or TEXT field containing a tab delimited array of tagId:ownerId. It cannot be a fixed size. post: id, content, ownerId, date, tags, notesId tag: id, name, notesId Method 3. Toxi (from: http://www.pui.ch/phred/archives/2005/04/tags-database-schemas.html, also same thing here: http://stackoverflow.com/questions/20856/how-do-you-recommend-implementing-tags-or-tagging) post: id, content, ownerId, date, notesId tag_assoc: ownerId, tagId, postId tag: id, name, notesId Method 3 raises the question, how fast will it be to iterate through every single row in tag_assoc? Methods 1 and 2 should be fast for returning tags by post, but for posts by tag, another lookup table must be made. The last thing I have to worry about is optimizing searching tags by name, I have not worked that out yet. I made an ASCII diagram here: http://pastebin.com/f1c4e0e53

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• What is fastest way to convert bool to byte?

  - by Amir Rezaei

  What is fastest way to convert bool to byte? I want this mapping: False=0, True=1 Note: I don't want to use any if statement. Update: I don't want to use conditional statement. I don't want the CPU to halt or guess next statement. I want to optimize this code: private static string ByteArrayToHex(byte[] barray) { char[] c = new char[barray.Length * 2]; byte k; for (int i = 0; i < barray.Length; ++i) { k = ((byte)(barray[i] >> 4)); c[i * 2] = (char)(k > 9 ? k + 0x37 : k + 0x30); k = ((byte)(barray[i] & 0xF)); c[i * 2 + 1] = (char)(k > 9 ? k + 0x37 : k + 0x30); } return new string(c); } Update: The length of the array is very large, it's in terabyte order! Therefore I need to do optimization if possible. I shouldn't need to explain my self. The question is still valid. Update: I'm working on a project and looking at others code. That's why I didn't provide with the function at first place. I didn't want to spend time on explaining for people when they have opinion about the code. I shouldn’y need to provide in my question the background of my work, and a function that is not written by me. I have started to optimize it part by part. If I needed help with the whole function I would asked that in another question. That is why I asked this very simple at the beginning. Unfortunately people couldn’t keep themselves to the question. So please if you want to help answer the question. Update: For dose who want to see the point of this question. This example shows how two if statement are reduced from the code. byte A = k > 9 ; //If it was possible (k>9) == 0 || 1 c[i * 2] = A * (k + 0x30) - (A - 1) * (k + 0x30);

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• Thoughts on streamlining multiple .Net apps

  - by John Virgolino

  We have a series of ASP.Net applications that have been written over the course of 8 years. Mostly in the first 3-4 years. They have been running quite well with little maintenance, but new functionality is being requested and we are running into IDE and platform issues. The apps were written in .Net 1.x and 2.x and run in separate spaces but are presented as a single suite of applications which use a common navigation toolbar (implemented as a user control). Every time we want to add something to a menu in the nav we have to modify it in all the apps which is a pain. Also, the various versions of Crystal reports and that we used tables to organize the visual elements and we end up with a mess, especially with all the multi-platform .Net versions running. We need to streamline the suite of apps and make it easier to add on new apps without a hassle. We also need to bring all these apps under one .Net platform and IDE. In addition, there is a WordPress blog styled to match the style of the application suite "integrated" into the UI and a link to a MediaWiki Wiki application as well. My current thinking is to use an open source content management system (CMS) like Joomla (PHP based unfortunately, but it works well) as the user interface framework for style templating and menu management. Joomla's article management would allow us to migrate the Wiki content into articles which could be published without interfering with the .Net apps. Then essentially use an IFrame within an "article" to "host" the .Net application, then... Upgrade the .Net apps to VS2010, strip out all the common header/footer controls and migrate the styles to use the style sheets used in the CMS. As I write this, I certainly realize this is a lot of work and there are optimization issues which this may cause as well as using IFrames seems a bit like cheating and I've read about issues with IFrames. I know that we could use .Net application styling, but it seems like a lot more work (not sure really). Also, the use of a CMS to handle the blog and wiki also seems appealing, unless there is a .Net CMS out there that can handle all of these requirements. Given this information, I am looking to know if I am totally going in the wrong direction? We tried to use open source and integrate it over time, but not this has become hard to maintain. Am I not aware of some technology out there that will meet our requirements? Did we do this right and should we just focus on getting the .Net streamlined? I understand that no matter what we do, it's going to be a lot of work. The communities considerable experience would be helpful. Thanks!! PS - A complete rewrite is not an option.

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• How to properly preload images, js and css files?

  - by Kenny Bones

  Hi, I'm creating a website from scratch and I was really into this in the late 90's but the web has changed alot since then! And I'm more of a designer so when I started putting this site together, I basically did a system of php includes to make the site more "dynamic" When you first visit the site, you'll be presented to a logon screen, if you're not already logged on (cookies). If you're not logged on, a page called access.php is introdused. I thought I'd preload the most heavy images at this point. So that when the user is done logging on, the images are already cached. And this is working as I want. But I still notice that the biggest image still isn't rendered immediatly anyway. So it's seems kinda pointless. All of this has made me rethink how the site is structured and how scripts and css files are loaded. Using FireBug and YSlow with Firefox I see a few pointers like expires headers and reducing the size of each script. But is this really the culprit? For example, would this be really really stupid in the main index.php? The entire site is basically structured like this <?php require("dbconnect.php"); ?> <?php include ("head.php"); ?> And below this is basically just the body and the content of the site. Head.php however consists of the doctype, head portions, linking of two css style sheets, jQuery library, jQuery validation engine, Cufon and Cufon font file, and then the small Cufon.Replace snippet. The rest of the body comes with the index.php file, but at the bottom of this again is an include of a file called "footer.php" which basically consists of loading of a couple of jsLoader scripts and a slidepanel and then a js function. All of this makes the end page source look like a typical complete webpage, but I'm wondering if any of you can see immediatly that "this is really really stupid" and "don't do that, do this instead" etc. :) Are includes a bad way to go? This site is also pretty image intensive and I can probably do a little more optimization. But I don't think that's its the primary culprit. YSlow gives me a report of what takes up the most space: doc(1) - 5.8K js(5) - 198.7K css(2) - 5.6K cssimage(8) - 634.7K image(6) - 110.8K I know it looks like it's cssimage(8) that weighs the most, but I've already preloaded these images from before and it doesn't really affect the rendering.

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• template pass by const reference

  - by 7vies

  Hi, I've looked over a few similar questions, but I'm still confused. I'm trying to figure out how to explicitly (not by compiler optimization etc) and C++03-compatible avoid copying of an object when passing it to a template function. Here is my test code: #include <iostream> using namespace std; struct C { C() { cout << "C()" << endl; } C(const C&) { cout << "C(C)" << endl; } ~C() { cout << "~C()" << endl; } }; template<class T> void f(T) { cout << "f<T>" << endl; } template<> void f(C c) { cout << "f<C>" << endl; } // (1) template<> void f(const C& c) { cout << "f<C&>" << endl; } // (2) int main() { C c; f(c); return 0; } (1) accepts the object of type C, and makes a copy. Here is the output: C() C(C) f<C> ~C() ~C() So I've tried to specialize with a const C& parameter (2) to avoid this, but this simply doesn't work (apparently the reason is explained in this question). Well, I could "pass by pointer", but that's kind of ugly. So is there some trick that would allow to do that somehow nicely? EDIT: Oh, probably I wasn't clear. I already have a templated function template<class T> void f(T) {...} But now I want to specialize this function to accept a const& to another object: template<> void f(const SpecificObject&) {...} But it only gets called if I define it as template<> void f(SpecificObject) {...}

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• thread management in nbody code of cuda-sdk

  - by xnov

  When I read the nbody code in Cuda-SDK, I went through some lines in the code and I found that it is a little bit different than their paper in GPUGems3 "Fast N-Body Simulation with CUDA". My questions are: First, why the blockIdx.x is still involved in loading memory from global to share memory as written in the following code? for (int tile = blockIdx.y; tile < numTiles + blockIdx.y; tile++) { sharedPos[threadIdx.x+blockDim.x*threadIdx.y] = multithreadBodies ? positions[WRAP(blockIdx.x + q * tile + threadIdx.y, gridDim.x) * p + threadIdx.x] : //this line positions[WRAP(blockIdx.x + tile, gridDim.x) * p + threadIdx.x]; //this line __syncthreads(); // This is the "tile_calculation" function from the GPUG3 article. acc = gravitation(bodyPos, acc); __syncthreads(); } isn't it supposed to be like this according to paper? I wonder why sharedPos[threadIdx.x+blockDim.x*threadIdx.y] = multithreadBodies ? positions[WRAP(q * tile + threadIdx.y, gridDim.x) * p + threadIdx.x] : positions[WRAP(tile, gridDim.x) * p + threadIdx.x]; Second, in the multiple threads per body why the threadIdx.x is still involved? Isn't it supposed to be a fix value or not involving at all because the sum only due to threadIdx.y if (multithreadBodies) { SX_SUM(threadIdx.x, threadIdx.y).x = acc.x; //this line SX_SUM(threadIdx.x, threadIdx.y).y = acc.y; //this line SX_SUM(threadIdx.x, threadIdx.y).z = acc.z; //this line __syncthreads(); // Save the result in global memory for the integration step if (threadIdx.y == 0) { for (int i = 1; i < blockDim.y; i++) { acc.x += SX_SUM(threadIdx.x,i).x; //this line acc.y += SX_SUM(threadIdx.x,i).y; //this line acc.z += SX_SUM(threadIdx.x,i).z; //this line } } } Can anyone explain this to me? Is it some kind of optimization for faster code?

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• Refactor a link and an image

  - by Mihail Stoynov

  I have to write an link with an image inside. Instead of explaining, here's the code I have now: <c:if test="${userSession.loggedUser eq null and company.image != null}"> <a onclick="${rich:component('loginPanel')}.show()"> <img src="/download.do?hash=#{company.image.hash}" /> </a> </c:if> <c:if test="${userSession.loggedUser eq null and company.image == null}"> <a onclick="${rich:component('loginPanel')}.show()"> <img src="${request.contextPath}/img/icons/logo_default.jpg" /> </a> </c:if> <c:if test="${userSession.loggedUser ne null and company.image != null}"> <a href="company.xhtml?${company.name}"> <img src="/download.do?hash=#{company.image.hash}" /> </a> </c:if> <c:if test="#{userSession.loggedUser ne null and company.image == null}"> <a href="company.xhtml?${company.name}"> <img src="${request.contextPath}/img/icons/logo_default.jpg" /> </a> </c:if> This code looks awful - there are two exact links with two exact images but combined in all possible combinations. Is there a better way? Is there a way to avoid c:if - it created tables? Update: Bozho proposes: You can replace <c:if and <a with <h:outputLink rendered="#{..}". Apart from that I don't see any other optimization. But it doesn't work. This does not render correctly: <a href=> <h:outputLink rendered="#{..} <h:outputLink rendered="#{..} </a> (the image is outside the anchor) This does render fine: <h:outputLink value=> <h:outputLink rendered="#{..} <h:outputLink rendered="#{..} </a> , but it always adds href and in two of the cases I don't want href when rendered.

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• Akka framework support for finding duplicate messages

  - by scala_is_awesome

  I'm trying to build a high-performance distributed system with Akka and Scala. If a message requesting an expensive (and side-effect-free) computation arrives, and the exact same computation has already been requested before, I want to avoid computing the result again. If the computation requested previously has already completed and the result is available, I can cache it and re-use it. However, the time window in which duplicate computation can be requested may be arbitrarily small. e.g. I could get a thousand or a million messages requesting the same expensive computation at the same instant for all practical purposes. There is a commercial product called Gigaspaces that supposedly handles this situation. However there seems to be no framework support for dealing with duplicate work requests in Akka at the moment. Given that the Akka framework already has access to all the messages being routed through the framework, it seems that a framework solution could make a lot of sense here. Here is what I am proposing for the Akka framework to do: 1. Create a trait to indicate a type of messages (say, "ExpensiveComputation" or something similar) that are to be subject to the following caching approach. 2. Smartly (hashing etc.) identify identical messages received by (the same or different) actors within a user-configurable time window. Other options: select a maximum buffer size of memory to be used for this purpose, subject to (say LRU) replacement etc. Akka can also choose to cache only the results of messages that were expensive to process; the messages that took very little time to process can be re-processed again if needed; no need to waste precious buffer space caching them and their results. 3. When identical messages (received within that time window, possibly "at the same time instant") are identified, avoid unnecessary duplicate computations. The framework would do this automatically, and essentially, the duplicate messages would never get received by a new actor for processing; they would silently vanish and the result from processing it once (whether that computation was already done in the past, or ongoing right then) would get sent to all appropriate recipients (immediately if already available, and upon completion of the computation if not). Note that messages should be considered identical even if the "reply" fields are different, as long as the semantics/computations they represent are identical in every other respect. Also note that the computation should be purely functional, i.e. free from side-effects, for the caching optimization suggested to work and not change the program semantics at all. If what I am suggesting is not compatible with the Akka way of doing things, and/or if you see some strong reasons why this is a very bad idea, please let me know. Thanks, Is Awesome, Scala

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• Is typeid of type name always evaluated at compile time in c++ ?

  - by cyril42e

  I wanted to check that typeid is evaluated at compile time when used with a type name (ie typeid(int), typeid(std::string)...). To do so, I repeated in a loop the comparison of two typeid calls, and compiled it with optimizations enabled, in order to see if the compiler simplified the loop (by looking at the execution time which is 1us when it simplifies instead of 160ms when it does not). And I get strange results, because sometimes the compiler simplifies the code, and sometimes it does not. I use g++ (I tried different 4.x versions), and here is the program: #include <iostream> #include <typeinfo> #include <time.h> class DisplayData {}; class RobotDisplay: public DisplayData {}; class SensorDisplay: public DisplayData {}; class RobotQt {}; class SensorQt {}; timespec tp1, tp2; const int n = 1000000000; int main() { int avg = 0; clock_gettime(CLOCK_REALTIME, &tp1); for(int i = 0; i < n; ++i) { // if (typeid(RobotQt) == typeid(RobotDisplay)) // (1) compile time // if (typeid(SensorQt) == typeid(SensorDisplay)) // (2) compile time if (typeid(RobotQt) == typeid(RobotDisplay) || typeid(SensorQt) == typeid(SensorDisplay)) // (3) not compile time ???!!! avg++; else avg--; } clock_gettime(CLOCK_REALTIME, &tp2); std::cout << "time (" << avg << "): " << (tp2.tv_sec-tp1.tv_sec)*1000000000+(tp2.tv_nsec-tp1.tv_nsec) << " ns" << std::endl; } The conditions in which this problem appear are not clear, but: - if there is no inheritance involved, no problem (always compile time) - if I do only one comparison, no problem - the problem only appears only with a disjunction of comparisons if all the terms are false So is there something I didn't get with how typeid works (is it always supposed to be evaluated at compilation time when used with type names?) or may this be a gcc bug in evaluation or optimization? About the context, I tracked down the problem to this very simplified example, but my goal is to use typeid with template types (as partial function template specialization is not possible). Thanks for your help!

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• Messing with the stack in assembly and c++

  - by user246100

  I want to do the following: I have a function that is not mine (it really doesn't matter here but just to say that I don't have control over it) and that I want to patch so that it calls a function of mine, preserving the arguments list (jumping is not an option). What I'm trying to do is, to put the stack pointer as it was before that function is called and then call mine (like going back and do again the same thing but with a different function). This doesn't work straight because the stack becomes messed up. I believe that when I do the call it replaces the return address. So, I did a step to preserve the return address saving it in a globally variable and it works but this is not ok because I want it to resist to recursitivy and you know what I mean. Anyway, i'm a newbie in assembly so that's why I'm here. Please, don't tell me about already made software to do this because I want to make things my way. Of course, this code has to be compiler and optimization independent. My code (If it is bigger than what is acceptable please tell me how to post it): // A function that is not mine but to which I have access and want to patch so that it calls a function of mine with its original arguments void real(int a,int b,int c,int d) { } // A function that I want to be called, receiving the original arguments void receiver(int a,int b,int c,int d) { printf("Arguments %d %d %d %d\n",a,b,c,d); } long helper; // A patch to apply in the "real" function and on which I will call "receiver" with the same arguments that "real" received. __declspec( naked ) void patch() { _asm { // This first two instructions save the return address in a global variable // If I don't save and restore, the program won't work correctly. // I want to do this without having to use a global variable mov eax, [ebp+4] mov helper,eax push ebp mov ebp, esp // Make that the stack becomes as it were before the real function was called add esp, 8 // Calls our receiver call receiver mov esp, ebp pop ebp // Restores the return address previously saved mov eax, helper mov [ebp+4],eax ret } } int _tmain(int argc, _TCHAR* argv[]) { FlushInstructionCache(GetCurrentProcess(),&real,5); DWORD oldProtection; VirtualProtect(&real,5,PAGE_EXECUTE_READWRITE,&oldProtection); // Patching the real function to go to my patch ((unsigned char*)real)[0] = 0xE9; *((long*)((long)(real) + sizeof(unsigned char))) = (char*)patch - (char*)real - 5; // calling real function (I'm just calling it with inline assembly because otherwise it seems to works as if it were un patched // that is strange but irrelevant for this _asm { push 666 push 1337 push 69 push 100 call real add esp, 16 } return 0; }

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• Select options not showing in IE

  - by donkapone

  I have a dynamically generated select with some options and it shows the options fine in normal browsers, but its empty options in IE. Here's the generated HTML: <select name="0" id="custom_0" style="border-bottom: #c0cedb 1px solid; border-left: #c0cedb 1px solid; background-color: #ededed; width: 280px; font-size: 0.87em; border-top: #c0cedb 1px solid; border-right: #c0cedb 1px solid"> <option id="1000" value="0" name="00">1x2GB ECC DDRIII 2GB ECC DDRIII</option> <option id="1001" value="10" name="01">2x2GB ECC DDRIII 4GB ECC DDRIII (+10.00 €)</option> </select> I can't really show you the javascript, since there's so much of it and I would be able to make it simple just for a demo. Maybe you had some of you would've had a similar experience and could figure this one out. Thanks I've added some javascript: $('#custom_order').append('<tr id="custom_'+category+'_row"><td'+padding+'>'+header+'<select id="custom_'+category+'" name="'+category+'" style="background-color:#EDEDED;border:1px solid #C0CEDB;width:280px;font-size:0.87em"></select>'+plusspan+'</td></tr>'); for (var i=0;i<components[category]['value'].length;i++){ $('#custom_'+category).append('<option id="'+components[category]['value'][i]['id']+'" value="'+components[category]['value'][i]['price']+'"></option>'); removals(category,i); dependencies(category,i); selectInput(category); } getDiff(category); getDiff() function adds the values to the options with html() function. The weird thing is, if I alert the html of the option just after the getDiff() function, it shows the value filled out. And it I put the getDiff() function in the for loop where the options are generated, it fills the values and shows them in IE, just not the last one. I'm calling getDiff() outside the loop for optimization, and since I can add the values later after all the options are generated. Well at least I thought I could, since it works on Firefox and Chrome.

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• jquery mouseent/leave to make div appears

  - by Blake

  I am looking to hover over my list item and have an effect similar to something like facebook chat is my best example..I am able to get the first div to appear but I believe this may be a selector issue because I cant get the rest working properly html <ul id="menu_seo" class="menu"> <li id="menu-seo"><span class="arrowout1"></span>SEO</li> <li id="menu-siteaudits"><span class="arrowout2"></span>Site Audits </li> <li id="menu-linkbuilding"><span class="arrowout3"></span>Link-Building</li> <li id="menu-localseo"><span class="arrowout4"></span>Local SEO</li> </ul> <div id="main_content"> <div id="menu-seo-desc"> <p>SEO management begins with a full website diagnosis of current web strategy Adjustments are made to improve your site’s ability to rank higher on search engines and draw more traffic </p> </div> <div id="menu-seo-desc2"> <p>Usability & site architecture review, Search Engine accessibility and indexing, Keyword research & targeting and Conversion rate optimization </p> </div> </div> css #menu-seo-desc { height:125px; width:210px; background-color:red; border-color:#CCC #E8E8E8 #E8E8E8 #CCC; border-style:solid; border-width:1.5px; border-radius:5px; box-shadow: 1px 0 2px 0px #888; -moz-box-shadow: 1px 0 2px 0px #888; -webkit-box-shadow: 1px 0 2px 1px #888; position:absolute; top:220px; left:350px; display:none; } js <script> $(document).ready(function(){ <script> $(document).ready(function(){ $('#menu_seo').on('#menu-seo', { 'mouseenter': function() { $('#menu-seo-desc').fadeIn(600); $('#menu-seo-desc2').fadeIn(600); }, 'mouseleave': function() { $('#menu-seo-desc').fadeOut(300); $('#menu-seo-desc2').fadeOut(300); } }); }); </script> });

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• Why Swift is 100 times slower than C in this image processing test?

  - by xiaobai

  Like many other developers I have been very excited at the new Swift language from Apple. Apple has boasted its speed is faster than Objective C and can be used to write operating system. And from what I learned so far, it's a very type-safe language and able to have precisely control over the exact data type (like integer length). So it does look like having good potential handling performance critical tasks, like image processing, right? That's what I thought before I carried out a quick test. The result really surprised me. Here is a much simplified image alpha blending code snippet in C: test.c: #include <stdio.h> #include <stdint.h> #include <string.h> uint8_t pixels[640*480]; uint8_t alpha[640*480]; uint8_t blended[640*480]; void blend(uint8_t* px, uint8_t* al, uint8_t* result, int size) { for(int i=0; i<size; i++) { result[i] = (uint8_t)(((uint16_t)px[i]) *al[i] /255); } } int main(void) { memset(pixels, 128, 640*480); memset(alpha, 128, 640*480); memset(blended, 255, 640*480); // Test 10 frames for(int i=0; i<10; i++) { blend(pixels, alpha, blended, 640*480); } return 0; } I compiled it on my Macbook Air 2011 with the following command: gcc -O3 test.c -o test The 10 frame processing time is about 0.01s. In other words, it takes the C code 1ms to process one frame: $ time ./test real 0m0.010s user 0m0.006s sys 0m0.003s Then I have a Swift version of the same code: test.swift: let pixels = UInt8[](count: 640*480, repeatedValue: 128) let alpha = UInt8[](count: 640*480, repeatedValue: 128) let blended = UInt8[](count: 640*480, repeatedValue: 255) func blend(px: UInt8[], al: UInt8[], result: UInt8[], size: Int) { for(var i=0; i<size; i++) { var b = (UInt16)(px[i]) * (UInt16)(al[i]) result[i] = (UInt8)(b/255) } } for i in 0..10 { blend(pixels, alpha, blended, 640*480) } The build command line is: xcrun swift -O3 test.swift -o test Here I use the same O3 level optimization flag to make the comparison hopefully fair. However, the resulting speed is 100 time slower: $ time ./test real 0m1.172s user 0m1.146s sys 0m0.006s In other words, it takes Swift ~120ms to processing one frame which takes C just 1 ms. I also verified the memory initialization time in both test code are very small compared to the blend processing function time. What happened?

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