share/lua/website/quvi/bit.lua

   1
   2 -- quvi
   3 -- Copyright (C) 2010  Toni Gundogdu <legatvs@gmail.com>
   4 --
   5 -- This file is part of quvi <http://quvi.sourceforge.net/>.
   6 --
   7 -- This library is free software; you can redistribute it and/or
   8 -- modify it under the terms of the GNU Lesser General Public
   9 -- License as published by the Free Software Foundation; either
  10 -- version 2.1 of the License, or (at your option) any later version.
  11 --
  12 -- This library is distributed in the hope that it will be useful,
  13 -- but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15 -- Lesser General Public License for more details.
  16 --
  17 -- You should have received a copy of the GNU Lesser General Public
  18 -- License along with this library; if not, write to the Free Software
  19 -- Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  20 -- 02110-1301  USA
  21 --
  22
  23 local M = {}
  24
  25 function M.bit_or (x, y) -- http://is.gd/iVg4x
  26     local p = 1
  27     while p < x do p = p + p end
  28     while p < y do p = p + p end
  29     local z = 0
  30     repeat
  31         if p <= x or p <= y then
  32             z = z + p
  33             if p <= x then x = x - p end
  34             if p <= y then y = y - p end
  35         end
  36         p = p * 0.5
  37     until p < 1
  38     return z
  39 end
  40
  41 -- 1-based indexing
  42 function M.bit (p) return 2 ^ (p - 1) end
  43
  44 -- e.g. "if has_bit (foo, bit (n)) then ..."
  45 function M.has_bit(x, p) return x % (p + p) >= p end
  46
  47 return M
  48
  49 -- vim: set ts=4 sw=4 tw=72 expandtab: