use strict;
use warnings;

my @nums = ( 1.3e-3, 3.7e-5, 102, 46, 1e-4, 1e-12);

@nums = sort { $b <=> $a } @nums;            # biggest number first

my $exp_max = int log($nums[0]) / log(10);   # first=biggest exponent
my $exp     = $exp_max;                      # start exponent
my @res;

while ( @nums ) {
  push @res, $nums[0] >= 10**$exp ? shift @nums : 0;
  $exp--;
}

printf( "\$res[%2d] = %8g   #1e%d\n", $_, $res[$_], $exp_max-$_) for (0..$#res);