use Inline C;
use strict;
use warnings;

my $x = "012\xf0ABC\x0f\x00\x01\xff";

print unpack("H*", $x ), "\n";    #  303132f04142430f0001ff

flipbits( $x, length $x );

print unpack("H*", $x ), "\n";    #  cfcecd0fbebdbcf0fffe00

__END__

__C__

void flipbits(char* a, int len ) {

  for ( ; len--  ; ++a ) *a ^= 0xff;

}