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# FAQ Topic - Why does simple decimal arithmetic give strange results? (2008-06-21)

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### FAQ server

Jun 20, 2008, 7:00:02 PM6/20/08
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FAQ Topic - Why does simple decimal arithmetic give strange
results?
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For example, 5*1.015 does not give exactly 5.075 and 0.06+0.01 does
not give exactly 0.07 in javascript.

Javascript numbers are represented in binary as IEEE-754 (IEC 559)
Doubles, with a resolution of 53 bits, giving an accuracy of
15-16 decimal digits; integers up to about 9e15 are precise, but
few decimal fractions are. Given this, arithmetic is as exact
as possible, but no more. Operations on integers are exact if
the true result and all intermediates are integers within that
range.

In particular, non-integer results should not normally be
compared for equality; and non-integer computed results
commonly need rounding; see 4.6.

http://msdn2.microsoft.com/en-us/library/7wkd9z69.aspx

http://www.merlyn.demon.co.uk/js-misc0.htm#DW4

Otherwise, use Math.round on the results of expressions which
should be of integer value.

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### Dr J R Stockton

Jun 21, 2008, 4:07:04 PM6/21/08
to
In comp.lang.javascript message <485c3675\$0\$90273\$1472...@news.sunsite.
dk>, Fri, 20 Jun 2008 23:00:02, FAQ server <javas...@dotinternet.be>
posted:

> The FAQ workers are a group of volunteers.

That needs to be changed. At present they are effectively an empty set.

--
(c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05.
Web <URL:http://www.merlyn.demon.co.uk/> - w. FAQish topics, links, acronyms
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