>
>Hello php-windows,
>
>for example..
>look at this simple script..
>====================================
><?
> $old=10003.28;
> $new=$old-10000;
> echo $new;
>
>?>
>====================================
>it returns
>3.2800000000007
>it must return
>3.28
>does anyone know what is problem..
>i know that number_format function can ne used here...
>but i want to know that is it bug in php
Computers uses discrete numbers so there are not able to
represent an real numbers properly, because of the hardware
architecture. Therefor computers need to use a fractal
representation for real number. This line is not smooth,
but cut with regions of irregularities considering the
discrete steps between the numbers.
It does not like
1.00001
1.00002
1.00003
1.00004
1.00005
1.00006
1.00007
1.00008
1.00009
1.00010
But more like
1.00001
1.00002
1.00003
1.000035
1.00004
1.00005
1.00006
1.00007
1.00008
1.000095
1.00010
If you imagine the last digit, and plot this,
you will mostly have a smooth straight line, but some times
small hills. Or rather small region with a little bit
higher granularity and other with less granularity.
So when the granularity get smaller and smaller you will
start to experience jumps between the "real" numbers. This
will not happen all the time, but often enough to be notable.
These "bugs" might be the cause of rounding errors while
big transaction is done. But there is techniques to work
around it.
Anyhow, one can esily test this to convinve you self about
where the critical regions appears with a program simlar
to the one below:
void main (void)
{
float i = 1;
while (i > 0.999) {
i -= 0.0000005;
cout << i << endl;
}
}
When the program runs it look fine in the begining.
1
0.999999
0.999999
0.999998
0.999998
0.999997
0.999997
0.999996
0.999996
0.999995
0.999995
0.999994
0.999994
0.999993
0.999993
0.999992
0.999992
0.999991
0.999991
0.999990 <-
0.999990 <-
0.999990 <-
0.999989
0.999989
But check out what happens above here.
0.999988
0.999988
0.999987
0.999987
0.999986
0.999986
0.999985
0.999985
0.999984
0.999984
0.999983
0.999983
0.999982
0.999982
0.999981
0.999981
0.999980
0.999980
Then it looks nice again... But future down we find:
0.999054
0.999054
0.999053 <-
0.999053 <-
0.999053 <-
0.999052
0.999052
And a little bit futher down:
0.999044
0.999044
0.999043 <-
0.999043 <-
0.999043 <-
0.999042
0.999042
And then a bit normal again until:
0.999033
0.999033
0.999032 <-
0.999032 <-
0.999032 <-
0.999031
0.999031
And elsewhere:
0.999280
0.999280
0.999279 <-
0.999279 <-
0.999279 <-
0.999278
0.999278
And just before we quits execution we
still find anomalies:
0.999075
0.999075
0.999074 <-
0.999074 <-
0.999074 <-
0.999073
0.999073
...
0.999023
0.999023
0.999022 <-
0.999022 <-
0.999022 <-
0.999021
0.999021
...
0.999003
0.999003
0.999002 <-
0.999002 <-
0.999002 <-
0.999001
0.999001
0.999000
0.999000
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