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  • Working with Temporal Data in SQL Server

    - by Dejan Sarka
    My third Pluralsight course, Working with Temporal Data in SQL Server, is published. I am really proud on the second part of the course, where I discuss optimization of temporal queries. This was a nearly impossible task for decades. First solutions appeared only lately. I present all together six solutions (and one more that is not a solution), and I invented four of them. http://pluralsight.com/training/Courses/TableOfContents/working-with-temporal-data-sql-server

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  • Is there something special about the number 65535?

    - by Nick Rosencrantz
    2¹6-1 & 25 = 25 (or? obviously ?) A developer asked me today what is bitwise 65535 & 32 i.e. 2¹6-1 & 25 = ? I thought at first spontaneously 32 but it seemed to easy whereupon I thought for several minutes and then answered 32. 32 seems to have been the correct answer but how? 65535=2¹6-1=1111111111111111 (but it doesn't seem right since this binary number all ones should be -1(?)), 32 = 100000 but I could not convert that in my head whereupon I anyway answered 32 since I had to answer something. Is the answer 32 in fact trivial? Is in the same way 2¹6-1 & 25-1 =31? Why did the developer ask me about exactly 65535? Binary what I was asked to evaluate was 1111111111111111 & 100000 but I don't understand why 1111111111111111 is not -1. Shouldn't it be -1? Is 65535 a number that gives overflow and how do I know that?

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  • What kind of specific projects can I do to master bitwise operations in C++? Also is there a canonical book? [closed]

    - by Ford
    I don't use C++ or bitwise operations at my current job but I'm thinking of applying to companies where it is a requirement to be fluent with them (on their tests anyway). So my question is: Can anyone suggest a project which will require gaining a fluency in bitwise operations to complete? On a side note, is there a canonical book on optimization techniques using bitwise operations since that seems to be an important use of them?

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  • Is Operator Overloading supported in C

    - by caramel23
    Today when I was reading about LCC(windows) compiler I find out it has the implemention for operator overloading . I'm puzzled because after a bit of googling , it has been confirm that operator overloading ain't support in standard C , but I read some people's comment mentioning LCC is ANSI-compliant . So my real question is , is LCC really standard C or it's just like objective-c , a C variant with object-oriented feature ?

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  • Concept of bit fields

    - by user1369975
    Whenever I read a code like this: struct node { int x : 2; int p : 4; }n; with bit fields involved, I get really confused, as to how they are represented in memory, what is sizeof(n) etc., how does it differ with normal members of structures? I tried referring K&R and http://en.wikipedia.org/wiki/Bit_field but they little to remove my confusion. What concepts of bit fields am I failing to grasp?

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  • Is there anyway to close a StreamWriter without closing it's BaseStream?

    - by Binary Worrier
    My root problem is that when using calls Dispose on a StreamWriter, it also disposes the BaseStream (same problem with Close). I have a workaround for this, but as you can see it involves copying the stream. Is there any way to do this without copying the stream? The purpose of this is to get the contents of a string (originally read from a database) into a stream, so the stream can be read by a third party component. NB I cannot change the third party component. public System.IO.Stream CreateStream(string value) { var baseStream = new System.IO.MemoryStream(); var baseCopy = new System.IO.MemoryStream(); using (var writer = new System.IO.StreamWriter(baseStream, System.Text.Encoding.UTF8)) { writer.Write(value); writer.Flush(); baseStream.WriteTo(baseCopy); } baseCopy.Seek(0, System.IO.SeekOrigin.Begin); return baseCopy; } Used as public void Noddy() { System.IO.Stream myStream = CreateStream("The contents of this string are unimportant"); My3rdPartyComponent.ReadFromStream(myStream); } Ideally I'm looking for an imaginery method called BreakAssociationWithBaseStream, e.g. public System.IO.Stream CreateStream_Alternate(string value) { var baseStream = new System.IO.MemoryStream(); using (var writer = new System.IO.StreamWriter(baseStream, System.Text.Encoding.UTF8)) { writer.Write(value); writer.Flush(); writer.BreakAssociationWithBaseStream(); } return baseStream; }

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  • Efficient (basic) regular expression implementation for streaming data

    - by Brendan Dolan-Gavitt
    I'm looking for an implementation of regular expression matching that operates on a stream of data -- i.e., it has an API that allows a user to pass in one character at a time and report when a match is found on the stream of characters seen so far. Only very basic (classic) regular expressions are needed, so a DFA/NFA based implementation seems like it would be well-suited to the problem. Based on the fact that it's possible to do regular expression matching using a DFA/NFA in a single linear sweep, it seems like a streaming implementation should be possible. Requirements: The library should try to wait until the full string has been read before performing the match. The data I have really is streaming; there is no way to know how much data will arrive, it's not possible to seek forward or backward. Implementing specific stream matching for a couple special cases is not an option, as I don't know in advance what patterns a user might want to look for. For the curious, my use case is the following: I have a system which intercepts memory writes inside a full system emulator, and I would like to have a way to identify memory writes that match a regular expression (e.g., one could use this to find the point in the system where a URL is written to memory). I have found (links de-linkified because I don't have enough reputation): stackoverflow.com/questions/1962220/apply-a-regex-on-stream stackoverflow.com/questions/716927/applying-a-regular-expression-to-a-java-i-o-stream www.codeguru.com/csharp/csharp/cs_data/searching/article.php/c14689/Building-a-Regular-Expression-Stream-Search-with-the-NET-Framework.htm But all of these attempt to convert the stream to a string first and then use a stock regular expression library. Another thought I had was to modify the RE2 library, but according to the author it is architected around the assumption that the entire string is in memory at the same time. If nothing's available, then I can start down the unhappy path of reinventing this wheel to fit my own needs, but I'd really rather not if I can avoid it. Any help would be greatly appreciated!

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  • Can mediatomb VLC profile transcode audio as MP3 rather than mpga ?

    - by djangofan
    In the /etc/mediatomb/config.xml, can mediatomb VLC profile transcode audo as MP3 rather than mpga ? My Sony GoogleTV wont render streamed .avi files files with a mpga audio in them. The original files are Divx encoded with 128kbs MP3 audio but mediatomb is transcoding them. How can I change this? Any ideas? Can I turn off the audio and video transcoding somehow? I need some ideas to try. <profile name="vlcprof" enabled="yes" type="external"> <mimetype>video/mpeg</mimetype> <agent command="vlc" arguments="-I dummy %in --sout #transcode{venc=ffmpeg,vcodec=mp2v,vb=4096,fps=25,aenc=ffmpeg,acodec=mpga,ab=192,samplerate=44100,channels=2}:standard{access=file,mux=ps,dst=%out} vlc:quit"/> <buffer size="10485760" chunk-size="131072" fill-size="2621440"/> <accept-url>yes</accept-url> <first-resource>yes</first-resource> </profile> I know that that MP3 encoding support is external to FFmpeg and must be configured appropriately, but I have no idea how to handle that. I would guess I can work around that by somehow telling ffmpeg to not transcode the audio stream? Also, should I create a separate vlcprof entry for video/avi ? Can you create more than one profile for VLC in the config.xml for mediatomb?

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  • What are my options for sharing music between Windows & Ubuntu on the same network?

    - by jgbelacqua
    We have a few Windows(XP & 7) and Ubuntu machines in the house sharing a wireless connection, and want to share music between them. If possible, I would like to be able to serve music from both Windows and Ubuntu (but it doesn't have to be the same time). I don't know much about sharing folders or streaming, but I'm guessing both would be options (that is, using a local client to access a shared song or a local client to access a shared stream). I want to be able to share the music between the systems as simply as possible. Bonus points (but not requirements) for cross-platform -- same application on both Windows and Ubuntu? available on startup (via daemon or autostart or whatnot) open source More info: All systems have dynamic addresses (DHCP) supplied from the ISP-supplied wireless router. There are several Gigabytes of music on one Windows XP box and one Ubuntu 10.10 The music is not well-sorted (I'm thinking this might have an impact on UI usability). Only has to be available internally (private address space behind the wireless router) bandwidth is not a problem We don't have (legitimate) admin access to the wireless router

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  • VLC (Server) re-stream Security Camera Feed

    - by Aaron
    I purchased a Swann Home Security DVR system and was hoping for some help on how to duplicate the streaming video on my server. In order to get their web view (streaming video in the browser) to work, I had to install the following plugins: HiDvrPlugin.dmg for mac. Hidvrocx.cab for Windows. I was originally thinking it was a sign of some form of DRM? Maybe. Maybe not. HTML wise, the following code is in the source of the safari version of the web view: <embed pluginspage="SurveilClient.dmg" width="10px" height="10px" type="application/x-scplugin" id="MacDiv" style="height: 592px; width: 720px; left: 278px; top: 61px; "> It seems to be the main display area. Using wireshark, I am able to see that the video stream is on port 9000. However, I have no idea what type of stream it is. I've tried opening it in VLC with no such luck. http://dvr_ip:9000 tcp://dvr_ip:9000 My hope was to do the following to redistribute the feed vlc dvr_ip:9000 --sout h264-version-on-localhost:3000 TLDR; Trying to re-distribute a stream from a security camera (can't tell the format) using vlc (re-distribute via h.264 / HTML5). Not sure how to accomplish this. Is it possible that the software has some type of DRM that only the plugins can decode?

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  • Nginx flv audio pseudo stream works but video is not loading

    - by sarah
    I am working on a development server for a company & they want nginx webserver to work with. So the requirements for their company is, it should be capable of doing following things i.e hotlink protection, mp4 & flv pseudo stream & secure streaming. However nginx fulfills their requirements and i am configuring their server from past 2 days as i am new to this field so i've only acheived hotlinking prevention in past 2 days. But the problem on which i am stuck is flv pseudo streaming, to make work to mp4 pseudo stream it was just a piece of paper but i am really fuc*ed up with flv pseudo stream. I have converted my flv videos with flvmdi tools to insert many keyframes but the problem is , when i try to seek video from following keyframes that are generated by flvmdi i.e test.flv?start=2681223, video does not load but audio pseudo works fine. So it means no problem with my flv configuration in nginx.conf file. And the forum that i used to compile my nginx-1.2.1 is http://h264.code-shop.com/trac/wiki/Mod-H264-Streaming-Nginx-Version2 & by adding additional module --with-http_flv_module. This forum is really active, hopes i will resolve my problem as soon as you guys will provide me some guide.

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  • How to stream H264 Video from camera over FTP?

    - by Jay
    I bought a h264 security camera system last year and set it up to ftp video to my computer. I was able to get the video to play (even though it played a little fast) on Ubuntu 11.04 using mplayer. A few months ago, I did a fresh install of 12.04 and I cannot seem to get the video to play with mplayer, smplayer or VLC. I have the restricted formats video packages installed and when playing with any of the players, all I get is a gray video. When calling mplayer from the command line to play the video with no options, I get a lot of these errors: [h264 @ 0x7f278c61f280]concealing 1320 DC, 1320 AC, 1320 MV errors No pts value from demuxer to use for frame! pts after filters MISSING I'm not a video expert and have been coming up with a lot of dead ends when Googling for this. Could someone offer some advice about how to play these videos? Here is the output of mediainfo for a sample file. mediainfo -f sec-cam01-m-20120921-212454.h264 General Count : 278 Count of stream of this kind : 1 Kind of stream : General Kind of stream : General Stream identifier : 0 Count of video streams : 1 Video_Format_List : AVC Video_Format_WithHint_List : AVC Codecs Video : AVC Complete name : sec-cam01-m-20120921-212454.h264 File name : sec-cam01-m-20120921-212454 File extension : h264 Format : AVC Format : AVC Format/Info : Advanced Video Codec Format/Url : http://developers.videolan.org/x264.html Format/Extensions usually used : avc h264 Commercial name : AVC Internet media type : video/H264 Codec : AVC Codec : AVC Codec/Info : Advanced Video Codec Codec/Url : http://developers.videolan.org/x264.html Codec/Extensions usually used : avc h264 File size : 1097315 File size : 1.05 MiB File size : 1 MiB File size : 1.0 MiB File size : 1.05 MiB File size : 1.046 MiB File last modification date : UTC 2012-09-22 01:27:12 File last modification date (local) : 2012-09-21 21:27:12 Video Count : 205 Count of stream of this kind : 1 Kind of stream : Video Kind of stream : Video Stream identifier : 0 Format : AVC Format/Info : Advanced Video Codec Format/Url : http://developers.videolan.org/x264.html Commercial name : AVC Format profile : [email protected] Format settings : 1 Ref Frames Format settings, CABAC : No Format settings, CABAC : No Format settings, ReFrames : 1 Format settings, ReFrames : 1 frame Format settings, GOP : M=1, N=3 Internet media type : video/H264 Codec : AVC Codec : AVC Codec/Family : AVC Codec/Info : Advanced Video Codec Codec/Url : http://developers.videolan.org/x264.html Codec profile : [email protected] Codec settings : 1 Ref Frames Codec settings, CABAC : No Codec_Settings_RefFrames : 1 Width : 704 Width : 704 pixels Height : 480 Height : 480 pixels Pixel aspect ratio : 1.000 Display aspect ratio : 1.467 Display aspect ratio : 3:2 Standard : NTSC Resolution : 8 Resolution : 8 bits Colorimetry : 4:2:0 Color space : YUV Chroma subsampling : 4:2:0 Bit depth : 8 Bit depth : 8 bits Scan type : Progressive Scan type : Progressive Interlacement : PPF Interlacement : Progressive Edit: Here is a sample video using the same encoding: https://www.dropbox.com/s/l5acwzy8rtqn9xe/sec-cam08-m-20121118-105815.h264 (not the same video as mediainfo output)

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  • FFSERVER - streaming an ASF video as Webm output

    - by Emmanuel Brunet
    I'm trying to stream an IP webcam ASF live stream to a ffserver to output a webm video format. The server starts successfully but the ffserver commands used to feed the ffserver fails and generates a core dump. Environment Debian 7.5 ffmpeg 2.2 Input stream $ ffprobe http://account:password@webcam/videostream.asf Input #0, asf, from 'http://admin:alpha1237@webcam/videostream.asf': Duration: N/A, start: 0.000000, bitrate: 32 kb/s Stream #0:0: Video: mjpeg (MJPG / 0x47504A4D), yuvj422p(pc), 640x480, 25 tbr, 1k tbn, 1k tbc Stream #0:1: Audio: adpcm_ima_wav ([17][0][0][0] / 0x0011), 8000 Hz, 1 channels, s16p, 32 kb/s ffserver configuration my ffserver configuration is : Port 8091 RTSPPort 554 BindAddress 192.168.1.62 MaxHTTPConnections 1000 MaxClients 100 MaxBandwidth 1000 CustomLog - <Feed webcam.ffm> File /tmp/webcam.ffm FileMaxSize 500M ACL allow localhost ACL allow 192.168.0.0 192.168.255.255 </Feed> <Stream webcam.webm> # Output stream URL definition Feed webcam.ffm # Feed from which to receive video Format webm # Audio settings AudioCodec vorbis AudioBitRate 64 # Audio bitrate # Video settings VideoCodec libvpx VideoSize 640x480 # Video resolution VideoFrameRate 25 # Video FPS AVOptionVideo flags +global_header # Parameters passed to encoder # (same as ffmpeg command-line parameters) AVOptionVideo cpu-used 0 AVOptionVideo qmin 10 AVOptionVideo qmax 42 AVOptionVideo quality good AVOptionAudio flags +global_header PreRoll 15 StartSendOnKey # VideoBitRate 32 # Video bitrate </Stream> <Stream status.html> Format status # Only allow local people to get the status ACL allow localhost ACL allow 192.168.0.0 192.168.255.255 </Stream> ffmpeg feed I run the following command that fails $ ffmpeg -i http://account:password@webcam/videostream.asf http://192.168.1.62:8091/webcam.ffm http://192.168.1.62:8091/webcam.ffm Input #0, asf, from 'http://account:password@webcam/videostream.asf': Duration: N/A, start: 0.000000, bitrate: 32 kb/s Stream #0:0: Video: mjpeg (MJPG / 0x47504A4D), yuvj422p(pc), 640x480, 25 tbr, 1k tbn, 1k tbc Stream #0:1: Audio: adpcm_ima_wav ([17][0][0][0] / 0x0011), 8000 Hz, mono, s16p, 32 kb/s [swscaler @ 0x36a80c0] deprecated pixel format used, make sure you did set range correctly Segmentation fault I tryed $ ffmpeg -i http://account:password@webcam/videostream.asf -pix_fmt yuv420p http://192.168.1.62:8091/webcam.ffm But it raises the same error. Thanks for your help Edit For an easy testing (I thought), I tried to publish the whole ASF stream as is, meaning connecting the ASF webcam output stream to the ffserver that outputs ASF format too. And thus with mirrored encoding so I changed the ffserver configuration to ... <Stream webcam.asf> Feed webcam.ffm Format asf VideoFrameRate 25 VideoSize 640X480 VideoBitRate 256 VideoBufferSize 1000 VideoGopSize 30 AudioBitRate 32 StartSendOnKey </Stream> ... And the output is now : Input #0, asf, from 'http://admin:alpha1237@webcam/videostream.asf': Duration: N/A, start: 0.000000, bitrate: 32 kb/s Stream #0:0: Video: mjpeg (MJPG / 0x47504A4D), yuvj422p(pc), 640x480, 1k tbr, 1k tbn, 1k tbc Stream #0:1: Audio: adpcm_ima_wav ([17][0][0][0] / 0x0011), 8000 Hz, mono, s16p, 32 kb/s [swscaler @ 0x3d620c0] deprecated pixel format used, make sure you did set range correctly Output #0, ffm, to 'http://192.168.1.62:8091/webcam.ffm': Metadata: creation_time : now encoder : Lavf55.40.100 Stream #0:0: Audio: wmav2, 22050 Hz, mono, fltp, 32 kb/s Metadata: encoder : Lavc55.64.100 wmav2 Stream #0:1: Video: msmpeg4v3 (msmpeg4), yuv420p, 640x480, q=2-31, 256 kb/s, 1k fps, 1000k tbn, 1k tbc Metadata: Stream mapping: Stream #0:1 -> #0:0 (adpcm_ima_wav -> wmav2) Stream #0:0 -> #0:1 (mjpeg -> msmpeg4) Press [q] to stop, [?] for help Segmentation fault I can't even forward the stream.

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  • ffserver-2.2 - streaming an ASF video as Webm output with ffserver on Debian 7.5

    - by Emmanuel Brunet
    I'm trying to stream an IP webcam ASF live stream to a ffserver to output a webm video format. The server starts successfully but the ffserver commands used to feed the ffserver fails and generates a core dump. Input stream $ ffprobe http://account:password@webcam/videostream.asf Input #0, asf, from 'http://account:password@webcam/videostream.asf': Duration: N/A, start: 0.000000, bitrate: 32 kb/s Stream #0:0: Video: mjpeg (MJPG / 0x47504A4D), yuvj422p(pc), 640x480, 25 tbr, 1k tbn, 1k tbc Stream #0:1: Audio: adpcm_ima_wav ([17][0][0][0] / 0x0011), 8000 Hz, 1 channels, s16p, 32 kb/s ffserver configuration my ffserver configuration is : Port 8091 RTSPPort 554 BindAddress 192.168.1.62 MaxHTTPConnections 1000 MaxClients 100 MaxBandwidth 1000 CustomLog - <Feed webcam.ffm> File /tmp/webcam.ffm FileMaxSize 500M ACL allow localhost ACL allow 192.168.0.0 192.168.255.255 </Feed> <Stream webcam.webm> # Output stream URL definition Feed webcam.ffm # Feed from which to receive video Format webm # Audio settings AudioCodec vorbis AudioBitRate 64 # Audio bitrate # Video settings VideoCodec libvpx VideoSize 640x480 # Video resolution VideoFrameRate 25 # Video FPS AVOptionVideo flags +global_header # Parameters passed to encoder # (same as ffmpeg command-line parameters) AVOptionVideo cpu-used 0 AVOptionVideo qmin 10 AVOptionVideo qmax 42 AVOptionVideo quality good AVOptionAudio flags +global_header PreRoll 15 StartSendOnKey # VideoBitRate 32 # Video bitrate </Stream> <Stream status.html> Format status # Only allow local people to get the status ACL allow localhost ACL allow 192.168.0.0 192.168.255.255 </Stream> ffmpeg feed I run the following command that fails $ ffmpeg -i http://account:password@webcam/videostream.asf http://ffserver_ip:port/webcam.ffm http://192.168.1.62:8091/webcam.ffm Input #0, asf, from 'http://account:password@webcam/videostream.asf': Duration: N/A, start: 0.000000, bitrate: 32 kb/s Stream #0:0: Video: mjpeg (MJPG / 0x47504A4D), yuvj422p(pc), 640x480, 25 tbr, 1k tbn, 1k tbc Stream #0:1: Audio: adpcm_ima_wav ([17][0][0][0] / 0x0011), 8000 Hz, mono, s16p, 32 kb/s [swscaler @ 0x36a80c0] deprecated pixel format used, make sure you did set range correctly Segmentation fault I tryed $ ffmpeg -i http://account:password@webcam/videostream.asf -pix_fmt yuv420p http://ffserver_ip:port/webcam.ffm But it raises the same error. Thanks for your help Edit For an easy testing (I thought), I tried to publish the whole ASF stream as is, meaning connecting the ASF webcam output stream to the ffserver that outputs ASF format too. And thus with mirrored encoding so I changed the ffserver configuration to ... <Stream webcam.asf> Feed webcam.ffm Format asf VideoFrameRate 25 VideoSize 640X480 VideoBitRate 256 VideoBufferSize 1000 VideoGopSize 30 AudioBitRate 32 StartSendOnKey </Stream> ... And the output is now : Input #0, asf, from 'http://admin:alpha1237@webcam/videostream.asf': Duration: N/A, start: 0.000000, bitrate: 32 kb/s Stream #0:0: Video: mjpeg (MJPG / 0x47504A4D), yuvj422p(pc), 640x480, 1k tbr, 1k tbn, 1k tbc Stream #0:1: Audio: adpcm_ima_wav ([17][0][0][0] / 0x0011), 8000 Hz, mono, s16p, 32 kb/s [swscaler @ 0x3d620c0] deprecated pixel format used, make sure you did set range correctly Output #0, ffm, to 'http://192.168.1.62:8091/webcam.ffm': Metadata: creation_time : now encoder : Lavf55.40.100 Stream #0:0: Audio: wmav2, 22050 Hz, mono, fltp, 32 kb/s Metadata: encoder : Lavc55.64.100 wmav2 Stream #0:1: Video: msmpeg4v3 (msmpeg4), yuv420p, 640x480, q=2-31, 256 kb/s, 1k fps, 1000k tbn, 1k tbc Metadata: Stream mapping: Stream #0:1 -> #0:0 (adpcm_ima_wav -> wmav2) Stream #0:0 -> #0:1 (mjpeg -> msmpeg4) Press [q] to stop, [?] for help Segmentation fault I can't even forward the stream. Thanks for your help again.

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  • Suggested GA operators for a TSP problem?

    - by Mark
    I'm building a genetic algorithm to tackle the traveling salesman problem. Unfortunately, I hit peaks that can sustain for over a thousand generations before mutating out of them and getting better results. What crossover and mutation operators generally do well in this case?

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  • How to make ARGB transparency using bitwise operators.

    - by Smejda
    I need to make transparency, having 2 pixels: pixel1: {A, R, G, B} - foreground pixel pixel2: {A, R, G, B} - background pixel A,R,G,B are Byte values each color is represented by byte value now I'm calculating transparency as: newR = pixel2_R * alpha / 255 + pixel1_R * (255 - alpha) / 255 newG = pixel2_G * alpha / 255 + pixel1_G * (255 - alpha) / 255 newB = pixel2_B * alpha / 255 + pixel1_B * (255 - alpha) / 255 but it is too slow I need to do it with bitwise operators (AND,OR,XOR, NEGATION, BIT MOVE)

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  • Containers of reference_wrappers (comparison operators required?)

    - by kloffy
    If you use stl containers together with reference_wrappers of POD types, the following code works just fine: int i = 3; std::vector< boost::reference_wrapper<int> > is; is.push_back(boost::ref(i)); std::cout << (std::find(is.begin(),is.end(),i)!=is.end()) << std::endl; However, if you use non-POD types such as (contrived example): struct Integer { int value; bool operator==(const Integer& rhs) const { return value==rhs.value; } bool operator!=(const Integer& rhs) const { return !(*this == rhs); } }; It doesn't suffice to declare those comparison operators, instead you have to declare: bool operator==(const boost::reference_wrapper<Integer>& lhs, const Integer& rhs) { return boost::unwrap_ref(lhs)==rhs; } And possibly also: bool operator==(const Integer& lhs, const boost::reference_wrapper<Integer>& rhs) { return lhs==boost::unwrap_ref(rhs); } In order to get the equivalent code to work: Integer j = { 0 }; std::vector< boost::reference_wrapper<Integer> > js; js.push_back(boost::ref(j)); std::cout << (std::find(js.begin(),js.end(),j)!=js.end()) << std::endl; Now, I'm wondering if this is really the way it's meant to be done, since it seems impractical. It just seems there should be a simpler solution, e.g. templates: template<class T> bool operator==(const boost::reference_wrapper<T>& lhs, const T& rhs) { return boost::unwrap_ref(lhs)==rhs; } template<class T> bool operator==(const T& lhs, const boost::reference_wrapper<T>& rhs) { return lhs==boost::unwrap_ref(rhs); } There's probably a good reason why reference_wrapper behaves the way it does (possibly to accomodate non-POD types without comparison operators?). Maybe there already is an elegant solution and I just haven't found it.

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  • PL/SQL Logical Operators evaluate whole function

    - by Chris
    I know in C like languages logical operators are evaluated one at a time so: false && really_expensive_function() is doesn't result in the function being called (I can't remember the CS name for this). Does the same happen in PL/SQL or do I need to break the IF parts out to separate blocks?

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  • How to pass operators as parameters

    - by Rodion Ingles
    I have to load an array of doubles from a file, multiply each element by a value in a table (different values for different elements), do some work on it, invert the multiplication (that is, divide) and then save the data back to file. Currently I implement the multiplication and division process in two separate methods. Now there is some extra work behind the scenes but apart from the specific statements where the multiplication/division occurs, the rest of the code is identical. As you can imagine, with this approach you have to be very careful making any changes. The surrounding code is not trivial, so its either a case of manually editing each method or copying changes from one method to the other and remembering to change the * and / operators. After too many close calls I am fed up of this and would like to make a common function which implements the common logic and two wrapper functions which pass which operator to use as a parameter. My initial approach was to use function pointers: MultiplyData(double data) { TransformData(data, &(operator *)); } DivideData(double data) { TransformData(data, &(operator /)); } TransformData(double data, double (*func)(double op1, double op2)) { /* Do stuff here... */ } However, I can't pass the operators as pointers (is this because it is an operator on a native type?), so I tried to use function objects. Initially I thought that multiplies and divides functors in <functional> would be ideal: MultiplyData(double data) { std::multiplies<double> multFunct; TransformData(data, &multFunct); } DivideData(double data) { std::divides<double> divFunct; TransformData(data, &divFunct); } TransformData(double data, std::binary_function<double, double, double> *funct) { /* Do stuff here... */ } As you can see I was trying to use a base class pointer to pass the functor polymorphically. The problem is that std::binary_function does not declare an operator() member for the child classes to implement. Is there something I am missing, or is the solution to implement my own functor heirarchy (which really seems more trouble than it is worth)?

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  • Some questions about writing on ASP.NET response stream

    - by vtortola
    Hi, I'm making tests with ASP.NET HttpHandler for download a file writting directly on the response stream, and I'm not pretty sure about the way I'm doing it. This is a example method, in the future the file could be stored in a BLOB in the database: public void GetFile(HttpResponse response) { String fileName = "example.iso"; response.ClearHeaders(); response.ClearContent(); response.ContentType = "application/octet-stream"; response.AppendHeader("Content-Disposition", "attachment; filename=" + fileName); using (FileStream fs = new FileStream(Path.Combine(HttpContext.Current.Server.MapPath("~/App_Data"), fileName), FileMode.Open)) { Byte[] buffer = new Byte[4096]; Int32 readed = 0; while ((readed = fs.Read(buffer, 0, buffer.Length)) > 0) { response.OutputStream.Write(buffer, 0, readed); response.Flush(); } } } But, I'm not sure if this is correct or there is a better way to do it. My questions are: When I open the url with the browser, appears the "Save File" dialog... but it seems like the server has started already to push data into the stream before I click "Save", is that normal? If I remove the line"response.Flush()", when I open the url with the browser, ... I see how the web server is pushing data but the "Save File" dialog doesn't come up, (or at least not in a reasonable time fashion) why? When I open the url with a WebRequest object, I see that the HttpResponse.ContentLength is "-1", although I can read the stream and get the file. What is the meaning of -1? When is HttpResponse.ContentLength going to show the length of the response? For example, I have a method that retrieves a big xml compresed with deflate as a binary stream, but in that case... when I access it with a WebRequest, in the HttpResponse I can actually see the ContentLength with the length of the stream, why? What is the optimal length for the Byte[] array that I use as buffer for optimal performance in a web server? I've read that is between 4K and 8K... but which factors should I consider to make the correct decision. Does this method bloat the IIS or client memory usage? or is it actually buffering the transference correctly? Sorry for so many questions, I'm pretty new in web development :P Cheers.

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  • Silverlight changes the io.Stream to byte[]

    - by Sai
    I have created a WCF service for uploading images , which accepts System.IO.Stream as input parameter and am using streaming. When I added the service reference in Silverlight project then it automatically changed the parameter of my WCF method from System.IO.Stream to byte[]. Can anyone suggest if there is a way around this so that I can get System.IO.Stream type rather than byte[]. Thanks in advance

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  • Json HTTP Module stream issue

    - by Justin
    Hey, I have an HTTP Module that I use to clean up the JSON returned by my web service (see http://www.codeproject.com/KB/webservices/ASPNET_JSONP.aspx?msg=3400287#xx3400287xx for an example of this.) Basically it relates to calling cross-domain JSON web services from javascript. There is this JsonHttpModule which uses a JsonResponseFilter Stream class to write out the JSON and the overloaded Write method is supposed to wrap the name of the callback function around the JSON, otherwise the JSON errors out as needing a label. However, if the JSON is really long, the Write method in the Stream class is called multiple times, causing the callback function to incorrectly get inserted midway through the JSON. Is there a way in the Stream class to wrap the callback function around the stream at the end or to specify that it write all of the JSON in 1 Write method instead of in chunks?? Here's where it calls the JsonResponseFilter in the JsonHttpModule: public void OnReleaseRequestState(object sender, EventArgs e) { HttpApplication app = (HttpApplication)sender; if (!_Apply(app.Context.Request)) return; // apply response filter to conform to JSONP app.Context.Response.Filter = new JsonResponseFilter(app.Context.Response.Filter, app.Context); } Here's the Write method in the JsonResponseFilter Stream class that gets called multiple times: public override void Write(byte[] buffer, int offset, int count) { var b1 = Encoding.UTF8.GetBytes(_context.Request.Params["callback"] + "("); _responseStream.Write(b1, 0, b1.Length); _responseStream.Write(buffer, offset, count); var b2 = Encoding.UTF8.GetBytes(");"); _responseStream.Write(b2, 0, b2.Length); } Thanks for any help! Justin

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  • Can i write to data output stream after reading response from data input stream?

    - by Sirius
    Hi, i want to do a client-server activity like this: 1. first the client sends/writes to output stream 2. the server responses with some data that will be read with input stream 3. after receiving the data, the client sends/writes to output stream again to respond that the data has been received now, do i have to close the output stream and re-open it again before doing step no.3 ? also if someone could provide me with a snippet, it would be really helpful. thanks

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