how can I speed this up?

[rbi]

Hi,
I have translated a program from FORTRAN to perl.
When I run it as FORTRAN-compiled executable, it is at least 4 times faster than perl, on input files of about 120000 records.
Since I'm a beginner, I'm sure the perl I've written is not very good... In particular, in (1) I prepare a $tmp string through a loop to be printed. the subroutine decode might have problems too... I've replicated the FORTRAN code and there I compute the exponential, but maybe string manipulation can do much better...
Thanks in advance for any corrections/suggestions
Roberto

# here some initialisation or operations on small
# vectors

     ....
            $nvar = 9;
     ....
            foreach $k (1..$nvar) {
                $record = <IN>;
                chomp($record);
                @values = &decode($record,$nt,$val_m);
                foreach $it (1..$nt) {
                  if ($values[$it-1] < 0 and $values[$it-1] != $val_m)
+ {
                     die "error: found negative value.\n";
                  }
                  $field[$it-1][$k-1] = $values[$it-1];
                }
            }
            foreach $it (1..$nt) {
                $tmp  = sprintf "%s", $some_vector[$it-1];
                foreach $k (1..$nvar) {
                   $tmp = $tmp.sprintf " %11.4E", $field[$it-1][$k-1];

  #   (1)  in Fortran this should be a single write intruction with
           FORMAT ('i4.4,4i2.2,9(1x,1pe11.4))')
                }
               $tmp = $tmp."\n";
               print OUT $tmp;
            }

#     (2) this is seems to go the same speed as the one above ...
#
#           foreach $it (1..$nt) {
#               printf OUT "%s", $some_vector[$it-1];
#               foreach $k (1..$nvar) {
#                  printf OUT " %11.4E", $field[$it-1][$k-1];
#               }
#               print OUT "\n";
#           }
               ....


sub decode() {

# this routine should decode the $record where there are a series of
# $nt decimal fractions in the first part of the string 
# (5*$nt characters),and exponents in the last decimal fractions are
# written as 5-digit integers, and must be multiplied by 10.**(-5),
# negative exponents are coded as 2-digit odd numbers, while positive
# exponents are even numbers
# 12345...01... where 01 are characters $nt*5 and $nt*5+1 will give
# 1.234E-01

   my $record = shift();
   my $nt = shift();
   my $val_missing = shift();

   $lmina = 0;
   $lminb = 5 * $nt;
   foreach $it (1..$nt) {
      $ia = substr($record,$lmina,5);
      $ib = substr($record,$lminb,2);
      if ($ia ==  0 and $ib == 99) {
         $values[$it-1] = $val_missing;
      } else {
         $x1 = $ia  * 10.**(-5);
      if (($ib % 2) == 0) {
            $x2 = 10.**($ib/2);
         } else {
            $x2 = 10.**(-($ib+1)/2);
         }
         $values[$it-1] = $x1 * $x2;
      }
      $lmina = $lmina + 5;
      $lminb = $lminb + 2;
   }
   return @values;
}