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  • Best way to do powerOf(int x, int n)?

    - by Mike
    So given x, and power, n, solve for X^n. There's the easy way that's O(n)... I can get it down to O(n/2), by doing numSquares = n/2; numOnes = n%2; return (numSquares * x * x + numOnes * x); Now there's a log(n) solution, does anyone know how to do it? It can be done recursively.

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  • Continuation - Viewing FIRST_ROWS before query completes.

    - by Frank Developer
    I have identified the query constructs my users normally use. would it make sense for me to create composite indexes to support those constructs and provide FIRST_ROWS capability? If I migrate from SE to IDS, I will loose the ability to write low-level functions with c-isam calls, but gain FIRST_ROWS along with other goodies like: SET-READS for index scans (onconfig USE_[KO]BATCHEDREAD), optimizer directives, parallel queries, etc?

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  • Autocorrelation returns random results with mic input (using a high pass filter)

    - by Niall
    Hello, Sorry to ask a similar question to the one i asked before (FFT Problem (Returns random results)), but i've looked up pitch detection and autocorrelation and have found some code for pitch detection using autocorrelation. Im trying to do pitch detection of a users singing. Problem is, it keeps returning random results. I've got some code from http://code.google.com/p/yaalp/ which i've converted to C++ and modified (below). My sample rate is 2048, and data size is 1024. I'm detecting pitch of both a sine wave and mic input. The frequency of the sine wave is 726.0, and its detecting it to be 722.950820 (which im ok with), but its detecting the pitch of the mic as a random number from around 100 to around 1050. I'm now using a High pass filter to remove the DC offset, but it's not working. Am i doing it right, and if so, what else can i do to fix it? Any help would be greatly appreciated! double* doHighPassFilter(short *buffer) { // Do FFT: int bufferLength = 1024; float *real = malloc(bufferLength*sizeof(float)); float *real2 = malloc(bufferLength*sizeof(float)); for(int x=0;x<bufferLength;x++) { real[x] = buffer[x]; } fft(real, bufferLength); for(int x=0;x<bufferLength;x+=2) { real2[x] = real[x]; } for (int i=0; i < 30; i++) //Set freqs lower than 30hz to zero to attenuate the low frequencies real2[i] = 0; // Do inverse FFT: inversefft(real2,bufferLength); double* real3 = (double*)real2; return real3; } double DetectPitch(short* data) { int sampleRate = 2048; //Create sine wave double *buffer = malloc(1024*sizeof(short)); double amplitude = 0.25 * 32768; //0.25 * max length of short double frequency = 726.0; for (int n = 0; n < 1024; n++) { buffer[n] = (short)(amplitude * sin((2 * 3.14159265 * n * frequency) / sampleRate)); } doHighPassFilter(data); printf("Pitch from sine wave: %f\n",detectPitchCalculation(buffer, 50.0, 1000.0, 1, 1)); printf("Pitch from mic: %f\n",detectPitchCalculation(data, 50.0, 1000.0, 1, 1)); return 0; } // These work by shifting the signal until it seems to correlate with itself. // In other words if the signal looks very similar to (signal shifted 200 data) than the fundamental period is probably 200 data // Note that the algorithm only works well when there's only one prominent fundamental. // This could be optimized by looking at the rate of change to determine a maximum without testing all periods. double detectPitchCalculation(double* data, double minHz, double maxHz, int nCandidates, int nResolution) { //-------------------------1-------------------------// // note that higher frequency means lower period int nLowPeriodInSamples = hzToPeriodInSamples(maxHz, 2048); int nHiPeriodInSamples = hzToPeriodInSamples(minHz, 2048); if (nHiPeriodInSamples <= nLowPeriodInSamples) printf("Bad range for pitch detection."); if (1024 < nHiPeriodInSamples) printf("Not enough data."); double *results = new double[nHiPeriodInSamples - nLowPeriodInSamples]; //-------------------------2-------------------------// for (int period = nLowPeriodInSamples; period < nHiPeriodInSamples; period += nResolution) { double sum = 0; // for each sample, find correlation. (If they are far apart, small) for (int i = 0; i < 1024 - period; i++) sum += data[i] * data[i + period]; double mean = sum / 1024.0; results[period - nLowPeriodInSamples] = mean; } //-------------------------3-------------------------// // find the best indices int *bestIndices = findBestCandidates(nCandidates, results, nHiPeriodInSamples - nLowPeriodInSamples - 1); //note findBestCandidates modifies parameter // convert back to Hz double *res = new double[nCandidates]; for (int i=0; i < nCandidates;i++) res[i] = periodInSamplesToHz(bestIndices[i]+nLowPeriodInSamples, 2048); double pitch2 = res[0]; free(res); free(results); return pitch2; } /// Finds n "best" values from an array. Returns the indices of the best parts. /// (One way to do this would be to sort the array, but that could take too long. /// Warning: Changes the contents of the array!!! Do not use result array afterwards. int* findBestCandidates(int n, double* inputs,int length) { //int length = inputs.Length; if (length < n) printf("Length of inputs is not long enough."); int *res = new int[n]; double minValue = 0; for (int c = 0; c < n; c++) { // find the highest. double fBestValue = minValue; int nBestIndex = -1; for (int i = 0; i < length; i++) { if (inputs[i] > fBestValue) { nBestIndex = i; fBestValue = inputs[i]; } } // record this highest value res[c] = nBestIndex; // now blank out that index. if(nBestIndex!=-1) inputs[nBestIndex] = minValue; } return res; } int hzToPeriodInSamples(double hz, int sampleRate) { return (int)(1 / (hz / (double)sampleRate)); } double periodInSamplesToHz(int period, int sampleRate) { return 1 / (period / (double)sampleRate); } Thanks, Niall. Edit: Changed the code to implement a high pass filter with a cutoff of 30hz (from What Are High-Pass and Low-Pass Filters?, can anyone tell me how to convert the low-pass filter using convolution to a high-pass one?) but it's still returning random results. Plugging it into a VST host and using VST plugins to compare spectrums isn't an option to me unfortunately.

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  • Recommended Clang command line options

    - by frou
    The Manual for Clang seems to be work in progress, so could you help me formulate the definitive command line options for compiling ANSI-C (AKA C89, C90) with maximum strictness and relevant/helpful warnings? Clang is a compiler front end for the C, C++, and Objective-C programming languages. It uses the Low Level Virtual Machine (LLVM) as its back end. It is still under development. Its goal is to offer a replacement to the GNU Compiler Collection (GCC)

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  • Where is the VM in LLVM?

    - by anon
    Note: marked as community wiki. Where is the Low Level Virtual Machine in LLVM? I see that we have llvm-g++ and c-lang, but to me, a LLVM is something almost like Valgrind of a simulator, where instructions are executed on it, and I can write programs to instrument the running code / interrupt when certain conditions happen / etc ... Where are the tools like this built on LLVM? Thanks!

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  • Great UIKit/Objective-C one-Liners

    - by Nissan Fan
    New to Objective-C iPhone/iPod touch/iPad development, but I'm starting to discover lots of power in one-liners of code such as this: [UIApplication sharedApplication].applicationIconBadgeNumber = 10; Which will display that distinctive red notification badge on your app iphone with the number 10. Please share you favorite one-liners in Objective-C for the iPhone/iPod touch/iPad here.

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  • The C++ Standard: Book Recommendation.

    - by Nawaz
    I'm planning to buy this book: The C++ Standard: Incorporating Technical Corrigendum No. 1 http://www.flipkart.com/standard-british-standards-institution-incorporating-book-0470846747 Since it's cost is too much for me (being an Indian we've the habit of buying only low-price edition books :D), I want to make sure if this is the correct edition/version of the Standard. So I need some good advice if I should go for it, or there is better option for me which I'm unaware of. PS: I want to buy hard copy, not PDF.

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  • Why are there so many data centres in Texas?

    - by jklp
    I've been searching for online hosting recently and have noticed a high concentration of hosting providers in Texas. Just wondering why this is? It couldn't be possibly be because of temperature (I don't think Texas is a particularly cool place to be) or maybe power is cheaper in Texas vs the rest of the States? Or maybe it's just there are laws in place which give hosting providers tax breaks? Would be very interested to find out.

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  • how good is java's UUID.randomUUID?

    - by Alvin
    I know randomized UUID have very very very low probability for collision in theory, but I am wondering, in practice, how good is java 5's randonUUID in terms of not having collision? Does anybody have any experience to share?

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  • Hash Map Usage and Idea

    - by Anand
    Hi, I have been working in Java for the last 6 months and have been using Hash Maps What is the basic idea of a Hash Map ? I am using it as it easy for me to store so much data with direct key references rather than having to iterate through an arraylist ? Where is the power of Hash Map seen ? What is the scientific idea behind this data structure ?

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  • Erlang programming exercises

    - by valya
    I'm learning Erlang. I've moved from Haskell so I don't want to and have to learn functional programming. But Erlang is quite specific because of the microprocesses. So, can you give me some examples which will be simple to test and measure and use all the power of Erlang?

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  • handling NSStream events when using EASession in MonoTouch

    - by scotru
    Does anyone have an example of how to handle read and write NSStream events in Monotouch when working with accessories via EASession? It looks like there isn't a strongly typed delegate for this and I'm having trouble figuring out what selectors I need to handle on the delegates of my InputStream and OutputStream and what I actually need to do with each selector in order to properly fill and empty the buffers belonging to the EASession object. Basically, I'm trying to port Apple's EADemo app to Monotouch right now. Here's the Objective-C source that I think is relevant to this problem: / / asynchronous NSStream handleEvent method - (void)stream:(NSStream *)aStream handleEvent:(NSStreamEvent)eventCode { switch (eventCode) { case NSStreamEventNone: break; case NSStreamEventOpenCompleted: break; case NSStreamEventHasBytesAvailable: [self _readData]; break; case NSStreamEventHasSpaceAvailable: [self _writeData]; break; case NSStreamEventErrorOccurred: break; case NSStreamEventEndEncountered: break; default: break; } } / low level write method - write data to the accessory while there is space available and data to write - (void)_writeData { while (([[_session outputStream] hasSpaceAvailable]) && ([_writeData length] > 0)) { NSInteger bytesWritten = [[_session outputStream] write:[_writeData bytes] maxLength:[_writeData length]]; if (bytesWritten == -1) { NSLog(@"write error"); break; } else if (bytesWritten > 0) { [_writeData replaceBytesInRange:NSMakeRange(0, bytesWritten) withBytes:NULL length:0]; } } } // low level read method - read data while there is data and space available in the input buffer - (void)_readData { #define EAD_INPUT_BUFFER_SIZE 128 uint8_t buf[EAD_INPUT_BUFFER_SIZE]; while ([[_session inputStream] hasBytesAvailable]) { NSInteger bytesRead = [[_session inputStream] read:buf maxLength:EAD_INPUT_BUFFER_SIZE]; if (_readData == nil) { _readData = [[NSMutableData alloc] init]; } [_readData appendBytes:(void *)buf length:bytesRead]; //NSLog(@"read %d bytes from input stream", bytesRead); } [[NSNotificationCenter defaultCenter] postNotificationName:EADSessionDataReceivedNotification object:self userInfo:nil]; } I'd also appreciate any architectural recommendations on how to best implement this in monotouch. For example, in the Objective C implementation these functions are not contained in any class--but in Monotouch would it make sense to make them members of my

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  • What is holding up HD video conferencing on the web?

    - by Tristan
    What exactly is holding up real-time HD video conferencing on the web? Live, low-latency, video has lots of great applications beyond video chat: for instance, virtual desktops / vnc, remote control of applications, and server-side visualization. So what exactly are the technical barriers that remain? Existing video and remote desktop applications show latency problems are overrated for many applications. Bandwidth for many users now can easily stream 720p and even 1080p. Top-end video conferencing demos already do 1080p

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  • Bitwise Operations -- Arithmetic Operations..

    - by RBA
    Hi, Can you please explain the below lines, with some good examples. A left arithmetic shift by n is equivalent to multiplying by 2n (provided the value does not overflow), while a right arithmetic shift by n of a two's complement value is equivalent to dividing by 2n(2 to the power n) and rounding toward negative infinity. If the binary number is treated as ones' complement, then the same right-shift operation results in division by 2n and rounding toward zero. Thankx..

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  • Display arbitrary size 2d image in opengl

    - by Martin Beckett
    I need to display 2d images in opengl using textures. The image dimensions are not necessarily powers of 2. I thought of creating a larger texture and restricting the display to the part I was using but the image data will be shared with openCV so I don't want to copy data a pixel at a time into a larger texture. EDIT - it turns out that even the simplest Intel on board graphics under Windows supports none-power-of-2 textures.

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  • ClientRoleProvider and role caching...

    - by Kieron
    Hi, Is it possible to disable to the role caching when using the ClientRoleProvider? The application in question is a console application... I've tried setting 'cacheRolesInCookie' to false (I know it's a console app, but I was running low on ideas!) - but it had no affect.

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  • How to write "Hello World" Program for MediaTek SDK?

    - by Mediatek Beginner
    Hi Friends, I know these days number of mobile handsets are increasing and Vendors are trying to produce low cost handsets and some how I got to know that MediaTek SDK is the right one to write program for these kind of handsets. Is there any one who knows which IDE should I use to write programs for these kind of handsets? Is there any source code and sample available? I know that Fly, Karbonn, Lava Mobiles are Mediatek sdk based. Please Help Me. Regards, Mediatek Beginner

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  • Prevent lock of windows detecting user idle time

    - by Zimelemon
    I work in a Windows Terminal Server enviroment where if you left the computer for a while, windows lock the session and terminal is power off. What i need is the code needed to send a message to Windows for it to believe the user is in front of the PC (mouse or keyboard activity). Thanks in advance

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  • Is there any web service for getting tidal information?

    - by thor
    Has anyone come across a web service or plugin/code/calculation for getting information on tides - namely high and low tide times? I only need this information for one location (outwith the US) but I need it on an ongoing basis so a web service that I can hit once a day or something would be ideal.

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