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Bug #15164 can php do a substraction? ;)
Submitted: 2002-01-22 09:17 UTC Modified: 2002-01-22 11:13 UTC
Avg. Score:5.0 ± 0.0
Reproduced:1 of 1 (100.0%)
Same Version:0 (0.0%)
Same OS:0 (0.0%)
From: mik at x dot org dot pl Assigned:
Status: Not a bug Package: Math related
PHP Version: 4.1.1 OS: linux 2.2.19
Private report: No CVE-ID: None
 [2002-01-22 09:17 UTC] mik at x dot org dot pl
my previous bug report was 15162. i wrote about (int) cast there.
another bug may be a reason of that.

i do: (267.57 - 267) * 100 
and i get: 57.999999999999
(i expected 57)
[may be i work too much...]

consider this:

$price = 267.57;
$price_dolars = floor($price);
echo "number of cents is: " . ($price - $price_dolars)*100 . "<BR>";


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 [2002-01-22 10:29 UTC]
floats are not supposed to be exact (per definition). do not use them on currencies. calculate cents ant use (agein) number_format() to display them prooperly. No bug in PHP, bogus.
 [2002-01-22 11:02 UTC] mik at x dot org dot pl
what type should i do for currencies, so?

ok. let's don't call it a bug...
let's call it for example a little magic of floats.

but don't u think u could correct it?
 [2002-01-22 11:13 UTC]
lets call it what it is: an inevitable rounding error
that occurs when converting floating point values from
internal binary to human readable decimal format

use integers and count cents instead of dolars
or use for output
as already suggested

by the way: the result is 56.999999..., not 
57.999999..., so you are off by 0.000.....1
not 0.99999..... which is not so bad after 

 [2002-01-23 04:38 UTC] mik at x dot org dot pl
thanks very much for explaining. i haven't link teory with practice (about floats). probably i realy work too much. :)

let me ask one more question:
if i store prices in postgresql as numeric(10,2), how can i secure handle it in php?
could i do: 
$price_c = (int)($psql_num_price * 100); //?
and how to write it back?
$psql_num_price = $price_c / 100; //?

thanks one more time.
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