c++ - Overflow issues when implementing math formulas -


i heard that, when computing mean value, start+(end-start)/2 differs (start+end)/2 because latter can cause overflow. not quite understand why second 1 can cause overflow while first 1 not. generic rule implement math formula can avoid overflow.

suppose using computer maximum integer value 10 , want compute average of 5 , 7.

the first method (begin + (end-begin)/2) gives

5 + (7-5)/2 == 5 + 2/2 == 6

the second method (begin + end)/2 gives overflow, since intermediate 12 value on maximum value of 10 accept , "wraps over" else (if using unsigned numbers usual wrap 0 if numbers signed negative number!). 

12/2 => overflow occurs => 2/2 == 1

of course, in real computers integers overflow @ large value 2^32 instead of 10, idea same. unfortunately, there no "general" way rid of overflow know of, , depends on particular algorithm using. , event then, things more complicated. can different behaviour depending on number type using under hood , there other kinds of numerical errors worry in addition on , underflow.


Comments

Post a Comment

Popular posts from this blog

java - Play! framework 2.0: How to display multiple image? -

i need display gallery of photos. here template: @(photos: list[photo]) @title = { <bold>gallery</bold> } @main(title,"photo"){ <ul class="thumbnails"> @for(photo <- photos) { <li class="span3"> <a href="#" class="thumbnail"> <img src="@photo.path" alt=""> </a> </li> } </ul> } and here controller method: public static result getphotos() { return ok(views.html.photo.gallery.render(photo.get())); } and here photo bean : @entity public class photo extends model { @id public long id; @required public string label; public string path; public photo(string path, string label) { this.path = path; this.label = label; } private static finder<long, photo> find = new finder<long, photo>( long.class, photo.class); public static list<phot...
Read more

gmail - Is there any documentation for read-only access to the Google Contacts API? -

i want read-only access user's google contacts. there stackoverflow member wanted this, , received following answer : yes, there is, use https://www.googleapis.com/auth/contacts.readonly scope , "view contacts". this exchange reference read-only access google contacts can find using google. simply using access token obtained attempt read usual google contacts api (i.e. https://www.google.com/m8/feeds ) fails insufficient permissions. similarly, using google contacts api on new target fails 404 errors (for example https://www.googleapis.com/auth/contacts.readonly/default/full ). is there documentation anywhere on how use api, or permissible way access google contacts api full read-write access?
Read more

php - Controller/JToolBar not working in Joomla 2.5 -

relevant code: jtoolbarhelper::custom('savecategories', 'save', '', 'save', false, false); ... <input type="hidden" name="controller" value="easyblogcontroller"> according can dig docs , own previous questions, should call savecategories() function in easyblogcontroller . i've tried setting value easyblog , easyblog.php (file name) current easyblogcontroller (class name). clicking on save button refreshes page. not redirect, echo or var_dump test code put in savecategories() function. var_dump ing jrequest::getvar('controller') , 'task' return correct values. creating controller object , using $controller->execute('task'); works. the values going depend on location of controller trying call, , have couple options here. typically there controller in base folder of component (likely components/com_easyblog) in file called controller.php , class name inside ...
Read more