Bitwise Operator implementations in native Lua.

bitwise-operators.lua

-- Bitwise Operator implementations in native Lua.

-- Play around with it here: https://replit.com/@irgendwr/lua-bitwise-operators

-- Lua only has native support for bitwise operators since 5.3+
-- see https://www.lua.org/manual/5.3/manual.html#3.4.2
-- and http://lua-users.org/wiki/BitwiseOperators

--[[

  SHIFTING

  Shifting right is essentially just dividing by 2.
  Shifting left  is essentially just multiplying by 2.

  Note that Lua converts numbers to floats when dividing,
  so you need to apply math.floor() to get an integer.

--]]

--[[

  BIT MASKS

  Reading the rightmost ("first") bit can be done by calculating modulo 2 and comparing against 1.
  Odd numbers have the last bit set, while even numbers do not.

  There is a crazy hack for bitwise OR, XOR, AND: https://stackoverflow.com/a/32389020/4884643
  Unfortunately the function is not very readable.

--]]

-- This is a hack for checking if a certain bit is set.
-- pos starts counting at 0; the rightmost bit is the "first" one at pos=0.
function checkBit(value, pos)
  -- shift right by pos
  while pos > 0 and value ~= 0 do
    value = math.floor(value / 2)
    pos = pos - 1
  end
  -- get rightmost ("first") bit
  return value % 2 == 1
end

-- Test prints

value = 7 -- Binary representation: 0111

print("Bits of the number 7 (binary representation: 0111). See code for details.")
print(checkBit(value, 0)) -- => true (1)
print(checkBit(value, 1)) -- => true (1)
print(checkBit(value, 2)) -- => true (1)
print(checkBit(value, 3)) -- => false (0)

Play around with it here: https://replit.com/@irgendwr/lua-bitwise-operators

Lua only has native support for bitwise operators since 5.3+
see https://www.lua.org/manual/5.3/manual.html#3.4.2
and http://lua-users.org/wiki/BitwiseOperators.

Implementation of bitwise operations in Lua 5.1 for non-negative 32-bit integers: https://stackoverflow.com/a/32389020/4884643 (Unfortunately the function is not very readable)

Bitwise-and implementation in pure Lua 5.1: https://stackoverflow.com/a/32387452/4884643 (this one is very readable)