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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 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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  • 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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  • Problem using the find function in MATLAB

    - by Peter Etchells
    I have two arrays of data that I'm trying to amalgamate. One contains actual latencies from an experiment in the first column (e.g. 0.345, 0.455... never more than 3 decimal places), along with other data from that experiment. The other contains what is effectively a 'look up' list of latencies ranging from 0.001 to 0.500 in 0.001 increments, along with other pieces of data. Both data sets are X-by-Y doubles. What I'm trying to do is something like... for i = 1:length(actual_latency) row = find(predicted_data(:,1) == actual_latency(i)) full_set(i,1:4) = [actual_latency(i) other_info(i) predicted_info(row,2) ... predicted_info(row,3)]; end ...in order to find the relevant row in predicted_data where the look up latency corresponds to the actual latency. I then use this to created an amalgamated data set, full_set. I figured this would be really simple, but the find function keeps failing by throwing up an empty matrix when looking for an actual latency that I know is in predicted_data(:,1) (as I've double-checked during debugging). Moreover, if I replace find with a for loop to do the same job, I get a similar error. It doesn't appear to be systematic - using different participant data sets throws it up in different places. Furthermore, during debugging mode, if I use find to try and find a hard-coded value of actual_latency, it doesn't always work. Sometimes yes, sometimes no. I'm really scratching my head over this, so if anyone has any ideas about what might be going on, I'd be really grateful.

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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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  • Doing arithmetic with up to two decimal places in Python?

    - by user248237
    I have two floats in Python that I'd like to subtract, i.e. v1 = float(value1) v2 = float(value2) diff = v1 - v2 I want "diff" to be computed up to two decimal places, that is compute it using %.2f of v1 and %.2f of v2. How can I do this? I know how to print v1 and v2 up to two decimals, but not how to do arithmetic like that. The particular issue I am trying to avoid is this. Suppose that: v1 = 0.982769777778 v2 = 0.985980444444 diff = v1 - v2 and then I print to file the following: myfile.write("%.2f\t%.2f\t%.2f\n" %(v1, v2, diff)) then I will get the output: 0.98 0.99 0.00, suggesting that there's no difference between v1 and v2, even though the printed result suggests there's a 0.01 difference. How can I get around this? thanks.

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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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  • strange results with /fp:fast

    - by martinus
    We have some code that looks like this: inline int calc_something(double x) { if (x > 0.0) { // do something return 1; } else { // do something else return 0; } } Unfortunately, when using the flag /fp:fast, we get calc_something(0)==1 so we are clearly taking the wrong code path. This only happens when we use the method at multiple points in our code with different parameters, so I think there is some fishy optimization going on here from the compiler (Microsoft Visual Studio 2008, SP1). Also, the above problem goes away when we change the interface to inline int calc_something(const double& x) { But I have no idea why this fixes the strange behaviour. Can anyone explane this behaviour? If I cannot understand what's going on we will have to remove the /fp:fastswitch, but this would make our application quite a bit slower.

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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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  • Why does ghci say that 1.1 + 1.1 + 1.1 > 3.3 is True?

    - by Frerich Raabe
    I've been going through a Haskell tutorial recently and noticed this behaviour when trying some simple Haskell expressions in the interactive ghci shell: Prelude> 1.1 + 1.1 == 2.2 True Prelude> 1.1 + 1.1 + 1.1 == 3.3 False Prelude> 1.1 + 1.1 + 1.1 > 3.3 True Prelude> 1.1 + 1.1 + 1.1 3.3000000000000003 Does anybody know why that is?

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  • How to make your website works on a projector?

    - by iyad al aqel
    I have a presentation tomorrow, and while I was trying to project my website using projector all the elements appeared mixed up. The problem is I used a software called "AXURE" to do the website. The HTML files produced by this software are crap. There's no one unified CSS file. The style is embedded for each element in the <div> tag and every element is positined by absolute pixels. How can make my website works on larger screens?

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  • Why does GLSL's arithmetic functions yield so different results on the iPad than on the simulator?

    - by cheeesus
    I'm currently chasing some bugs in my OpenGL ES 2.0 fragment shader code which is running on iOS devices. The code runs fine in the simulator, but on the iPad it has huge problems and some of the calculations yield vastly different results, I had for example 0.0 on the iPad and 4013.17 on the simulator, so I'm not talking about small differences which could be the result of some rounding errors. One of the things I noticed is that, on the iPad, float1 = pow(float2, 2.0); can yield results which are very different from the results of float1 = float2 * float2; Specifically, when using pow(x, 2.0) on a variable containing a larger negative number like -8, it seemed to return a value which satified the condition if (powResult <= 0.0). Also, the result of both operations (pow(x, 2.0) as well as x*x) yields different results in the simulator than on the iPad. Used floats are mediump, but I get the same stuff with highp. Is there a simple explanation for those differences? I'm narrowing the problem down, but it takes so much time, so maybe someone can help me here with a simple explanation.

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  • Can anyone explain this strange behaviour?

    - by partizan
    Hi, guys. Here is the example with comments: class Program { // first version of structure public struct D1 { public double d; public int f; } // during some changes in code then we got D2 from D1 // Field f type became double while it was int before public struct D2 { public double d; public double f; } static void Main(string[] args) { // Scenario with the first version D1 a = new D1(); D1 b = new D1(); a.f = b.f = 1; a.d = 0.0; b.d = -0.0; bool r1 = a.Equals(b); // gives true, all is ok // The same scenario with the new one D2 c = new D2(); D2 d = new D2(); c.f = d.f = 1; c.d = 0.0; d.d = -0.0; bool r2 = c.Equals(d); // false! this is not the expected result } } So, what do you think about this?

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  • Double multiplied by 100 and then cast to long is giving wrong value

    - by xyz
    I have the following code: Double i=17.31; long j=(long) (i*100); System.out.println(j); O/P : 1730 //Expected:1731 Double i=17.33; long j=(long) (i*100); System.out.println(j); O/P : 1732 //Expected:1733 Double i=17.32; long j=(long) (i*100); System.out.println(j); O/P : 1732 //Expected:1732{As expected} Double i=15.33; long j=(long) (i*100); System.out.println(j); O/P : 1533 //Expected:1533{as Expected} I have tried to Google but unable to find reason.I am sorry if the question is trivial.

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  • How to correctly and standardly compare floats?

    - by DIMEDROLL
    Every time I start a new project and when I need to compare some float or double variables I write the code like this one: if (fabs(prev.min[i] - cur->min[i]) < 0.000001 && fabs(prev.max[i] - cur->max[i]) < 0.000001) { continue; } Then I want to get rid of these magic variables 0.000001(and 0.00000000001 for double) and fabs, so I write an inline function and some defines: #define FLOAT_TOL 0.000001 So I wonder if there is any standard way of doing this? May be some standard header file? It would be also nice to have float and double limits(min and max values)

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  • Accordion "growing out" from its container - in IE7/8

    - by Richard Knop
    I think this problem is best explained by images. This is how my accordion looks: When you click on the small plus/minus icons the slides under each chapter will expand/collapse. However when the content in the accordion grows too tall, it grows out from its container. So if I click on more plus icons the accordion will look like this (not pretty): As you can see, the container is not growing taller together with the accordion and it does not look good. This problem only occurs in IE7 and IE8. It works in Firefox and Chrome. The HTML looks like this (simplified): <div id="content"> <div class="box2 rounded-corners"> <div class="chapters"> <h3><a href="/clientarea/view/archived-course/teid/133">Obsah</a></h3> <div id="accordion"> <ul> ... // accordion content - too long ... // accordion content - too long </ul> <div class="clear">&nbsp;</div> </div> <div class="clear">&nbsp;</div> </div> <div class="training-body"> ... // content to the right of the accordion </div> </div> </div> The CSS, again siplified: html, body { height: 100%; width: 100%; overflow: auto; } #content { background: white url('/images/background_middle.png') left top repeat-x; padding: 13px; min-height: 40em; height: auto !important; height: 40em; } /* this is the div with rounded corners */ #content .box2 { background: white; padding: 0 15px 15px; border: 1px solid #C5E3F8; position: relative; } /* left sidebar 98 #content div.chapters { float: left; width: 224px; } /* orange heading "OBSAH" */ #content div.chapters h3 { color: #ff6e19; text-transform: uppercase; font-size: .9em; text-align: center; padding-bottom: .5em; margin-top: 1em; margin-bottom: 0; } #content div.chapters h3 a { color: #ff6e19; } /* accordion */ #accordion { width: 226px; border-top: 1px solid #c5e3f8; } #accordion ul { padding-left: 0; margin-top: 0; margin-bottom: 0; margin-left: 0; } /* area to the right of the accordion */ #content div.training-body { float: left; padding-left: 0px; width: 748px; line-height: 1.3em; }

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  • Adding up fractions in PHP

    - by Gamemorize
    I would like to create a loop that keeps adding a set fraction, here in my example 1/3, and which later I can check against for matches with integer values. Obviously when php adds 1/3 + 1/3 + 1/3 the result is 0.9999999, so i thought I could use the occasional round to help me, but this isn't working either. The idea that I had would be that .333 + .333 becomes .666 and that if rounded that would become .667, then + .333 and the result is 1. However round only seems to work, for me, if the number of digits actually decreases. so round (0.666, 3) remains 0.666 <?php $denom = 3; $frac = 1/$denom; $frac = round($frac,3); $value = 0; $max =24; for($f = 1; $f <= $max; $f++){ echo "old value is now at ".$value.".<br/>"; $value = $value+$frac; echo "value is now at ".$value.".<br/>"; $value = round($value,3); echo "rounded value is now at ".$value.".<br/>"; $valueArray[$f] = $value; //and here for ease of testing.... if (($value==1)OR ($value==2)OR ($value==3)OR ($value==4)OR ($value==5)OR ($value==6)OR ($value==7)OR ($value==8)){ echo "match!<br/>"; }else{ echo "no match!<br/>"; } } ?> Am I going about this in a totally stupid way? Accuracy when the value is not an integer is not needed, just that it can == with integers.

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  • How to move value from the stack to ST(0)?

    - by George Edison
    I am having trouble believing the following code is the most efficient way to move a value from the stack to ST(0): .data var dd 4.2 tmp dd ? .code mov EAX, var push EAX ; top of stack now contains a value ; move it to ST(0) pop EAX mov tmp, EAX fld tmp Is the temporary variable really necessary? Further, is there an easier way to get a value from the stack to ST(0)?

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  • Function Returning Negative Value

    - by Geowil
    I still have not run it through enough tests however for some reason, using certain non-negative values, this function will sometimes pass back a negative value. I have done a lot of manual testing in calculator with different values but I have yet to have it display this same behavior. I was wondering if someone would take a look at see if I am missing something. float calcPop(int popRand1, int popRand2, int popRand3, float pERand, float pSRand) { return ((((((23000 * popRand1) * popRand2) * pERand) * pSRand) * popRand3) / 8); } The variables are all contain randomly generated values: popRand1: between 1 and 30 popRand2: between 10 and 30 popRand3: between 50 and 100 pSRand: between 1 and 1000 pERand: between 1.0f and 5500.0f which is then multiplied by 0.001f before being passed to the function above Edit: Alright so after following the execution a bit more closely it is not the fault of this function directly. It produces an infinitely positive float which then flips negative when I use this code later on: pPMax = (int)pPStore; pPStore is a float that holds popCalc's return. So the question now is, how do I stop the formula from doing this? Testing even with very high values in Calculator has never displayed this behavior. Is there something in how the compiler processes the order of operations that is causing this or are my values simply just going too high? If the later I could just increase the division to 16 I think.

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