Re: Bitwise XOR in Lua?

[Roberto Ierusalimschy <roberto@...>]

Follows a poor man's bitlib, for Lua 4.0. It is not close to the real
bitlib, but it is simple and "pure" Lua.

-- Roberto


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local tab = {  -- tab[i][j] = xor(i-1, j-1)
  {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, },
  {1, 0, 3, 2, 5, 4, 7, 6, 9, 8, 11, 10, 13, 12, 15, 14, },
  {2, 3, 0, 1, 6, 7, 4, 5, 10, 11, 8, 9, 14, 15, 12, 13, },
  {3, 2, 1, 0, 7, 6, 5, 4, 11, 10, 9, 8, 15, 14, 13, 12, },
  {4, 5, 6, 7, 0, 1, 2, 3, 12, 13, 14, 15, 8, 9, 10, 11, },
  {5, 4, 7, 6, 1, 0, 3, 2, 13, 12, 15, 14, 9, 8, 11, 10, },
  {6, 7, 4, 5, 2, 3, 0, 1, 14, 15, 12, 13, 10, 11, 8, 9, },
  {7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8, },
  {8, 9, 10, 11, 12, 13, 14, 15, 0, 1, 2, 3, 4, 5, 6, 7, },
  {9, 8, 11, 10, 13, 12, 15, 14, 1, 0, 3, 2, 5, 4, 7, 6, },
  {10, 11, 8, 9, 14, 15, 12, 13, 2, 3, 0, 1, 6, 7, 4, 5, },
  {11, 10, 9, 8, 15, 14, 13, 12, 3, 2, 1, 0, 7, 6, 5, 4, },
  {12, 13, 14, 15, 8, 9, 10, 11, 4, 5, 6, 7, 0, 1, 2, 3, },
  {13, 12, 15, 14, 9, 8, 11, 10, 5, 4, 7, 6, 1, 0, 3, 2, },
  {14, 15, 12, 13, 10, 11, 8, 9, 6, 7, 4, 5, 2, 3, 0, 1, },
  {15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, },
}


function bxor (a,b)
  local res, c = 0, 1
  while a > 0 and b > 0 do
    local a2, b2 = %mod(a, 16), %mod(b, 16)
    res = res + %tab[a2+1][b2+1]*c
    a = (a-a2)/16
    b = (b-b2)/16
    c = c*16
  end
  res = res + a*c + b*c
  return res
end


local ff = 2^32 - 1
function bnot (a) return %ff - a end

function band (a,b) return ((a+b) - bxor(a,b))/2 end

function bor (a,b) return %ff - band(%ff - a, %ff - b) end