FAQ Topic - Why does simple decimal arithmetic give strange results? (2009-10-07)

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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.

ECMAScript 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 just over ` 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

http://jibbering.com/faq/#formatNumber

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.


The complete comp.lang.javascript FAQ is at
http://jibbering.com/faq/

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