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  • Performance Optimization for Matrix Rotation

    - by Summer_More_More_Tea
    Hello everyone: I'm now trapped by a performance optimization lab in the book "Computer System from a Programmer's Perspective" described as following: In a N*N matrix M, where N is multiple of 32, the rotate operation can be represented as: Transpose: interchange elements M(i,j) and M(j,i) Exchange rows: Row i is exchanged with row N-1-i A example for matrix rotation(N is 3 instead of 32 for simplicity): ------- ------- |1|2|3| |3|6|9| ------- ------- |4|5|6| after rotate is |2|5|8| ------- ------- |7|8|9| |1|4|7| ------- ------- A naive implementation is: #define RIDX(i,j,n) ((i)*(n)+(j)) void naive_rotate(int dim, pixel *src, pixel *dst) { int i, j; for (i = 0; i < dim; i++) for (j = 0; j < dim; j++) dst[RIDX(dim-1-j, i, dim)] = src[RIDX(i, j, dim)]; } I come up with an idea by inner-loop-unroll. The result is: Code Version Speed Up original 1x unrolled by 2 1.33x unrolled by 4 1.33x unrolled by 8 1.55x unrolled by 16 1.67x unrolled by 32 1.61x I also get a code snippet from pastebin.com that seems can solve this problem: void rotate(int dim, pixel *src, pixel *dst) { int stride = 32; int count = dim >> 5; src += dim - 1; int a1 = count; do { int a2 = dim; do { int a3 = stride; do { *dst++ = *src; src += dim; } while(--a3); src -= dim * stride + 1; dst += dim - stride; } while(--a2); src += dim * (stride + 1); dst -= dim * dim - stride; } while(--a1); } After carefully read the code, I think main idea of this solution is treat 32 rows as a data zone, and perform the rotating operation respectively. Speed up of this version is 1.85x, overwhelming all the loop-unroll version. Here are the questions: In the inner-loop-unroll version, why does increment slow down if the unrolling factor increase, especially change the unrolling factor from 8 to 16, which does not effect the same when switch from 4 to 8? Does the result have some relationship with depth of the CPU pipeline? If the answer is yes, could the degrade of increment reflect pipeline length? What is the probable reason for the optimization of data-zone version? It seems that there is no too much essential difference from the original naive version. EDIT: My test environment is Intel Centrino Duo processor and the verion of gcc is 4.4 Any advice will be highly appreciated! Kind regards!

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  • how to store "2010-03-26 10:13:04 Etc/GMT" mysql?

    - by kkchaitu
    Hi All, I would like to store "2010-03-26 10:13:04 Etc/GMT" value in column of type datetime. when i try to insert it i got exception SQLException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '10:13:04 Etc/GMT', at line 1 how to insert data time with time zone. Thanks in advance. please help me its urgent.

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  • ROR heroku PostGres issue

    - by oelbrenner
    getting error: ActiveRecord::StatementInvalid (PGError: ERROR: argument of HAVING must be type boolean, not type timestamp without time zone controller code snippet: def inactive @number_days = params[:days].to_i || 90 @clients = Client.find(:all, :include = :appointments, :conditions = ["clients.user_id = ? AND appointments.start_time <= ?", current_user.id, @number_days.days.ago], :group = 'client_id', :having = 'MAX(appointments.start_time)' ) end

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  • How do I add values to semi-complex JSON object?

    - by Nick Verheijen
    I'm fairly new to using JSON objects and I'm kinda stuck. I've got an JSON object that was converted from this array: Array ( [status] => success [id] => 1 [name] => Zone 1 [description] => Awesome zone deze.. [tiles] => Array ( // Column for the tile grid [0] => Array ( // Row for the tile grid [0] => Array ( [tileID] => 1 [rotation] => 0 ) [1] => Array ( [tileID] => 1 [rotation] => 0 ) // Etc.. ) [1] => Array // etc.. etc.. ) ) I use this object to render out an isometric grid for my HTML5 Canvas game. I'm building a map editor and to put more tiles on the map, i'll have to add values to this json object. This is how I would do it in PHP: mapData[column][row] = array( 'tileID' => 1, 'rotation' => 0 ); So my question is, how do I achieve this with a JSON object in javascript? Thanks in advance! Nick Update I've ran into an error: can't convert undefined to object mapDataTiles[mouseY][mouseX] = { tileID: editorSelectedTile, rotation: 0 }; This is the code i use for clicking & then saving the new tile to the JSON object. At first I though that one of my parameters was 'undefined', so i logged those to the console but they came out perfectly.. // If there is already a tile placed on these coordinates if( mapDataTiles[mouseX] && mapDataTiles[mouseX][mouseY] ) { mapDataTiles[mouseX][mouseY]['tileID'] = editorSelectedTile; } // If there is no tile placed on these coordinates else { mapDataTiles[mouseX][mouseY] = { tileID: editorSelectedTile, rotation: 0 }; } My variables have the following values: MouseX: 5 MouseY: 17 tileID: 2 Also weird fact, that for some coordinates it does actually work and save new data to the array. mapDataTiles[mouseY][mouseX] = { tileID: editorSelectedTile, rotation: 0 };

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  • Calculate time from timezones in php

    - by Ramya
    Hai I have the system with employees having different timezones in their profile. I would like to show the date according to their timezones specified. The GMT time zone values are placed in the database. could you guys help me

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  • Get remote PC's date time?

    - by David.Chu.ca
    Is there any class available to get a remote PC's date time in .net? In order to do it, I can use a computer name or time zone. For each case, are there different ways to get the current date time? I am using Visual Studio 2005.

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  • Jquery and Hide a div on a click

    - by hann
    hello, i have a little problem with JQuery. Well, i have a and i want to hide this div when an user click in a zone that is not in the like the "notifications" behavior in facebook. The solution that i found is to use jQuery.live() method but i think there is a better way to do it. Thank you.

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  • Porting Oracle Date Manipulation

    - by Grasper
    I need to port this following from Oracle syntax to Postgresql. Both FLO_END_DT and FLO_START_DATE are of type DATE in Oracle, and TIMESTAMP WITHOUT TIME ZONE in Postgresql: SELECT TRUNC( TO_CHAR(ROUND(( FL.FLO_END_DT- FL.FLO_START_DT)* 24), '9999D99'),2) FROM FLOWS FL I am not familiar enough with Oracle to know what it is trying to accomplish. Any ideas?

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  • Postgresql 9.1: ERROR: type "citext" does not exist

    - by gotuskar
    I am trying to execute following query through PgAdmin utility. CREATE TABLE svcr."EventLogs" ("eventId" BIGINT NOT NULL, "eventTime" TIMESTAMP WITH TIME ZONE NOT NULL, "userid" CITEXT, "realmid" CITEXT NOT NULL, "onUserid" CITEXT, "description" TEXT, CONSTRAINT eventlogs_pkey PRIMARY KEY ("eventId")); And I get following error - ERROR: type "citext" does not exist SQL state: 42704 Character: 120 However, following query runs fine - CREATE TABLE svcr."CategoryMap" ("category" INT NOT NULL, "userData" INT NOT NULL); What is wrong with the first query?

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  • Building drag and drop interface on iphone

    - by John Stewart
    I am trying to build an app which will have a bunch of cards that the user needs to drag and drop them onto specific drop zones. How would one go about detecting this and if the card is not on the drop zone then it should slide back. Any suggestions on how to structure this app?

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  • addition of gmt times in php

    - by hunt
    Hi , i have a time zone in 2010-05-04T05:27:00.000Z format which indicates the GMT time and i want to add GMT 10+ in to it using php. i can do that thing using following code but how would i directly add 2010-05-04T05:27:00.000Z and GMT 10+ so that i can get a valid date and time. $offset=10*60*60; $dateFormat="d-m-Y H:i::m:s"; echo $timeNdate=gmdate($dateFormat, time()+$offset);

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  • Web service for Timezone based on Location

    - by Dipal Patel
    Hi, Is there any web service available that returns the information of Time zone based on the location name entered. I am preparing the application where in user will enter the place, based on the place entered, I need the information of the timezone (preferably current time and date) of that particular location. Kindly help me. Regards, Dipal

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  • Convert GMT time to local time

    - by Dibish
    Am getting a GMT time from my server in this format Fri, 18 Oct 2013 11:38:23 GMT My requirement is to convert this time to local time using Javascript, eg:/ if the user is from India, first i need to take the time zone +5.30 and add that to my servertime and convert the time string to the following format 2013-10-18 16:37:06 I tried with following code but not working var date = new Date('Fri, 18 Oct 2013 11:38:23 GMT'); date.toString(); Please help me to solve this issue, Thanks in advance

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  • How can I change timezone in Wordpress 2.9.2?

    - by newbie
    I have changed timezone from General Settings, but that had no effect, time still shows as default UTC time zone. Then I changed timezone in wp-settings.php with date_default_timezone_set('Europe/Helsinki'); but that din't work either. What could be wrong with my settings and why isn't timezone changing?

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  • Javascript timezone solution needed

    - by user198729
    I have unix timestamps from time zone X which is not known, the current timestamp(now()) in TZ X is known 1275143019, how to approach a javascript function so that it can generate the datetime in the users current TZ in the format 2010-05-29 15:32:35 ?

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  • Different values for Time.now when using activerecord

    - by Josué Lima
    I have this weird situation: When I do on rails console Time.now or Time.zone.now I get the same values (suppose they run at the sime time: 2014-06-05 23:38:06 -0300) But when I use Time.now in a query like: Match.where("datetime = ?", Time.now) it returns the time 3 hours ahead! .to_sql output: SELECT `matches`.* FROM `matches` WHERE (datetime = '2014-06-06 02:38:06') any thoughts on that? Rails 4 Mysql 5.5

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  • What does that +0100 value mean in NSDate?

    - by mystify
    When I look at an NSDate value in the debugger, I get something like this: 1.4.2010 22:01:47 +0100 I don't get it what this +0100 is good for. Sometimes it is +0200. Is that supposed to be the time zone or something like that? What's it exactly? How does it affect the "since reference date" value?

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  • How to get portion of the attribute value using jquery

    - by Rachel
    I have attribute value as: <div id = "zone-3a-2f-2f-2fPortal-2fPages-2fHome-2fZones-2fLeft-2f-7ccomponent-3a-2f-2f-2fSpm-2fComponents-2fPromotion-2f" class = "promotion"> Now I want to get only portion of it, say Promotion and its value 2f, how can I get this using jquery ? Do we have built in function for it ?

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  • Way to get a timezone from a zip code?

    - by Vaccano
    Anyone know of a web service or something out there that I could give a zip code and get a time zone back? Or is that something I just need to write myself? If so, any hints or guides on how to do that? I use visual studio 2008 and C#.

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