As I understand it you have:

      | 1-2   4-8
----------------
1-2   |  a     b
4-8   |  c     d
16-32 |  e     f
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...the way to do this is to have a row/col -> values mapping, sort that and loop. Ie.

my $row_map = [{min =>  1, max =>  2},
               {min =>  4, max =>  8},
               {min => 16, max => 32}];
my $row = undef;
for (0..2)
{
  if (($row_map->[$_]->{min} <= $y) &&
      ($row_map->[$_]->{max} >= $y))
  { $row = $_; last }
}
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