Last modified: 2013-11-20 13:47:09 UTC

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Bug 56682 - Avoid floating point errors when manipulating decimal values


Summary:	Avoid floating point errors when manipulating decimal values

Status:	VERIFIED FIXED

Product:	MediaWiki extensions
Classification:	Unclassified
Component:	WikidataRepo (Other open bugs)
Version:	unspecified
Hardware:	All All

Importance:	Unprioritized normal (vote)
Target Milestone:	---
Assigned To:	Wikidata bugs

URL:
Whiteboard:	quantityvalue
Keywords:

Depends on:
Blocks:
	Show dependency tree / graph

Reported:	2013-11-06 19:05 UTC by Daniel Kinzler
Modified:	2013-11-20 13:47 UTC (History)
CC List:	4 users (show)

See Also:
Web browser:	---
Mobile Platform:	---
Assignee Huggle Beta Tester:	---

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Description Daniel Kinzler 2013-11-06 19:05:46 UTC

Floating point errors should be avoided when handling/manipulating QueryValue and DecimalValue objects. One situation where such errors frequently show is when adding an uncertainty margin to a base amount to comput the upper and lower bounds of a quantity.

The errors are introduced because DecimalMath, a class that implements basic arithmetical operation on DecimalValue objects, uses float numbers to perform the calculations.

To avoid this, we could use the bcmath library, if it is installed.

Also, smart rounding rules could be employed to reduce the ill effects of floating point errors.

Comment 1 Daniel Kinzler 2013-11-06 19:07:21 UTC

Example:

           "raw": "3+/-0.01\u00b0",
            "value": {
                "amount": "+3",
                "unit": "\u00b0",
                "upperBound": "+3.0099999999999997868371792719699442386627197265625",
                "lowerBound": "+2.9900000000000002131628207280300557613372802734375"
            },
            "type": "quantity"

Comment 2 Gerrit Notification Bot 2013-11-08 14:11:43 UTC

Change 94355 had a related patch set uploaded by Daniel Kinzler:
(bug 56682) DecimalMath now uses bcmath if available

https://gerrit.wikimedia.org/r/94355

Comment 3 Gerrit Notification Bot 2013-11-08 15:06:39 UTC

Change 94367 had a related patch set uploaded by Daniel Kinzler:
(bug #56682) Use DecimalMath for getUncertaintyMargin

https://gerrit.wikimedia.org/r/94367

Comment 4 Gerrit Notification Bot 2013-11-13 17:44:47 UTC

Change 94355 merged by jenkins-bot:
(bug 56682) DecimalMath now uses bcmath if available

https://gerrit.wikimedia.org/r/94355

Comment 5 Gerrit Notification Bot 2013-11-14 15:04:04 UTC

Change 94367 merged by jenkins-bot:
(bug #56682) Use DecimalMath for getUncertaintyMargin.

https://gerrit.wikimedia.org/r/94367

Comment 6 abraham.taherivand 2013-11-20 13:47:09 UTC

Verified in Wikidata demo time.

Wikimedia Bugzilla is closed!

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