use strict;
use warnings;

use Inline C => Config =>
 BUILD_NOISY => 1,
 USING => 'ParseRegExp',
 ;

use Inline C => <<'EOC';

double do_nothing(double x[], int sizeOfX) {
  int index;
  for(index=0; index<sizeOfX; index++)  x[index] = 1;
  return x[0];
}

void do_nothing_c(SV * sv) {
 STRLEN len;
 char * pv;

 pv = SvPV_force(sv, len); /* SvPV() also seems ok */

 do_nothing((double *)pv, len / sizeof(double));

}

EOC

my @in = (2.3, 3.4, 4.5, 5.6, 6.7);
my @ret = do_nothing(@in);
print "@in\n@ret\n";


sub do_nothing {
  my $doubles = pack 'd*', @_;
  do_nothing_c($doubles);
  return unpack 'd*', $doubles;
}

__END__

Outputs:
2.3 3.4 4.5 5.6 6.7
1 1 1 1 1

##</code><code>##

void do_nothing(double x[], int sizeOfX) {
  int index;
  for(index=0; index<sizeOfX; index++)  x[index] = 1;
}