When is 632769996261406250 632769996261406200?

[Mike Ratcliffe]

I realize that numeric accuracy is not perfect in JS but from what I
have read in the FAQ etc. it seems that the number 632769996261406250
should be easily handled by JavaScript.

The following:
alert(632769996261406250)

Displays 632769996261406200 ... does anybody know why?

 

[Richard Cornford]

I realize that numeric accuracy is not perfect in JS but from what I
have read in the FAQ etc. it seems that the number 632769996261406250
should be easily handled by JavaScript.

The following:
alert(632769996261406250)

Displays 632769996261406200 ... does anybody know why?

With IEEE double precision floating point numbers the range of
precisely representable positive integers goes up to 2 to the power of
53 (i.e. 9007199254740992), beyond that some integers must be
represented as approximations, and your number is beyond that.

Richard.

 

[RobG]

I realize that numeric accuracy is not perfect in JS but from what I
have read in the FAQ etc. it seems that the number 632769996261406250
should be easily handled by JavaScript.

The following:
alert(632769996261406250)

Displays 632769996261406200 ... does anybody know why?

Richard gave you the precise answer, a rule of thumb is that integers
longer than 15 digits may be approximated.

 

[Mike Ratcliffe]

Richard gave you the precise answer, a rule of thumb is that integers
longer than 15 digits may be approximated.

Integers longer than 15 digits eh? I learn something new every day.

Thanks guys.

 

[Ry Nohryb]

a rule of thumb is that integers
longer than 15 digits may be approximated.

That's so true that the probability of that "may be" is almost
1...

 

[Dr J R Stockton]

In comp.lang.javascript message <e569280f-ff26-4817-b5b8-c12ecf98107b@q2
2g2000yqm.googlegroups.com>, Wed, 11 Aug 2010 10:59:23, Mike Ratcliffe

I realize that numeric accuracy is not perfect in JS but from what I
have read in the FAQ etc. it seems that the number 632769996261406250
should be easily handled by JavaScript.

The following:
alert(632769996261406250)

Displays 632769996261406200 ... does anybody know why?

Yes. Convert your number to binary, getting
+100011001000000011001111010110000011101011111011011000101010
which is 60 bits long. Disregard trailing zeroes, and you have 59 bits
of resolution; a JavaScript Number, which is an IEEE Double, can hold
only 53 significant bits of resolution.

More about Numbers, etc., via sig below.