use strict;
use warnings;
use Time::HiRes 'time';
use GD;
use File::Copy 'copy';

use constant ORIG => 'potw1949a';

my @list;               # list of filenames w/o extension
for ( 1 .. 8 ) {        # 8 copies
    my $s = ORIG . $_;
    push @list, $s;
    copy ORIG . '.jpg', "$s.jpg" or die;
}

############### GD
my $t = time;
for ( @list ) {
GD::Image-> newFromJpeg( "$_.jpg", 1 )
         -> copyRotateInterpolated( 90, 0 )
         -> _file( "$_+.jpg" );
}
printf "GD, sequential, %.2f s\n", time - $t;

############### FreeImage
$t = time;
parallel( \@list );
printf "FreeImage, parallel, %.2f s\n", time - $t;

unlink glob ORIG . '?.jpg';
unlink glob ORIG . '?+.jpg';

use Inline C => config => ccflagsex => '-fopenmp', 
                          LIBS => '-lgomp -lFreeImage';
use Inline C => <<'END_OF_C';

#include <FreeImage.h>
#include <omp.h>

void parallel(SV *array) {
    int i, nfiles, len;
    char *fname, *tmp;
    char **fnames;
    
    nfiles = av_len((AV *)SvRV(array));
    fnames = malloc((nfiles + 1) * sizeof(char*));
    for (i = 0; i <= nfiles; i++) {
        tmp = SvPV(*av_fetch((AV *)SvRV(array), i, 0), len);
        fname = malloc(len + 1);
        memcpy(fname, tmp, len + 1);
        fnames[i] = fname;
    }
    #pragma omp parallel num_threads (4)
    {
        #pragma omp for
        for (i = 0; i <= nfiles; i++) {
            char *src, *dst;
            asprintf(&src, "%s%s", fnames[i], ".jpg" );
            asprintf(&dst, "%s%s", fnames[i], "+.jpg" );
            FreeImage_JPEGTransform(src, dst, FIJPEG_OP_ROTATE_90, 0);
        }
    }
    for (i = 0; i <= nfiles; i++) free(fnames[i]);
    free(fnames);
}
END_OF_C

__END__

GD, sequential, 7.00 s
FreeImage, parallel, 1.14 s