How to convert bigint to byte array in perl similar as java - arrays

Question

I am trying to replicate some java code in perl.
The operation, I need to perform is to convert Java BigInteger to byte array
Java Code:
public class Main {
public static void main(String[] args) {
BigInteger n = new BigInteger("1677259342285725925376");
System.out.println(Arrays.toString(n.toByteArray()));
}
}
Output: [90, -20, -90, 53, 78, -38, 2, -128, 0]
As, new in perl, tried to search and got help from https://www.perlmonks.org/?node_id=229290
Perl Code:
sub bigint_to_bytearray {
my $bigint = shift;
my #bytes;
while(1) {
my ($q,$r) = $bigint->brsft(8);
push(#bytes,$r+0);
last if $q == 0;
$bigint = Math::BigInt->new($q);
}
return #bytes;
}
$n = new Math::BigInt('1677259342285725925376');
my #array = bigint_to_bytearray($n);
print "\\tOUTPUT ARRAY = ", join ', ', #array, "\n";
I am getting error
Use of uninitialized value $r in addition (+) at path/test.pl line 11.
Use of uninitialized value $r in addition (+) at path/test.pl line 11.
Use of uninitialized value $r in addition (+) at path/test.pl line 11.
Use of uninitialized value $r in addition (+) at path/test.pl line 11.
Use of uninitialized value $r in addition (+) at path/test.pl line 11.
Use of uninitialized value $r in addition (+) at path/test.pl line 11.
Use of uninitialized value $r in addition (+) at path/test.pl line 11.
Use of uninitialized value $r in addition (+) at path/test.pl line 11.

Answer 1

This doesn't support negative numbers.
sub bigint_to_bytearray {
my $bigint = shift;
die "Negative numbers not supported" if $bigint->is_neg;
my #bytes = unpack('c*', $bigint->to_bytes);
unshift #bytes, 0x00 if $bytes[0] < 0; # Add sign bit if necessary.
return #bytes;
}
The above requires a relatively new version of Math::BigInt. The following is less efficient, but it works on far older versions:
sub bigint_to_bytearray {
my $bigint = shift;
die "Negative numbers not supported" if $bigint->is_neg;
my #bytes = unpack('c*', pack('H*', substr($bigint->as_hex, 2)));
unshift #bytes, 0x00 if $bytes[0] < 0; # Add sign bit if necessary.
return #bytes;
}
my #bytes = unpack('c*', $bigint->to_bytes);
can be replaced with
my #bytes =
map { $_ >= 0x80 ? 0x100 - $_ : $_ }
map ord,
split //,
$bigint->to_bytes;
and
my #bytes = unpack('c*', pack('H*', substr($bigint->as_hex, 2)));
can be replaced with
my $hex = substr($bigint->as_hex, 2);
$hex = "0$hex" if length($hex) % 2;
my #bytes =
map { $_ >= 0x80 ? 0x100 - $_ : $_ }
map hex,
$hex =~ /../g;