in reply to Optimize bit stream conversion

Use pack to get the bytes from the binary representation:
#!/usr/bin/perl
use warnings;
use strict;

my @bits = (
  1, 0, 0, 0, 0, 0, 1, 0,   # A / 0x41 / 0b01000001
  0, 1, 0, 0, 0, 0, 1, 0,   # B / 0x42 / 0b01000010
  1, 1, 0, 0, 1, 0, 1       # incomplete byte
);

my $string = join q(), @bits;
my $incomplete = @bits % 8 || -@bits;             # The || part handle
+s complete bytes.
print pack "b*", substr $string, 0, -$incomplete;

splice @bits, 0, -$incomplete;                    # Remove the process
+ed part.
print "\n@bits\n";

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Update: handle complete bytes (new secret operator %8||-).
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

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Re^2: Optimize bit stream conversion
by Monk::Thomas (Friar) on Jul 30, 2015 at 12:19 UTC

    Ah! That's nice.

    I condensed it into:

    #!/usr/bin/perl

use strict;
use warnings;

# store 'A' and 'B' as a bitstream
# (bit groups are stored big endian!)
my @bits = (
  1, 0, 0, 0, 0, 0, 1, 0,   # A / 0x41 / 0b01000001
  0, 1, 0, 0, 0, 0, 1, 0,   # B / 0x42 / 0b01000010
  1, 1, 0, 0, 1, 0, 1       # incomplete byte
);

my $data  = pack "b*", join q{}, splice @bits, 0, -(@bits % 8);

printf "data: %s\n", $data;                # AB
printf "bits: %s\n", join ', ', @bits;     # 1, 1, 0, 0, 1, 0, 1

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    Update

    Both variations do not convert properly if there actually isn't an incomplete byte. This version works:

    # variant a) using floor()
use POSIX;
$data = pack 'b*', join q{}, splice @bits, 0, POSIX::floor(@bits / 8) 
+* 8;

# variant b) using int
$data = pack 'b*', join q{}, splice @bits, 0, int(@bits / 8) * 8;

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      I didn't want to confuse you with a terse code. Updated the original node with a correct solution.
      لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ
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