Still vec can be used... differences are minimal:

update: included jmcnamara's code, which is really fast.

#!/usr/bin/perl
use Benchmark qw(cmpthese);

my $buf = chr(1) x 2e6;

cmpthese(-10,
    {
        unpack => sub { # BrowserUk
            join( chr(0), unpack '(A1)*', $buf ) .chr(0)
        },
        substr => sub { # salva
            $out = chr(0) x (length($buf) * 2);
            substr($out, $_ * 2, 1, substr($buf, $_, 1)) for 0..length
+($buf);
            $out;
        },
        vec    => sub { # shmem
            $out = chr(0) x (length($buf) * 2);
            vec($out,$_<<1,8) = vec($buf,$_,8)
                for 0..length($buf)-1;
            $out;
        },
        vec2   => sub { # jmcnamara
             my $out = pack 'v*', unpack 'C*', $buf;
        },
    }
);
__END__
       s/iter    vec unpack substr   vec2
vec      1.44     --    -1%    -3%   -81%
unpack   1.42     1%     --    -2%   -81%
substr   1.40     3%     2%     --   -80%
vec2    0.275   423%   417%   408%     --

[download]

But your unpack routine doesn't seem to work correctly.

qwurx [shmem] ~> wc -c interleave.pl
715
qwurx [shmem] ~> perl interleave.pl
vec: 1430
#!/usr/bin/perl

#my $buf = chr(1) x 2e6;
my $buf = do { local $/; seek DATA,0,0; <DATA> };

my $c = {
    unpack => sub {
        join( chr(0), unpack '(A1)*', $buf ) .chr(0)
    },
    substr => sub {
        my $out = chr(0) x (length($buf) * 2);
        substr($out, $_ * 2, 1, substr($buf, $_, 1)) for 0..length($bu
+f);
        $out;
    },
    vec    => sub {
        my $out = chr(0) x (length($buf) * 2);
        vec($out,$_<<1,8) = vec($buf,$_,8)
            for 0..length($buf)-1;
        $out;
    },
    vec2   => sub {
        my $out = pack 'v*', unpack 'C*', $buf;
    }
};
for (keys %$c) {
    my $out = $c->{$_}->();
    (my $c = $out) =~ s/\0//g;
    print "$_: ",length($out),$/,$c,$/;
}
__DATA__

vec2: 1430
#!/usr/bin/perl

#my $buf = chr(1) x 2e6;
my $buf = do { local $/; seek DATA,0,0; <DATA> };

my $c = {
    unpack => sub {
        join( chr(0), unpack '(A1)*', $buf ) .chr(0)
    },
    substr => sub {
        my $out = chr(0) x (length($buf) * 2);
        substr($out, $_ * 2, 1, substr($buf, $_, 1)) for 0..length($bu
+f);
        $out;
    },
    vec    => sub {
        my $out = chr(0) x (length($buf) * 2);
        vec($out,$_<<1,8) = vec($buf,$_,8)
            for 0..length($buf)-1;
        $out;
    },
    vec2   => sub {
        my $out = pack 'v*', unpack 'C*', $buf;
    }
};
for (keys %$c) {
    my $out = $c->{$_}->();
    (my $c = $out) =~ s/\0//g;
    print "$_: ",length($out),$/,$c,$/;
}
__DATA__

substr: 1430
#!/usr/bin/perl

#my $buf = chr(1) x 2e6;
my $buf = do { local $/; seek DATA,0,0; <DATA> };

my $c = {
    unpack => sub {
        join( chr(0), unpack '(A1)*', $buf ) .chr(0)
    },
    substr => sub {
        my $out = chr(0) x (length($buf) * 2);
        substr($out, $_ * 2, 1, substr($buf, $_, 1)) for 0..length($bu
+f);
        $out;
    },
    vec    => sub {
        my $out = chr(0) x (length($buf) * 2);
        vec($out,$_<<1,8) = vec($buf,$_,8)
            for 0..length($buf)-1;
        $out;
    },
    vec2   => sub {
        my $out = pack 'v*', unpack 'C*', $buf;
    }
};
for (keys %$c) {
    my $out = $c->{$_}->();
    (my $c = $out) =~ s/\0//g;
    print "$_: ",length($out),$/,$c,$/;
}
__DATA__

unpack: 1193
#!/usr/bin/perl#my$buf=chr(1)x2e6;my$buf=do{local$/;seekDATA,0,0;<DATA
+>};my$c={unpack=>sub{join(chr(0),unpack'(A1)*',$buf).chr(0)},substr=>
+sub{my$out=chr(0)x(length($buf)*2);substr($out,$_*2,1,substr($buf,$_,
+1))for0..length($buf);$out;},vec=>sub{my$out=chr(0)x(length($buf)*2);
+vec($out,$_<<1,8)=vec($buf,$_,8)for0..length($buf)-1;$out;},vec2=>sub
+{my$out=pack'v*',unpack'C*',$buf;}};for(keys%$c){my$out=$c->{$_}->();
+(my$c=$out)=~s/\0//g;print"$_:",length($out),$/,$c,$/;}__DATA__

[download]

update2: added jmcnamara's code to the stuff inside readmore tags

In reply to Re^3: Interleaving bytes in a string quickly by shmem
in thread Interleaving bytes in a string quickly by BrowserUk

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