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Apr 24, 2012, 2:05 PM

Post #1 of 8 (3957 views)
BigInteger Can't Post

I have some code in C# and I am trying convert to perl.
The code:

            BigInteger exp = new BigInteger("SOME BIG NUMBER", 10); 
BigInteger n = new BigInteger("OTHER BIG NUMBER", 10);
BigInteger integer3 = new BigInteger(str.Substring(1), 0x24);
byte[] bytes = integer3.modPow(exp, n).getBytes();
ASCIIEncoding encoding = new ASCIIEncoding();
return new string(encoding.GetChars(bytes));

the second argument of constructor in BigInteger class is a base system.
the str is the string , something like:


anyway, the final string that is return is "patyczkowona1".
I tried to do this in perl, with using Math::BigInt;.
I found some functions in net that convert an byte array to BigInt and BigInt to array:

# Calculate the bit-width of cells on this system. 

sub count_bits {
my $i = 0;
my $q = ~0x0; # Set all bits
while ( $q ) { # All shifted out?
$q = $q << 1; # Shift left
$i++; # Accum shifts
return $i; # Return bit-width

my $bits = count_bits; # System bit-width.
my $cells = int( $bits / 8 ); # max bytes in array
my $mask = ~0x0; # Full mask = 0xF*
my $top_bit = ~( $mask >> 1 ); # High mask = 0x80*


# Convert a BigInt to an array.
sub bint_to_array {
my $quo = shift;
my $msk = Math::BigInt->new($mask);
my @cls;
until ( $quo->is_zero() ) {
my $rem = $quo->copy(); # Lest modify ruin.
$rem->band($msk); # REM = LSC
$quo->brsft($bits); # QUO = Cells above
unshift @cls, $rem->bstr(); # Keep remainder
return @cls;

# Convert an array to a BigInt.
sub array_to_bint {
my @cls = @_;
my $out = Math::BigInt->new(0);
my $i = 0;
while ( @_ ) {
my $lsc = Math::BigInt->new( pop @_ ); # LSC
$lsc->blsft($bits * $i); # Shift up
$out->bior($lsc); # OR to LSC
return $out;

First, I am converting my string to ascii table, next, this ascii table to BigInt, then I am using bmodpow() function and convert result to array:

my $string = "f4eoy18ien92q667yex54u6xqyd2u6e2j0kjkvtesj4gcbkij6yq93ms7kx4yzxx0gdmj9vrhk7yns371ormeg5j44jkm727tg3"; 
my @ascii = unpack("C*", $string);
my $x = array_to_bint(@ascii);

my $exp = "1699226779513586444311853417832813053444275415713267420973354241696037822738978485422119265005494628039077923965408489035118957525416966246759228390003017";
my $n = "8496133897567932221559267089164065267221377078566337104866771208480189113695076911576868324903413008512741498700587851315525414979963642608998181269527941";


my @a = bint_to_array ($x);

my $z;
foreach $z (@a)
print "arg: $z\n";

But, the results is not like supposed to be:

arg: 8660100782654598831
arg: 15621194053667428015
arg: 13895005360354588697
arg: 7950417416029500606
arg: 12330079340979623579
arg: 145443755943421736
arg: 8563019593306281932
arg: 2707167814207797994

every number supposed to be a ascii number.
I tried to convert every argument of @ascii to base36 (encode_base36() in Math::Base36), but then when I do "my $x = array_to_bint(@ascii);" then $x return "NaN"

Does anyone have any idea what am I doing wrong?
Thanks in advance


Apr 29, 2012, 10:01 AM

Post #2 of 8 (3905 views)
Re: [januszmk] BigInteger [In reply to] Can't Post

Check this a little with small numbers. See if the answer is correct for you data.


use Math::BigInt;
use Math::Base36 ':all';

my $b36 = 'f4eoy18ien92q667yex54u6xqyd2u6e2j0kjkvtesj4gcbkij6yq93ms7kx4yzxx0gdmj9vrhk7yns371ormeg5j44jkm727tg3';
my $exp = Math::BigInt->new('1699226779513586444311853417832813053444275415713267420973354241696037822738978485422119265005494628039077923965408489035118957525416966246759228390003017');
my $n = Math::BigInt->new('8496133897567932221559267089164065267221377078566337104866771208480189113695076911576868324903413008512741498700587851315525414979963642608998181269527941');

$x = Math::BigInt->new(decode_base36($b36));
print "\nAns: ".$x->bstr()."\n\n";


$ ./  

Ans: 8903715056186744936505705128241



May 1, 2012, 5:37 AM

Post #3 of 8 (3862 views)
Re: [histrung] BigInteger [In reply to] Can't Post

Thanks for the answer.
No, it's not that simple. The result must be a array with ascii numbers.
I see that I will have to rewrite (or try) class from c#


May 1, 2012, 6:03 AM

Post #4 of 8 (3848 views)
Re: [januszmk] BigInteger [In reply to] Can't Post

What do you mean by ASCII? Can't you just split string result and convert to ASCII if needed?

@nums = split(//,$x->bstr());

Is the answer correct?


May 1, 2012, 6:17 AM

Post #5 of 8 (3841 views)
Re: [histrung] BigInteger [In reply to] Can't Post

I can't, from 65 to 90 ascii codes are A-Z, from 97 to 122 are a-z, from 48 to 57 are 0-9, and that is why I need result in array of ascii codes, and when I convert from that array to string, then I have to get a string "patyczkowona1"


May 1, 2012, 6:31 AM

Post #6 of 8 (3834 views)
Re: [januszmk] BigInteger [In reply to] Can't Post

If you want it in base36 just call

$str = encode_base36($x);


May 1, 2012, 12:51 PM

Post #7 of 8 (3786 views)
Re: [histrung] BigInteger [In reply to] Can't Post

Not exactly.
This is the BigInteger class from one of project in c#:
when Biginteger class is "executed" in code that I gave in first post, then this:

public BigInteger(string value, int radix)

constructor is executing.
I thought that there can be a easy way to do this in perl, but I was wrong

(This post was edited by januszmk on May 1, 2012, 12:52 PM)


May 3, 2012, 4:21 PM

Post #8 of 8 (2585 views)
Re: [januszmk] BigInteger [In reply to] Can't Post

Ok, I was wrong, I found some library in c++ which is doing almost the same work like in this class in c# and the result was the same like in script you gave me.
I have one more question, could you look at this class at the funcion public byte[] getBytes(), and tell me, if bstr() in Math::BigInt is giving the same result? If not, any idea how to do this?

(This post was edited by januszmk on May 3, 2012, 4:21 PM)


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