sub string_round
{
    my $num = shift;
    my $pre = shift;

    my $dot = index($num, q{.});
    my $_e_ = index($num, q{e});
    if ( $[ <= $_e_ ) {
        my $exp = substr($num, $_e_+1); # Capture exp portion.
        $num = substr($num, 0, $_e_);   # Remove the exp portion.
        if ( $[ > $dot ) {
            $dot = $_e_;  # Has exp, no dot, set it to where the e was
        }
        else {            # Remove the dot
            $num = ( substr($num, 0, $dot) . substr($num, $dot+1) );
        }

        if (0!=$exp && ( -1 == ($exp/abs($exp)))) {  # Negative exponent.

            # Numbers available (from $[ to $dot) 
            #  are within precison, after exponent is applied (exp - $dot)
            if ( (abs($exp)-$dot+$[) <= $pre ) {
                for ( my $cx = 0; $cx < abs($exp); $cx++ )
                {
                    $dot--;
                    if ( $dot < $[ ) {
                        $num = "0$num";
                        $dot++;
                    }
                }
            }
            elsif ( abs($exp) > abs($dot-$pre+$[) ) {
                return 0;
            }
            else {
                for ( my $cx = 0; $cx < (abs($exp)-$dot+$[); $cx++ )
                {
                    $dot--;
                }
            }
            if ( $[ < $dot ) {
                $num = ( substr($num, 0, $[+$dot)
                        . "." . substr($num, $[+$dot ) );
            }
            else {
                $num = "0.$num";
                $dot = $[ + 1;
            }
        }
        else {                                  # Positive exponent.
            my $cx = 0;

            # Dot already removed from number
            # If $cx is less than exponent, walk along the number
            #  (starting from where . was).
            for ( ; $cx < $exp; $cx++ ) {

                # If , somehow, $[ + $dot + $cx
                # ... is beyond the length of the string
                # cath up by adding more zeroes.
                while (( $[ + $dot + $cx ) >= length($num) ) {
                    $num .= "0";
                }
            }

            # Maybe I didn't add any zeroes.
            #  $[ + $dot + $cx is still shorter then length
            #  ... so, the number still has a dot,
            #  and maybe still needs rounding.
            if (( $[ + $dot + $cx ) < (length($num)) ) {
                $dot = ( $dot + $exp );
                $num = ( substr($num, 0, $[+$dot)
                        . "." . substr($num, $[+$dot ) );
            }
            else {

                # Already at end of string, just return the whole number.
                $dot = $[ - 1;
                return $num;
            }
        }
    } # End $_e_  ( exponent has been eliminated )
    if ( $[ <= $dot ) {
        my $aPre = $[ + $dot + $pre;
        if ( length($num) >= $aPre ) {
            my $aCho = $aPre + 1;
            my $cho = substr($num, $aCho, 1);
            $num = substr($num, 0, $aCho); # Cut off num at expected length.
            if ( 5 <= $cho ) {
SREV:           for ( my $cx = $aPre; 0 <= $cx; $cx-- ) {
                    my $noch = substr($num, $cx, 1);
                    if (0==$cx) {
                        if ( q{.} eq $noch) {
                            $num = "1" . $num;
                        }
                        elsif ( q{9} eq $noch) {
                            substr($num, $cx, 1) = "0";
                            $num = "1" . $num;
                        }
                        else {
                            substr($num, $cx, 1) = ($noch + 1);
                        }
                        last SREV;
                    }
                    elsif ( q{.} eq $noch ) {
                        next SREV;
                    }
                    elsif ( 9 != $noch ) {
                        substr($num, $cx, 1) = ($noch + 1);
                        last SREV;
                    }
                    else {
                        substr($num, $cx, 1) = "0";
                    }
                }
            }
        }
    }
    return $num;
}