> -----Original Message----- > From: Satyam [mailto:Satyam@xxxxxxxxxxxxx] > Sent: Tuesday, March 28, 2006 17:23 > To: enugroho@xxxxxxxxxxxxxxx; Jay Blanchard > Cc: Jeff; php-general@xxxxxxxxxxxxx > Subject: Re: Strange math results > > > Indeed, when doing floating point math, you cannot check the > values for > equality, they will rarely be, you have to check whether the > difference in > between them is less than the error you are willing to > accept. Floating > point numbers are usually an approximation to the actual value and > intermediate operations might pile up errors in each approximation in > different ways. > > As an example, > > $third = 1/3; > > $third will contain 0.33333 up to a certain number of digits, > but it won't > last forever, as it should, theoretically. > > Now, > > $third * 3 == 1 > > will be false, but: > > define('MAXERR',0.0000001); > abs($third * 3 - 1) < MAXERR > > will be true. > > MAXERR is the error you are willing to accept in your > calculations, for > example, if you are using cents, give it a couple of extra > positions so that > roundings don't creep up to significant cents, that is, use > MAXERR = 0.0001 > or thereabouts. > > Satyam > That explains it. Thanks! Jeff -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
