CUFP
tachyon
snippet
<div class="Description"><p>I have just completed work on [cpan://Math::Trig::Units] with Math::Trig::Degree, Math::Trig::Radian and Math::Trig::Gradian subclasses. Something that has always anoyed me is how float operations return 0.499999999998 or 5.00000000001 when the actual value is 0.5. The approx sub was written for this module.
<p>Because of the limit on the accuracy of the vaule of Pi that is easily
supported via a float you will get values like dsin(30) = 0.49999999999999945
when using degrees (or gradians). This can be fixed using the approx()
function.
<p>By default the approx sub will modify numbers so if we have a number like
0.499999945 with 6 9s or 0.50000012 with 6 0s the number will be rounded to
0.5. It also works on numbers like 5.250000001. This is useful when using
degrees or gradians. In degrees these functions will return 0.5 as expected
<code>
approx(dsin(30))
approx(dcos(30))
</code>
The approx sub takes a second optional argument that specifies how many
0s or 9s in a row will trigger rounding. The default is 6.
<code>
approx($num, 7); # will return 0.5 for 0.500000001 but 0.50000001 if
# that is passed as it only has 6 zeros.
</code>
<p>Numbers that do not fulfill the requisite criteria are returned unchanged.
For example 0.5000001 will not be rounded to 0.5 as it only has 5 0s.
</div>
<CODE>
sub approx {
my ( $num, $dp ) = @_;
$dp ||= 6;
if ( $num =~ m/\d*\.(\d*?)(9{$dp,})\d*/ ) {
my $exp = 10** (length $1 + length $2);
return int(($num * $exp) +1 )/$exp;
}
elsif ( $num =~ m/\d*\.(\d*?)(0{$dp,})\d*/ ) {
my $exp = 10** (length $1 + length $2);
return int($num * $exp)/$exp;
}
else {
return $num;
}
}
</CODE>