in reply to Binary string to base64

I'm in over my head here, but here is a way to get the compression down to 5 characters. 
#results
0000000100100011010001010110011110001001101010111100110111101111  ->  
+  iL1@;

[download]
This almost works. I can only get the last half of the bin string back, but maybe the gurus can see the packing error. Maybe needs 64 bit numbers or Math::BigINT? 
#!/usr/bin/perl
use strict;
use Math::Base85;


my $str = "00000001001000110100010101100111100010011010101111001101111
+01111";

#binary to decimal conversion 
my $num =  unpack("N", pack("B32", substr("0" x 32 . $str, -32)));
print "$num\n";

my $m = Math::Base85::to_base85($num);
print "$str  ->\t$m\n";

#decode it ############################################## 

my $q = Math::Base85::from_base85($m);
print "back to decimal ->\t$q\n";

#I'm losing a 32 bit chunk here 
my $str1 = unpack("B32", pack("N", $q));

print "back to bin ->\n", $str1,"\n";

[download]
I'm not really a human, but I play one on earth. flash japh

Replies are listed 'Best First'.
Re^2: Binary string to base64
by albert (Monk) on Jun 16, 2006 at 18:28 UTC
    Thanks for the suggestion:

    Working within Math::BigInt, it is easy to make the integer by prepending the string with '0b'. Then, between Math::Base85 and Math::BigInt, it is easy to go back and forth, though one needs to prepend '0's after the decoding to get back to the original length. 

    use Math::Base85 qw(from_base85 to_base85);

$str = '0b000000010010001101000101011001111000100110101011110011011110
+1111';

$bint = Math::BigInt->new($str);
$b85str = to_base85($bint);
$bint2 = from_base85($b85str);
print $bint2->as_bin();

    [download]
    This does exactly what I want now. And I get slightly more efficiency than with base64.

    -albert

[reply]
[d/l]
      Hi, I was working on the same thing, but I added a '0b1' so that the leading zeroes in the binary wouldn't get truncated. It condenses it down to 10 characters. Here's my attempt: 
      #!/usr/bin/perl
use Math::BigInt;
use Math::Base85;

my $str = '00000001001000110100010101100111100010011010101111001101111
+01111';
print "$str\n";

#prepend a 0b1 to signal binary and contain leading zeroes  
my $str_p = '0b1'.$str;
print "$str_p\n\n";

my $bignum = Math::BigInt->new($str_p);

my $hex =  $bignum->as_hex();
print "hex $hex\n\n";

my $hex85 = Math::Base85::to_base85($hex);
print "hex85-> $hex85\n\n";

my $hex_back = Math::Base85::from_base85($hex85);
print "hex_back-> $hex_back\n";

my $bignum1 = Math::BigInt->new($hex_back);

my $b_back = $bignum1->as_bin();

#strip off the '0b1'
$b_back = substr($b_back, 3);
print "out-> $b_back\n";
print "in -> $str\n";

      [download]
      I'm not really a human, but I play one on earth. flash japh
[reply]
[d/l]

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