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  • approximating log10[x^k0 + k1]

    - by Yale Zhang
    Greetings. I'm trying to approximate the function Log10[x^k0 + k1], where .21 < k0 < 21, 0 < k1 < ~2000, and x is integer < 2^14. k0 & k1 are constant. For practical purposes, you can assume k0 = 2.12, k1 = 2660. The desired accuracy is 5*10^-4 relative error. This function is virtually identical to Log[x], except near 0, where it differs a lot. I already have came up with a SIMD implementation that is ~1.15x faster than a simple lookup table, but would like to improve it if possible, which I think is very hard due to lack of efficient instructions. My SIMD implementation uses 16bit fixed point arithmetic to evaluate a 3rd degree polynomial (I use least squares fit). The polynomial uses different coefficients for different input ranges. There are 8 ranges, and range i spans (64)2^i to (64)2^(i + 1). The rational behind this is the derivatives of Log[x] drop rapidly with x, meaning a polynomial will fit it more accurately since polynomials are an exact fit for functions that have a derivative of 0 beyond a certain order. SIMD table lookups are done very efficiently with a single _mm_shuffle_epi8(). I use SSE's float to int conversion to get the exponent and significand used for the fixed point approximation. I also software pipelined the loop to get ~1.25x speedup, so further code optimizations are probably unlikely. What I'm asking is if there's a more efficient approximation at a higher level? For example: Can this function be decomposed into functions with a limited domain like log2((2^x) * significand) = x + log2(significand) hence eliminating the need to deal with different ranges (table lookups). The main problem I think is adding the k1 term kills all those nice log properties that we know and love, making it not possible. Or is it? Iterative method? don't think so because the Newton method for log[x] is already a complicated expression Exploiting locality of neighboring pixels? - if the range of the 8 inputs fall in the same approximation range, then I can look up a single coefficient, instead of looking up separate coefficients for each element. Thus, I can use this as a fast common case, and use a slower, general code path when it isn't. But for my data, the range needs to be ~2000 before this property hold 70% of the time, which doesn't seem to make this method competitive. Please, give me some opinion, especially if you're an applied mathematician, even if you say it can't be done. Thanks.

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  • How to prompt a streamed file for downloading in Java / Tomcat

    - by Clem
    Hello, I'm creating a java web application runing on a Tomcat server. One of the functions fill in a StringBuffer variable with data. At the end, I would like to propose the user to download the generated content packaged in a text file. This without having to store the file on the server. I've been searching for a code snippet but couldn't find anything corresponding ... I hope I've been clear enough on my problem. Thanks in advance,

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  • PostgreSQL function question

    - by maxxtack
    CREATE FUNCTION foo() RETURNS text LANGUAGE plperl AS $$ return 'foo'; $$; CREATE FUNCTION foobar() RETURNS text LANGUAGE plperl AS $$ return foo() . 'bar'; $$; I'm trying to compose results using multiple functions, but when i call foobar() i get an empty result.

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  • What is the best way to scale images in Java?

    - by Peter Kelley
    I have a web application written in Java (Spring, Hibernate/JPA, Struts2) where users can upload images and store them in the file system. I would like to scale those images so that they are of a consistent size for display on the site. What libraries or built in functions will offer the best results? I will consider the following criteria in making my decision (in this order): Free/Open Source (essential) Easy to implement Quality of results Performance Size of executable

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  • JQuery Attribute Manipulation

    - by TTCG
    When I search on the Internet about JQuery and I got the jquery cheat sheet. At there, I am very confused about how to use the following under which condition. Pls help me. [attribute|=val] [attribute*=val] [attribute~=val] [attribute$=val] [attribute=val] [attribute!=val] [attribute^=val] [attribute] [attribute1=val1] [attribute2=val2] What are the functions of these special character *, ~, $, !, ^? Thanks very much.

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  • Image Transformation on iPhone, how to?

    - by Horace Ho
    Since I cannot pre-render all the images in PNGs and real-time image transformation functions are required, namely: skew perspective (like the transform action found in Photoshop) Which API (CoreAnimation? OpenGL ES?) should I look into? Even better, is there any sample code around? Thanks!

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  • class vs structure c#

    - by Enriquev
    I'm doing course 3354 (Implementing System Types and Interfaces in the .NET Framework 2.0) and it is said that for simple classes, with members variables and functions, it is better to use a struct than a class because of overhead. I have never heard of such a thing, what is the validity of this claim?

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  • Add text to every line in text file using PowerShell

    - by Joshua
    I'd like to add characters to the end of every line of text in a .txt document. #Define Variables $a = c:\foobar.txt $b = get-content $a #Define Functions function append-text { foreach-Object { add "*" } } #Process Code $b | append-text Something like that. Essentially, load a given text file, add a "*" the the end of every single line of text in that text file, save and close.

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  • On OSX, how do I gradient fill a path stroke?

    - by Emiel
    Using the plethora of drawing functions in Cocoa or Quartz it's rather easy to draw paths, and fill them using a gradient. I can't seem to find an acceptable way however, to 'stroke'-draw a path with a line width of a few pixels and fill this stroke using a gradient. How is this done?

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  • mvc external javascript referencing problem

    - by user281180
    I recently asked this question but to my suprise, it worked fine for some time and now has stopped again! I have a javascript in my script and I have added the link in my view as follows: It has certain functions which I can access once I have the script in my view. But when running I can see that the fucntions are not called instead i`m getting the error message Object expected at line 104. Why am I having this error and how can I solve it?

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  • Where are the function literals in c++?

    - by academicRobot
    First of all, maybe literals is not the right term for this concept, but its the closest I could think of (not literals in the sense of functions as first class citizens). The idea is that when you make a conventional function call, it compiles to something like this: callq <immediate address> But if you make a function call using a function pointer, it compiles to something like this: mov <memory location>,%rax callq *%rax Which is all well and good. However, what if I'm writing a template library that requires a callback of some sort with a specified argument list and the user of the library is expected to know what function they want to call at compile time? Then I would like to write my template to accept a function literal as a template parameter. So, similar to template <int int_literal> struct my_template {...};` I'd like to write template <func_literal_t func_literal> struct my_template {...}; and have calls to func_literal within my_template compile to callq <immediate address>. Is there a facility in C++ for this, or a work around to achieve the same effect? If not, why not (e.g. some cataclysmic side effects)? How about C++0x or another language? Solutions that are not portable are fine. Solutions that include the use of member function pointers would be ideal. I'm not particularly interested in being told "You are a <socially unacceptable term for a person of low IQ>, just use function pointers/functors." This is a curiosity based question, and it seems that it might be useful in some (albeit limited) applications. It seems like this should be possible since function names are just placeholders for a (relative) memory address, so why not allow more liberal use (e.g. aliasing) of this placeholder. p.s. I use function pointers and functions objects all the the time and they are great. But this post got me thinking about the don't pay for what you don't use principle in relation to function calls, and it seems like forcing the use of function pointers or similar facility when the function is known at compile time is a violation of this principle, though a small one.

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  • 'Locale' configuration and its relationship with Windows API

    - by The Kaykay
    Can the locale configuration of a system OR the keyboard type configuration of that system in anyway affect which API is called at the Kernel level? To be specific, if a program is invoking 'CreateFile()' API then the windows API documentation says that the call gets delegated to either CreateFileA or CreateFileW. If that program is being run on a system present in China with a Chinese Keyboard then which of the two functions will be called?

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  • Nested Execution Flow Control

    - by chris
    I've read tens of answers related to callbacks, promises and other ways to control flow, but I can't still wrap my head around this task, obviously due to my lack of competence. I have a nested problem: In test_1() (and the other functions) I would like to ensure that the rows are added to the table according to the order in which the elements are in the object; I would like to execute either test_2 or test_3 (or both after each other) only after test_1 has finished completely. Actually the right sequence will only be known at runtime (there will be a switch with the possible sequences, like 1,2,3 or 1,3,2 or 1,2,1,3 or 1,3,3,2, etc...) Code: $(function () { // create table tbl = document.createElement('table'); tbl.className = "mainTbl"; $("body").append(tbl); }); function test_1() { $.each(obj, function () { var img = new Image(); img.onload = function () { // add row of data to table var row = tbl.insertRow(-1); var c1 = row.insertCell(0); c1.innerHTML = "loaded"; }; img.onerror = function () { // add row of data to table var row = tbl.insertRow(-1); var c1 = row.insertCell(0); c1.innerHTML = "not loaded"; }; img.src = this.url; }); } function test_2() { $.each(obj, function () { var img = new Image(); img.onload = function () { // add row of data to table var row = tbl.insertRow(-1); var c1 = row.insertCell(0); c1.innerHTML = "loaded"; }; img.onerror = function () { // add row of data to table var row = tbl.insertRow(-1); var c1 = row.insertCell(0); c1.innerHTML = "not loaded"; }; img.src = this.url; }); } function test_3() { $.each(obj, function () { var img = new Image(); img.onload = function () { // add row of data to table var row = tbl.insertRow(-1); var c1 = row.insertCell(0); c1.innerHTML = "loaded"; }; img.onerror = function () { // add row of data to table var row = tbl.insertRow(-1); var c1 = row.insertCell(0); c1.innerHTML = "not loaded"; }; img.src = this.url; }); } I know that calling the functions in sequence doesn't work as they don't wait for each other... I think promises are they way to go but I can't find the right combination and the documentation is way too complex for my skills. What's the best way to structure the code so that it's executed in the right order?

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  • What is the difference between a private and public funtion?

    - by Kyle
    I am a new programmer, and I started in C and am now starting to enjoy JavaScript and a tiny bit of PHP more. Lately I've heard the terms 'private' and 'public' functions a lot. Could anybody give an explanation of the both and how they are of use to a programmer? And I'm probably totally wrong here... but is a (function(){}) in javascript a private function?

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  • Dreamweaver javascript code hints

    - by xdevel2000
    I'd to use DW cs 4 but before to buy I want to test javascript code hints. However that feature doesn't work at all. I have an external .js library and then into an html file I load it but when I type functions or object by name nothing happen. Any idea?

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  • color objects in C or C ++ [closed]

    - by jazz
    Possible Duplicate: Colors in C language i copied a game from a book which name is paratrooper i ask this question again i also provide the code of the objects which i create there i want to change the color of these objects but i didn't understand how to do that so can any one plz help me how to do that.Listen guys they are not the standard functions but i use the graphics library for these functions and i can't find the function in the library file of graphics. i hope u understand know.this code will not run properly so plz tell me something about the function which color it i can't put the image other wize i show u the image it will make alot easieer #include "graphics.h" #include "stdio.h" #include "conio.h" #include "process.h" #include "alloc.h" #include "stdlib.h" #include "math.h" #include "dos.h" main() { int gm=CGAHI, gd=CGA, key=0, area; initgraph(&gd, &gm, "C:\\tc\\bgi"); helidraw(246,50,-1); getch(); return 0; } helidraw ( int x, int y, int d ) { int direction, i, j ; if ( d ) direction = -1 ; else direction = 1 ; i = 3 ; j = 8 ; line ( x - j - 8, y - i - 2, x + j + 8, y - i - 2 ) ; line ( x - j + 5, y - i - 1, x + j - 5, y - i - 1 ) ; line ( x - j, y - i, x + j, y - i ) ; for ( ; i > 0 ; i--, j += 2 ) { putpixel ( x - ( direction * j ), y - i, 1 ) ; line ( x + ( direction * j ), y - i, x + ( direction * ( j - 8 ) ), y - i ) ; } i = 0 ; j -= 2 ; line ( x - ( direction * j ), y - i, x - ( direction * ( j + 17 ) ), y - i ) ; line ( x - ( direction * j ), y - i + 1, x - ( direction * ( j + 7 ) ), y - i + 1 ) ; putpixel ( x - ( direction * ( j + 19 ) ), y - i - 1, 1 ) ; for ( ; i < 3 ; i++, j -= 2 ) { putpixel ( x - j, y + i, 1 ) ; putpixel ( x + j, y + i, 1 ) ; } line ( x - j, y + i, x + j, y + i ) ; putpixel ( x - j + 3, y + i + 1, 1 ) ; putpixel ( x + j - 3, y + i + 1, 1 ) ; line ( x - j - 10, y + i + 2, x + j + 10, y + i + 2 ) ; putpixel ( x + ( direction * ( j + 12 ) ), y + i + 1, 1 ) ; }

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  • Why should GoTos be bad?

    - by lisn
    I'm using gotos and a lot of them. C++, PHP or COBOL - I use them on nearly all occasions where everybody else would use functions or even classes. Yet my code is Clear Maintainable Bug-free Fast So why does everybody I meet tell me about how bad gotos are? Are there any facts that show that they are "bad"?

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  • C++ undefined reference

    - by klaus-johan
    Hi , My problem is the following : I have a class A that inherits from an abstract base class. I override all the virtual functions from the base class, and I have a constructor like this : A::A(B* b) { this->b=b; } In the constructor of class B , I have the following piece of code: A* a=new A(this) However this line of code gives the error : undefined reference to 'A::A(B*)' I have absolutly no idea why could this be happening , so any suggestion would be greatly appreciated !

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