bcpowmod
bc* functions can only generate results of length 18 , is it just on my server (Linux 2.6.18-8.el5 #1 SMP Thu Mar 15 19:57:35 EDT 2007 i686 i686 i386 GNU/Linux) or on everyone's server?
bcscale
(PHP 4, PHP 5)
bcscale — Set default scale parameter for all bc math functions
说明
bool bcscale
( int $scale
)
Sets the default scale parameter for all subsequent bc math functions that do not explicitly specify a scale parameter.
参数
- scale
-
The scale factor.
返回值
如果成功则返回 TRUE，失败则返回 FALSE。
范例
Example#1 bcscale() example
<?php
// default scale : 3
bcscale(3);
echo bcdiv('105', '6.55957'); // 16.007
// this is the same without bcscale()
echo bcdiv('105', '6.55957', 3); // 16.007
?>
add a note
User Contributed Notesbcscale
tangfulin at 126 dot com
05-Jan-2008 07:49
05-Jan-2008 07:49
mwgamera at gmail dot com
06-Dec-2007 10:45
06-Dec-2007 10:45
These functions DO NOT round off your values. No arbitrary precision libraries do it this way. It stops calculating after reaching scale of decimal places, which mean that your value is cut off after scale number of digits, not rounded. To do the rounding use something like this:
<?php
function bcround($number, $scale=0) {
$fix = "5";
for ($i=0;$i<$scale;$i++) $fix="0$fix";
$number = bcadd($number, "0.$fix", $scale+1);
return bcdiv($number, "1.0", $scale);
}
?>
invincible at limitedintelligence dot com
08-Feb-2006 07:50
08-Feb-2006 07:50
If you don't set the default scale, be careful when you're chaining together several BC math functions - since by default, these functions will round off your values, losing accuracy very quickly:
<?php
$a = 1.234
$b = 2.345
$c = 7.890
$ab = bcmul($a,$b); // 2
$abc = bcmul($ab,$c);
echo $abc; // 15
?>
... compare with the answer you get when you use more decimal places:
<?php
$a = 1.234
$b = 2.345
$c = 7.890
bcscale(15);
$ab = bcmul($a,$b); // 2.893730
$abc = bcmul($ab,$c);
echo $abc; // 22.83152970
?>