expr with large values

Ofloo · Post by **Ofloo** » Sat Apr 10, 2004 6:10 am

% format %.2f [format %e [expr [format %e 9999999999999] * [format %e 9999999999999]]]
100000000000000004764729344.00

but if i calc it with my calc then its not right why is this ..?

stdragon · Post by **stdragon** » Sat Apr 10, 2004 5:56 pm

An easier way to do it is:

expr 9999999999999.0 * 9999999999999.0
1e+26

You got:
100000000000000004764729344

which is the same thing.

The real value is 99999999999980000000000001. So it's approximately right. Not much of a difference between 0.999999999999 and 1.0.

But anyway, the reason is that computers' builtin floating point logic is not 100% accurate. It can only hold a certain amount of precision. To have 100% accuracy you have to use software methods which are slower.

Ofloo · Post by **Ofloo** » Sun Apr 11, 2004 12:52 pm

lol are u serious ? ???

its to create a long ip out of a ipv6 so one ip is next to an other there isn't that mutch difference either so .. i expect a calculation to be right .. not somewhere close to ...

so ur saying this is normal ? lol this sux.

k is there a way to avoid this then ?

Ofloo · Post by **Ofloo** » Sun Apr 11, 2004 1:47 pm

hmm k i think i might of found a way do you know somehow how i can reformat this ::::: to

0:0:0:0:0:0

or :1:f::6: or 2001::d:::

so i have at least a char between every :

also how do i reformat this fe80::20b:cdff:fea4:6c5f%4

to a normal format

000000:000000:000000:000000:000000:000000

stdragon · Post by **stdragon** » Mon Apr 12, 2004 8:27 am

Dude, please don't do ipv6 calculations in floating point. Use integers. Most computers don't have 128 bit builtin integers, so it's kind of unavoidable to split it up.

Ofloo · Post by **Ofloo** » Mon Apr 12, 2004 11:24 am

dude i was planing on doing that the floating point was just to see how i could resolve a sientific notation to a normal figur .. but that doesn't work so .. i found an other way .. dw but tnx for the tip just have to figur out some way to reformat that funny looking format some of it makes sence some of it doesn't .. ill find out sooner or later i always do