Re: Extracting bits out of huge numbers
- From: hofer <blabla@xxxxxxxxxx>
- Date: Thu, 31 Jul 2008 02:36:21 -0700 (PDT)
Hi sisiphus,
I'll look at Math::GMP
In the doc I saw an interesting suggestion, which is to use
Math::BigInt, but let it use the faster libraries of Math::GMP.
This means probably, that I would run faste, but would stay backwards
compatible for the ones not having Math::GMP.
The suggested use statement is:
use Math::BigInt lib => 'GMP';
The function Math::GMP::gmp_tstbit() sounds very appealing to test a
few
bits of a big number.
However if I want to extract for example bits [967:13] , then the
approach to shift to the right and logical and then with a mask might
be
faster.
I have to try.
thanks and bye
H
On Jul 30, 4:12 am, sisyphus <sisyphus...@xxxxxxxxx> wrote:
On Jul 29, 10:28 pm, hofer <bla...@xxxxxxxxxx> wrote:
Hi,
I'd like to work with huge integers (> 64 bit precision)
Thus I can't use ordinary perl integers.
I thought Math::BigInt wouldn't be a too bad choice.
It's easy enough go create BigInts.
my $a = Math::BigInt->new("0x7777666655544443333222211110000");
my $b = Math::BigInt->new("0x1111111111111111111111111111111");
Calculating with them is also fine:
$a->badd($b); # $a = $a + $b
Now I would like to extract certain bits out of this huge number:
Example Bits 16 bis 12 should result in 0b00001 == 0x1 == 1
Bits 17 bis 12 should result in 0b100001 == 0x21 == 33
So far I see two ways of doing this conversion.
However I'm not really appealed by either solution.
Do you know anything faster / better or even another CPAN module?
Math::GMP will allow you to access individual bits. I would expect it
to be siginificantly faster than Math::BigInt, though I haven't done
any benchmarking.
use warnings;
use Math::GMP;
$x = Math::GMP->new('12344' x 7);
# print the 10 least siginificant bits:
print Math::GMP::gmp_tstbit($x, $_) for reverse(0..9);
print "\n";
Cheers,
Rob
.
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