binary shifts in p::rd exe block

[h. w. neff]

hi.
in an attempt to shift & merge returned results, i find i
   cannot use '>>' or '<<' in a p::rd executable block; i
   must instead divide and multiply, respectively.
e.g. in this code, 'goodrule' works, 'badrule' does not: 

  sub_rule :   /[0-7]/
  goodrule : /reg1/i '=' sub_rule ',' /reg2/i '=' sub_rule ';'
     {
        $main::machineword = $item[3] * 8 | $item[7];
        1
     }
  badrule : /reg1/i '=' sub_rule ',' /reg2/i '=' sub_rule ';'
     {
        $main::machineword = $item[3] << 3 | $item[7];
        1
     }

by 'not working' i mean i get undefined sub-rules and
   such as if i was getting file/stream type redirection
   instead of the shifts i want.
as a result, i've ended up with exe blocks that look like:

   {
      $main::Instruction_upper = 0x440000
                               | ($item[1] / 2048)
                               | $item[4]
                               | ($item[8] / 512)
                               | ($item[10] * 16)
                               | (($item[26] & 0x000010) / 16)
                               | ($item[32] / 2)
                              ;
      $main::Instruction_lower = 0x000000
                               | ($item[14] * 2)
                               | ($item[16] / 2048)
                               | ($item[20] * 16)
                               | ($item[22] / 128)
                               | (($item[26] & 0x00000C) * 1048576)
                               | (($item[28] & 0xC00000) / 16384)
                               | (($item[28] & 0x000003) * 1024)
                               | (($item[34] & 0xC00000) / 1024)
                               | (($item[34] & 0x000003) * 16384)
                              ;
     1
   }

it does what's desired, but from a maintenance point of view
   it is just not clear, without doing some math, what the
   various shifts are.
not to mention the increased chances of a typo in these magic
   numbers!

any ideas about where i've gone wrong in trying to use the
   bit shifts?
or is this a bug in p::rd ?
thanks.
hwn