Changing the value of a BigInt?

taintme has asked for the wisdom of the Perl Monks concerning the following question:

I have a script that reads values and does some stats.
I have 2 values that I read that are different BigInts and I do the same operations on each pair.
The problem is I seem to not be able to assign a new value to an existing BigInt and I believe my performance is suffering because of it. I have received many emails offering to sell me pills to enhance performance, but I thought I would ask here first.

#before loop
$cntdiff = new Math::BigInt '0';
$predefbi =  new Math::BigInt '0';
# inside read loop
# for example
$firststr = "ffffccbbaa0";
$laststr = "ffffccbbaa9";

# Make sure it is clear that its hex...
$firststr = "0x".$firststr;
$laststr = "0x".$laststr;

$strtcnt = new Math::BigInt $firststr;
$endcnt = new Math::BigInt $laststr;

$cntdiff = $endcnt - $strtcnt;

# the above works OK but if I try something like

$predefbi = $firststr;

# it doesn't seem to work
[download]

Am I SOL on this?

TIA

Comment on Changing the value of a BigInt? Download Code

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Re: Changing the value of a BigInt? by ysth (Canon) on May 13, 2004 at 03:49 UTC
Leaving Math::BigInt out of it, you can't have a scalar have a value like "0xdeadbeef" and have perl treat it as the number 0xdeadbeef; the "0x" header is noticed by the perl compiler when compiling a constant, and by things like Math::BigInt::new that explicitly do so, but when perl numifies a string variable, it only looks for decimal numbers. So "0xfoo" will only have the "0" part recognized as a number. Is there a reason you can't say `$predefbi = new Math::BigInt $firststr;`?	[reply] [d/l]
Re: Re: Changing the value of a BigInt? by hossman (Prior) on May 13, 2004 at 04:33 UTC
Is there a reason you can't say $predefbi = new Math::BigInt $firststr; ? Or even... `$predefbi = $strtcnt;` [download]	[reply] [d/l]
Re: Changing the value of a BigInt? by bart (Canon) on May 13, 2004 at 10:04 UTC
The standard approach to get a Math::BigInt object with a new value, is to make a new Math::BigInt object. Sorry. Even the result of adding two Math::BigInt objects is a new Math::BigInt. Are you using the default Math::BigInt driver? Because that one is in Pure Perl, Math::BigInt::Calc... Use one of the available XS libraries to speed it up, Math::BigInt::BitVect (requires Bit::Vector), Math::BigInt::Pari, or Math::BigInt::GMP. From what I gather, Math::BigInt::FactCalc would be an option too. No I have no idea on which is the fastest option. If you need precompiled binaries, see which one is available for your platform. For ActivePerl/Win32, I can only find precompiled binaries for Math::Bigint::BitVect, so that looks like the best option there. I also stumled across a PPM distribution for something called Math::BigIntFast, another wrapper around Bit::Vector by Steffen Beyer, who also made the latter, which isn't available through a normal CPAN search, yet it is on CPAN. I don't know what is going on there. See also: Re: Predict Random Numbers	[reply]
Re: Changing the value of a BigInt? by thor (Priest) on May 13, 2004 at 03:46 UTC
When I see "doesn't seem to work", I ask "what is it doing, and how does that differ from your expectations?". Without that having been answered, I see that you're assigning the string "0xffffccbbaa0" to something that was a Math::BigInt object... thor	[reply]
Re: Changing the value of a BigInt? by taintme (Acolyte) on May 13, 2004 at 05:20 UTC
Thanks for the replies so far. The thing I was trying to avoid was doing "new" each time I want to jam a different hex value into $strtcnt and $endcnt. Basically these three vars live the whole time the program is running, so I was hoping to have a way to say: `$strtcnt = next_hex_val;` [download] without doing "new" but maybe new isn't what is causing slowness.	[reply] [d/l]
Re: Re: Changing the value of a BigInt? by ysth (Canon) on May 13, 2004 at 05:46 UTC
Then you want to tie it; something like: `{ package Tie::AutoBigInt; use Tie::Scalar; use base "Tie::StdScalar"; sub STORE { $_[0]->SUPER::STORE(new BigInt $_[1]) } } tie $strtcnt, "Tie::AutoBigInt";` [download]	[reply] [d/l]