share/common/quvi/bit.lua

   1 -- libquvi-scripts
   2 -- Copyright (C) 2010  Toni Gundogdu <legatvs@gmail.com>
   3 --
   4 -- This file is part of libquvi-scripts <http://quvi.sourceforge.net/>.
   5 --
   6 -- This program is free software: you can redistribute it and/or
   7 -- modify it under the terms of the GNU Affero General Public
   8 -- License as published by the Free Software Foundation, either
   9 -- version 3 of the License, or (at your option) any later version.
  10 --
  11 -- This program is distributed in the hope that it will be useful,
  12 -- but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 -- GNU Affero General Public License for more details.
  15 --
  16 -- You should have received a copy of the GNU Affero General
  17 -- Public License along with this program.  If not, see
  18 -- <http://www.gnu.org/licenses/>.
  19 --
  20
  21 local M = {}
  22
  23 function M.bit_or(x, y) -- http://is.gd/iVg4x
  24   local p = 1
  25   while p < x do p = p + p end
  26   while p < y do p = p + p end
  27   local z = 0
  28   repeat
  29     if p <= x or p <= y then
  30       z = z + p
  31       if p <= x then x = x - p end
  32       if p <= y then y = y - p end
  33     end
  34     p = p * 0.5
  35   until p < 1
  36   return z
  37 end
  38
  39 -- 1-based indexing
  40 function M.bit(p) return 2 ^ (p - 1) end
  41
  42 -- e.g. "if has_bit (foo, bit (n)) then ..."
  43 function M.has_bit(x, p) return x % (p + p) >= p end
  44
  45 return M
  46
  47 -- vim: set ts=2 sw=2 tw=72 expandtab: