Perhaps the word you are missing is 'magnitude'.

Try this:

#! perl -slw
use strict;

sub log10{ log( $_[0] ) / log( 10 ) }
sub magnitude{ int log10( $_[0] ) }
sub sign { $_[0] <=> 0 }

my @nums = sort{
    $b <=> $a
} qw[ 1.3e-3 3.7e-5 102 46 1e-4 1e-12 ];

my @byMag;
my $prev = $nums[ 0 ];
for my $i ( 1 .. $#nums ) {
    my $this = $nums[ $i ];
    my $diff = abs( magnitude( $prev ) - magnitude( $this ) );
    --$diff if sign( magnitude( $this ) ) == sign( magnitude( $prev ) 
+);

    push @byMag, $prev;
    push @byMag, ( 0 ) x $diff if $diff > 1;
    $prev = $this;
}
push @byMag, $prev;

print for @byMag;

__END__
C:\test>1054890.pl
102
46
0
0
0
1.3e-3
1e-4
3.7e-5
0
0
0
0
0
0
1e-12
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