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  • sin v/s sinf fucntion in C

    - by user319873
    Hi Guys, I am trying to use sinf function in my C Program and it does give me undefined reference under MSVC 6.0 but sin works fine. This make me curious to find the difference between sin and sinf. What is the logical difference between sin and sinf(). How can I implement my own sinf functionality?

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  • How do I find hash value of a 3D vector ?

    - by brainydexter
    I am trying to perform broad-phase collision detection with a fixed-grid size approach. Thus, for each entity's position: (x,y,z) (each of type float), I need to find which cell does the entity lie in. I then intend to store all the cells in a hash-table and then iterate through to report (if any) collisions. So, here is what I am doing: Grid-cell's position: (int type) (Gx, Gy, Gz) = (x / M, y / M, z / M) where M is the size of the grid. Once, I have a cell, I'd like to add it to a hash-table with its key being a unique hash based on (Gx, Gy, Gz) and the value being the cell itself. Now, I cannot think of a good hash function and I need some help with that. Can someone please suggest me a good hash function? Thanks

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  • Inaccurate Logarithm in Python

    - by Avihu Turzion
    I work daily with Python 2.4 at my company. I used the versatile logarithm function 'log' from the standard math library, and when I entered log(2**31, 2) it returned 31.000000000000004, which struck me as a bit odd. I did the same thing with other powers of 2, and it worked perfectly. I ran 'log10(2**31) / log10(2)' and I got a round 31.0 I tried running the same original function in Python 3.0.1, assuming that it was fixed in a more advanced version. Why does this happen? Is it possible that there are some inaccuracies in mathematical functions in Python?

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  • what is the point of escaping quotation marks in php

    - by Jacksta
    Here is a validation script from a book I am learning, Why is escaping the quotation marks necassery? e.g. <option value=\"char\">char</option> <?php //validate important input if ((!$_POST[table_name]) || (!$_POST[num_fields])) { header( "location: show_createtable.html"); exit; } //begin creating form for display $form_block = " <form action=\"do_createtable.php\" method=\"post\"> <input name=\"table_name\" type=\"hidden\" value=\"$_POST[table_name]\"> <table cellspacing=\"5\" cellpadding=\"5\"> <tr> <th>Field Name</th><th>Field Type</th><th>Table Length</th> </tr>"; //count from 0 until you reach the number fo fields for ($i = 0; $i <$_POST[num_fields]; $i++) { $form_block .=" <tr> <td align=center><input type=\"texr\" name=\"field name[]\" size=\"30\"></td> <td align=center> <select name=\"field_type[]\"> <option value=\"char\">char</option> <option value=\"date\">date</option> <option value=\"float\">float</option> <option value=\"int\">int</option> <option value=\"text\">text</option> <option value=\"varchar\">varchar</option> </select> </td> <td align=center><input type=\"text\" name=\"field_length[]\" size=\"5\"> </td> </tr>"; } //finish up the form $form_block .= " <tr> <td align=center colspan=3><input type =\"submit\" value=\"create table\"> </td> </tr> </table> </form>"; ?> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Create a database table: Step 2</title> </head> <body> <h1>defnie fields for <? echo "$_POST[table_name]"; ?> </h1> <? echo "$form_block"; ?> </body> </html>

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  • What is the point of CSS collapsing margins?

    - by Tom
    The CSS2 box model tells us that adjoining margins collapse. I find it quite annoying, being the source of many design bugs. I hope that by understanding the purpose of collapsing margins, I will understand when to use them and how to avoid them when they are not needed. What is the purpose of this feature?

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  • x86-64 long double precision

    - by aaa
    hello. What is the actual precision of long double on Intel 64-bit platforms? is it 80 bits padded to 128 or actual 128 bit? if former, besides going gmp, is there another option to achieve true 128 precision?

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  • Make an URL point to google maps app on Nokia (symbian)

    - by tvgemert
    Hi, The iPhone has a functionality that when a google maps URL is typed into (or linked) the mobile browser it will open the Google Maps app instead of displaying it in the mobile browser. Now I'm wondering if that same functionality exists for say a Nokia (Symbian) phone? Is there a way to set up the link to open the Google maps app on the Symbian phone?

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  • Calculate and display distance between userlocation and known point in Table View

    - by Claudio
    Hi, I have a table view with a list of hotel, and i want put in cell.detailTextLabel.text the distance beetween userlocation and hotel. How can obtain the coordinates of userlocation? I see on web that i need to use CLLocationManager but i don't understand how and where implement in my table view. Then,to get the distance,i do a "getDistancefrom" between userLocation and the coordinates of the hotel ? Thanks

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  • How to calculate point along a curve?

    - by Nicros
    I am writing a custom animation for wpf and as a non math guy I have a couple questions... If I am given two Point3D's, the From and To, and assuming the origin is at 0,0,0 how do I calculate a curve between the two points? And once I have the curve 'plotted' and I know its length (how to do that too?) how can I calculate the x,y,z coords at some given distance along the line? Thanks!

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  • Reducing decimal places in Delphi

    - by Hendriksen123
    I am storing a list of numbers (as Double) in a text file, then reading them out again. When I read them out of the text file however, the numbers are placed into the text box as 1.59993499 for example, instead of 1.6. AssignFile(Pipe, 'EconomicData.data'); Reset(Pipe); For i := 1 to 15 Do ReadLn(Pipe, SavedValue[i]); CloseFile(Pipe); Edit1.Text := FloatToStr(SavedValue[1]); The text in Edit1.text, from the code above, would be 1.59999... instead of the 1.6 in the text file. How can i make it so the text box displays the original value (1.6)?

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  • Faster float to int conversion in Python

    - by culebrón
    Here's a piece of code that takes most time in my program, according to timeit statistics. It's a dirty function to convert floats in [-1.0, 1.0] interval into unsigned integer [0, 2**32]. How can I accelerate floatToInt? piece = [] rng = range(32) for i in rng: piece.append(1.0/2**i) def floatToInt(x): n = x + 1.0 res = 0 for i in rng: if n >= piece[i]: res += 2**(31-i) n -= piece[i] return res

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  • URL rewriting to a common end point

    - by sunil
    I want to create an asp.net white-label site http://whitelabel.com, that could be styled for each of our clients according to their specific needs. So for example, client abc would see the site in their corporate colours and be accessed through their specific url http://abc.com. Likewise client xyz would see the site in their own styling and url http://xyz.com. Typing either url, in effect, takes the user to http://whitelabel.com where the styling is applied, and the client's url structure is retained. I was thinking of URL rewriting using URLRewriter.Net (http://urlrewriter.net/), or similar, mapping the incoming address to a client id and applying the theme accordingly. So, a url rewrite rule may be something like <rewrite url="http//abc.com/(.+)" to="~/$1?id=1" /> <rewrite url="http//xyz.com/(.+)" to="~/$1?id=2" /> I could then read the id, map it to the client, and with a bit of jiggery-pokery, apply the correct theme. I was wondering if: this is the right approach ? I've overlooked something ? there is a better way to do this ? Any suggestions would be appreciated.

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  • what is the point of heterogenous arrays?

    - by aharon
    I know that more-dynamic-than-Java languages, like Python and Ruby, often allow you to place objects of mixed types in arrays, like so: ["hello", 120, ["world"]] What I don't understand is why you would ever use a feature like this. If I want to store heterogenous data in Java, I'll usually create an object for it. For example, say a User has int ID and String name. While I see that in Python/Ruby/PHP you could do something like this: [["John Smith", 000], ["Smith John", 001], ...] this seems a bit less safe/OO than creating a class User with attributes ID and name and then having your array: [<User: name="John Smith", id=000>, <User: name="Smith John", id=001>, ...] where those <User ...> things represent User objects. Is there reason to use the former over the latter in languages that support it? Or is there some bigger reason to use heterogenous arrays? N.B. I am not talking about arrays that include different objects that all implement the same interface or inherit from the same parent, e.g.: class Square extends Shape class Triangle extends Shape [new Square(), new Triangle()] because that is, to the programmer at least, still a homogenous array as you'll be doing the same thing with each shape (e.g., calling the draw() method), only the methods commonly defined between the two.

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  • AVPlayer seeking to a different point after app resume

    - by CGuess
    I have an AVPlayer, the video in it is ~2 seconds long. After the video plays, if the app goes to the background and reenters the foreground I need the video to still be shown exactly as it was when the app was exited. The AVPlayer sticks around just fine, however when I reenter the app from the background the video appears to be seeked to the middle of the video. However, if I just play the video, it starts from the beginning, so it doesn't seem like it actually seeked and is just showing a preview image. I've tried to auto-seek the video to the end on relaunch but nothing happens . Nothing I can figure out or find in the docs would describe this behavior. Any tips on having the video launch either at the beginning or end?

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  • negative precision values in ostream

    - by daz-fuller
    This is more of a question of curiosity but does anyone know how negative precision values are handled in C++? For example: double pi = 3.14159265; cout.precision(-10); cout.setf(ios::fixed, ios::floatfield); cout << pi << endl; I've tried this out and using GCC and it seems that the precision value is ignored but I was curious if there is some official line on what happens in this situation.

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  • How to make gcc on SUN calculate floating points the same way as in Linux

    - by Marina
    I have a project where I have to perform some mathematics calculations with double variables. The problem is that I get different results on SUN Solaris 9 and Linux. There are a lot of ways (explained here and other forums) how to make Linux work as Sun, but not the other way around. I cannot touch the Linux code, so it is only SUN I can change. Is there any way to make SUN to behave as Linux? The code I run(compile with gcc on both systems): int hash_func(char *long_id) { double product, lnum, gold; while (*long_id) lnum = lnum * 10.0 + (*long_id++ - '0'); printf("lnum => %20.20f\n", lnum); lnum = lnum * 10.0E-8; printf("lnum => %20.20f\n", lnum); gold = 0.6125423371582974; product = lnum * gold; printf("product => %20.20f\n", product); ... } if the input is 339886769243483 the output in Linux: lnum => 339886769243**483**.00000000000000000000 lnum => 33988676.9243**4829473495483398** product => 20819503.600158**59827399253845** When on SUN: lnum => 339886769243483.00000000000000000000 lnum => 33988676.92434830218553543091 product = 20819503.600158**60199928283691** Note: The result is not always different, moreover most of the times it is the same. Just 10 15-digit numbers out of 60000 have this problem. Please help!!!

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  • Collision point of 2 curves in a 3d-room

    - by Frank
    Hello, i am programming a small game for quite some time. We started coding a small FPS-Shooter inside of a project at school to get a bit experience using directX. I dont know why, but i couldnt stop the project and started programming at home aswell. At the moment i am trying to create some small AI. Of cause thats definatlly not easy, but thats my personal goal anyways. The topic could prolly fill multiple books hehe. I've got the walking part of my bots done so far. They walk along a scriped path. I am not working on the "aiming" of the bots. While programming that i hit on some math problem i couldnt solve yet. I hope of your input on this to help me get further. Concepts, ideas and everything else are highly appreciated. Problem: Calculate the position (D3DXVECTOR3) where the curve of the projectile (depends on gravity, speed), hit the curved of the enemys walking path (depends on speed). We assume that the enemy walks in a constant line. Known variables: float projectilSpeed = 2000 m/s //speed of the projectile per second float gravitation = 9.81 m/s^2 //of cause the gravity lol D3DXVECTOR3 targetPosition //position of the target stored in a vector (x,y,z) D3DXVECTOR3 projectilePosition //position of the projectile D3DXVECTOR3 targetSpeed //stores the change of the targets position in the last second Variabledefinition ProjectilePosition at time of collision = ProjectilePos_t TargetPosition at time of collision = TargetPos_t ProjectilePosition at time 0, now = ProjectilePos_0 TargetPosition at time 0, now = TargetPos_0 Time to impact = t Aim-angle = theta My try: Found a formular to calculate "drop" (Drop of the projectile based on the gravity) on Wikipedia: float drop = 0.5f * gravity * t * t The speed of the projectile has a horizontal and a vertical part.. Found a formular for that on wikipedia aswell: ProjectilVelocity.x = projectilSpeed * cos(theta) ProjectilVelocity.y = projectilSpeed * sin(theta) So i would assume this is true for the projectile curve: ProjectilePos_t.x = ProjectilePos_0.x + ProjectileSpeed * t ProjectilePos_t.y = ProjectilePos_0.y + ProjectileSpeed * t + 0.5f * gravity * t * t ProjectilePos_t.z = ProjectilePos_0.z + ProjectileSpeed * t The target walk with a constant speed, so we can determine his curve by this: TargetPos_t = TargetPos_0 + TargetSpeed * D3DXVECTOR3(t, t, t) Now i dont know how to continue. I have to solve it somehow to get a hold on the time to impact somehow. As a basic formular i could use: float time = distanz / projectileSpeed But that wouldnt be truly correct as it would assume a linear "Trajectory". We just find this behaivor when using a rocket. I hope i was able to explain the problem as much as possible. If there are questions left, feel free to ask me! Greets from germany, Frank

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  • Can bad stuff happen when dividing 1/a very small float?

    - by Jeremybub
    If I want to check that positive float A is less than the inverse square of another positive float B (in C99), could something go wrong if B is very small? I could imagine checking it like if(A<1/(B*B)) but if B is small enough, would this possibly result in infinity? If that were to happen, would the code still work correctly in all situations? in a similar vein, I might do if(1/A>B*B) Which might be slightly better because B*B might be zero if B is small (is this true?) Finally, a solution that I can't imagine being wrong is if(sqrt(1/A)>B) Which I don't think would ever result in zero division, but still might be problematic if A is close to zero. So basically, my questions are Can 1/X ever be infinity if X is greater than zero (but small)? Can X*X ever be zero if X is greater than zero? Will comparisons with infinity work the way I would expect them to?

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