16进制数转换成10进制数，通过Math:BigInt模块实现
#!/usr/bin/perl

use warnings;
use strict;
use Math::BigInt;

my %hex_hash = (0=>0, 1=>1, 2=>2, 3=>3, 4=>4, 5=>5, 6=>6,
  7=>7, 8=>8, 9=>9, a=>10, b=>11, c=>12, d=>13, e=>14, f=>15);
    
sub hex_to_dec{
  my $data = shift;
  my $index = shift;
  --$index;
  my $result = Math::BigInt->new(0);
  my $factor = Math::BigInt->new(1);
  while($index >=2 ){
    my $digit = substr($data, $index, 1);
    if ($digit =~/[a-fA-F]/){
      $digit = lc $digit;
      $digit = $hex_hash{$digit};
    }
    my $temp = Math::BigInt->new($digit);
    $temp->bmul($factor);
    $result->badd($temp);
    --$index;
    $factor->bmul(16);
  }
  return $result;
}
print hex_to_dec("0x10", length("0x10")), "\n";
print hex_to_dec("0xfff", length("0xfff")), "\n";