bytes_to_short(short_to_bytes($x)) is not equal to $x on all platforms. Use v instead. (Using "L" to convert shorts is silly anyway.)

Furthermore, "short" is a very ambiguous term. It doesn't necessarily mean 16 bits, and it definitely doesn't imply unsigned (as your code expects).

sub uint16_to_bytes {
   my ($int) = @_;
   return unpack('C2', pack('v', $int));
}

sub bytes_to_uint16 {
   my ($lo, $hi) = @_;
   return unpack('v', pack('C2', $lo, $hi));
}

sub int16_to_bytes {
   my ($int) = @_;
   return unpack('C2', pack('v', unpack('S', pack('s', $int))));
}

sub bytes_to_int16 {
   my ($lo, $hi) = @_;
   return unpack('s', pack('S', unpack('v', pack('C2', $lo, $hi))));
}
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