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  • C/C++ - Convert 24-bit signed integer to float

    - by e-t172
    I'm programming in C++. I need to convert a 24-bit signed integer (stored in a 3-byte array) to float (normalizing to [-1.0,1.0]). The platform is MSVC++ on x86 (which means the input is little-endian). I tried this: float convert(const unsigned char* src) { int i = src[2]; i = (i << 8) | src[1]; i = (i << 8) | src[0]; const float Q = 2.0 / ((1 << 24) - 1.0); return (i + 0.5) * Q; } I'm not entirely sure, but it seems the results I'm getting from this code are incorrect. So, is my code wrong and if so, why?

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  • How do calculators work with precision?

    - by zoul
    Hello! I wonder how calculators work with precision. For example the value of sin(M_PI) is not exactly zero when computed in double precision: #include <math.h> #include <stdio.h> int main() { double x = sin(M_PI); printf("%.20f\n", x); // 0.00000000000000012246 return 0; } Now I would certainly want to print zero when user enters sin(p). I can easily round somewhere on 1e–15 to make this particular case work, but that’s a hack, not a solution. When I start to round like this and the user enters something like 1e–20, they get a zero back (because of the rounding). The same thing happens when the user enters 1/10 and hits the = key repeatedly — when he reaches the rounding treshold, he gets zero. And yet some calculators return plain zero for sin(p) and at the same time they can work with expressions such as (1e–20)/10 comfortably. Where’s the trick?

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  • Typecasting a floating value or using the math.h floor* functions?

    - by nobody
    Hi, I am coding up an implementation of Interpolation Search in C. The question is actually rather simple, I need to use the floating operations to do linear interpolation to find the correct index which will eventually be an integer result. In particular my probe index is: t = i + floor((((k-low)/(high-low)) * (j-i))); where, i,j,k,t are unsigned ints, and high,low are doubles. Would this be equivalent to: t = i + (unsigned int)(((k-low)/(high-low)) * (j-i)); Is there any reason I would actually want to use math.h floor* functions over just a simple (int) typecast?

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  • How to mark empty in a single element in a float array

    - by Vineeth Mohan
    I have a large float (primitive) array and not every element in the array is filled. How can i mark a particular element as EMPTY. I understand this can be achieved by some special symbols but still i would like to know the standard way. Even if i am using some special symbol , how will i handle a situation where the actual data item is the value of special symbol. In short my question is how to implement the NULL feature in a primitive type array in java. PS - The reason why i am not using Float object is to achieve a high memory and speed performance. Thanks Vineeth

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  • How to compare two floating-point values in shell script

    - by Reem
    I had to do a division in shell script and the best way was: result1=`echo "scale=3; ($var1 / $total) * 100"| bc -l` result2=`echo "scale=3; ($var2 / $total) * 100"| bc -l` but I want to compare the values of $result1 and $result2 Using if test $result1 -lt $result2 or if [ $result1 -gt $result2 ] didn't work :( Any idea how to do that?

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  • Dont know how to stop element in certain point

    - by user713190
    Im beginner and im experimenting on a website with fixed and relative postions, what i want to do is to stop bottom part when the two bottom lines(div .top_divider_line) touches nav menu(div .top_holder) here is the preview from site where im stuck. http://elexoj.com/test/ I think making it with jquery will be lot easier but i've no idea how to do it, i'll really appreciate your help. Thank You!

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  • Why might different computers calculate different arithmetic results in VB.NET?

    - by Eyal
    I have some software written in VB.NET that performs a lot of calculations, mostly extracting jpegs to bitmaps and computing calculations on the pixels like convolutions and matrix multiplication. Different computers are giving me different results despite having identical inputs. What might be the reason? Edit: I can't provide the algorithm because it's proprietary but I can provide all the relevant operations: ULong \ ULong (Turuncating division) Bitmap.Load("filename.bmp') (Load a bitmap into memory) Bitmap.GetPixel(Integer, Integer) (Get a pixel's brightness) Double + Double Double * Double Math.Sqrt(Double) Math.PI Math.Cos(Double) ULong - ULong ULong * ULong ULong << ULong List.OrderBy(Of Double)(Func) Hmm... Is it possible that OrderBy is using a non-stable QuickSort and that QuickSort is using a random pivot? Edit: Just tested, nope. The sort is stable.

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  • Swap bits in c++ for a double

    - by hidayat
    Im trying to change from big endian to little endian on a double. One way to go is to use double val, tmp = 5.55; ((unsigned int *)&val)[0] = ntohl(((unsigned int *)&tmp)[1]); ((unsigned int *)&val)[1] = ntohl(((unsigned int *)&tmp)[0]); But then I get a warning: "dereferencing type-punned pointer will break strict-aliasing rules" and I dont want to turn this warning off. Another way to go is: #define ntohll(x) ( ( (uint64_t)(ntohl( (uint32_t)((x << 32) >> 32) )) << 32) | ntohl( ((uint32_t)(x >> 32)) ) ) val = (double)bswap_64(unsigned long long(tmp)); //or val = (double)ntohll(unsigned long long(tmp)); But then a lose the decimals. Anyone know a good way to swap the bits on a double without using a for loop?

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  • Why is my number being rounded incorrectly?

    - by izb
    This feels like the kind of code that only fails in-situ, but I will attempt to adapt it into a code snippet that represents what I'm seeing. float f = myFloat * myConstInt; /* Where myFloat==13.45, and myConstInt==20 */ int i = (int)f; int i2 = (int)(myFloat * myConstInt); After stepping through the code, i==269, and i2==268. What's going on here to account for the difference?

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  • Mercurial: Diff current source vs source at point in time

    - by Marcus
    I know how to view all changes in a changeset.. But let's say you update your source, you do a pull and you get 3 new changesets. How can you compare the current state of the remote repository (with the 3 changesets checked in) vs. the current source (on your local machine)? I'd like to do this using the visual diff tool which I currently have configured (Examdiff or Kdiff3).

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  • Element point map for html5 canvas element, need algorithm

    - by Artiom Chilaru
    I'm currently working on a pure html 5 canvas implementation of the "flying tag cloud sphere", which many of you have undoubtedly seen as a flash object in some pages. The tags are drawn fine, and the performance is satisfactory, but there's one thing in the canvas element that's kind of breaking this idea: you can't identify the objects that you've drawn on a canvas, as it's just a simple flat "image".. What I have to do in this case is catch the click event, and try to "guess" which element was clicked. So I have to have some kind of matrix, which stores a link to a tag object for each pixel on the canvas, AND I have to update this matrix on every redraw. Now this sounds incredibly inefficient, and before I even start trying to implement this, I want to ask the community - is there some "well known" algorithm that would help me in this case? Or maybe I'm just missing something, and the answer is right behind the corner? :)

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  • PHP math gets crazy, need explanation, my brain is melting

    - by derei
    I know that playing with php float can give strange results if you try to add "goats + apples", but please take a look to the following case: $val = 1232.81; $p1 = 1217.16; $p2 = 15.65; $sum = $p1 + $p2; $dif = $val - $sum; echo $dif; It will give you -2.2737367544323E-13 ... yeah, ALMOST zero, but then why it doesn't say 0 ? This freaks me out big time. Please, I need some valid explanation.

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  • POS for .NET Known Service Objects

    - by Oliver S
    Hi, I was wondering if anyone knew where I could find a list of LineDisplays, CashDrawers, Printers, that work well with POS for .NET. I want to get around creating my own service objects for potential devices that I might by which are not supported. Thanks.

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  • CSS3 new features...whats the point?

    - by benhowdle89
    I've been reading a lot of ways recently of how to avoid having to use Photoshop for things like gradients and shadows on buttons, when you can use CSS3 Box Shadow for such features. Now this is great, but obviously legacy browsers and most IE browsers don't yet implement CSS3 features, so my question is, why save yourself extra work in Photoshop when you can use CSS3 but then HAVE to use Photoshop for other browsers to see the desired effects? Isn't that just extra work?

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  • what is the point of return in ruby?

    - by Sam
    What is the difference between return and just putting a variable such as the following: return def write_code(number_of_errors) if number_of_errors > 1 mood = "WTF" else mood = "No Problem" end mood end no return def write_code(number_of_errors) if number_of_errors > 1 mood = "WTF" else mood = puts "No Problem" end return mood end

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  • Handling input from a keyboard wedge

    - by JDibble
    Following on from the question asked by Mykroft Best way to handle input from a keyboard “wedge” http://stackoverflow.com/questions/42437/best-way-to-handle-input-from-a-keyboard-wedge. I need to write a class that intercepts key strokes, if the input is determined to be from the keyboard wedge (as described in the above post) the data will be directed to POS classes to handle, otherwise they keystrokes must be passed on to be handled in windows in the normal manner. This raises two questions How can I intercept key strokes when not in a WinForm. How can I pass on the keypresses to windows. Thanks JDibble

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  • Float Conversion Issue

    - by user1407570
    I have an issue after converted a float from a string, the result of my operation is null The NSLogs give the right value but vitesseMoyenne is equal to null -(void)setVitesseMoyenne:(float)uneDistanceTotale:(NSString*)unTempsTotal { //float tempEnFloat = [unTempsTotal floatValue]; NSLog(@"%@",unTempsTotal); float calculVitesseMoyenne = uneDistanceTotale / [unTempsTotal floatValue]; NSLog(@"%f",calculVitesseMoyenne); vitesseMoyenne = [NSString stringWithFormat:@"%f", calculVitesseMoyenne]; } Can you see what is wrong ?

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  • Is it possible to read Fortran formatted data in Python?

    - by Werner
    I get output files from very old Fortran programs, which look like: 0.81667E+00 -0.12650E+01 -0.69389E-03 0.94381E+00 -0.11985E+01 -0.11502E+00 0.96064E+00 -0.11333E+01 -0.17616E+00 0.10202E+01 -0.12435E+01 -0.93917E-01 0.10026E+01 -0.10904E+01 -0.15108E+00 0.90516E+00 -0.11030E+01 -0.19139E+00 0.98624E+00 -0.11598E+01 -0.22970E+00 Is it possible to read this in Python and convert the numbers to "normal" floats?

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  • Create all directories up to a point?

    - by Stefan Kendall
    I need to be able to build all directories up to and including the directory specified by my File object. For example, suppose I have something like this: File file = new File( "/var/a/b/c/d/" ); But only /var/ exists. I need a method that builds up to d, and I was wondering if there was a method in a java io library somewhere that does this already.

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  • MySQL float values jumping around on insert?

    - by dubayou
    So i have a SQL table setup as such CREATE TABLE IF NOT EXISTS `points` ( `id` int(11) NOT NULL auto_increment, `lat` float(10,6) NOT NULL, `lng` float(10,6) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM; And im inserting stuff like INSERT INTO `points` (`lat`, `lng`) VALUES ('89.123456','-12.123456'); Gives me a row with lat and lng being 89.123459 and -12.123455 Whats up?

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