Re^3: converting binary to decimal

[LanX]

It's consecutive doubling and adding from left to right

• the first tr doubles every digit mod 10 1->2, ... 5->0, 6->2,...
• the second tr adds a carry bit for every 5-9 -> 1
• since the next bit is appended, the carry bit is shifted to the left
• the | does a bitwise or which adds the bits ²

for example if $n == "08" and the next bit is "1", you'll get "06" | "11" == "17" and so on.

tybalt loves constructing¹ regex-automatons on strings

¹) cryptic

²) this part is a bit (sic ;) voodoo for me

[harangzsolt33]

Hmm... That's amazing. But i tried to break it down into more easily understandable parts for me, and I think I broke it! Can you please show me why it no longer works? EDIT: I think I know what I did wrong. I accidentally doubled the "|" character. I can't even type. X_X

sub binary2decimal
{
  defined $_[0] or return 0;
  my $B = $_[0];

  $B =~ tr|01||cd;                          # Remove illegal chars
  $B =~ s/^0+//;                            # Remove preceding zeros
  my @BITS = split(//, $B);

  my $n = 0;
  my $copy1;
  my $copy2;
  my $copy3;

  foreach (@BITS)
  {
    $copy1 = $n;
    $copy2 = $n;
    $copy1 =~ tr/1-9/246802468/;
    $copy2 =~ tr/1-9/00001/;
    $n = (0 . $copy1 || $copy2 . $_);   # This should be | not ||
    $n =~ s/^0+(?=.)//;
  }
  return $n;
}

[LanX]

Not my code, and far too tricky to maintain in my opinion.

Relying on the idiosyncracies of | is nothing I recommend.

I even have problems to reproduce my own explanation in the debugger.

The original code works tho when tested. 🤷🏻‍♀️

[LanX]

> I even have problems to reproduce my own explanation in the debugger.

And the reason is that it's supposed to be a "bitstring" not "numeric bit" operation.

see https://perldoc.perl.org/perlop#Bitwise-String-Operators

hence replacing | with |. under use feature "bitwise" will stop doing hard to predict things, even after refactoring this golfing code.

ugh...