#!perl
use warnings;
use strict;

# the following subroutines couns the number of bits in an 8-bit integer

sub sadd8_a { # my first solution -- without looking closely to your code
        my($x) = @_;
        my $n = 0;
        for (my $k = 1; $k < 0x100; $k <<= 1) {
                0 != ($x & $k) and $n++;
        }
        $n;
}

sub sadd8_b { # one of your solutions, modified a bit

  my ( $iDays ) = @_;

  my $iRes = 0;
  for ( 1, 2, 4, 8, 16, 32, 64, 128 ){
    if ( $iDays & $_ ){
      $iRes++;
    }
  }

  return $iRes;
}

sub sadd8_c {
        my($x) = @_;
        $x = ($x & 0b01010101) + ($x >> 1 & 0b01010101);
        $x = ($x & 0b00110011) + ($x >> 2 & 0b00110011);
        ($x & 0b00001111) + ($x >> 4);
}

# let's print an example
for my $n (0 .. 31) {
        print sadd8_a($n), " ";
}
print "\n";

# test
for my $n (0 .. 255) {
        my $a = sadd8_a($n);
        my $b = sadd8_b($n);
        my $c = sadd8_c($n);
        $a == $b && $b == $c or
                die "wrong results: $n $a $b $c";
}

__END__