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);

 

##</code><code>##

$res[ 0] =      102   #1e2
$res[ 1] =       46   #1e1
$res[ 2] =        0   #1e0
$res[ 3] =        0   #1e-1
$res[ 4] =        0   #1e-2
$res[ 5] =   0.0013   #1e-3
$res[ 6] =   0.0001   #1e-4
$res[ 7] =  3.7e-05   #1e-5
$res[ 8] =        0   #1e-6
$res[ 9] =        0   #1e-7
$res[10] =        0   #1e-8
$res[11] =        0   #1e-9
$res[12] =        0   #1e-10
$res[13] =        0   #1e-11
$res[14] =    1e-12   #1e-12