"Bitwise AND" in Lua

Question

I'm trying to translate a code from C to Lua and I'm facing a problem. How can I translate a Bitwise AND in Lua? The source C code contains:

if ((command&0x80)==0)
   ...

How can this be done in Lua?

I am using Lua 5.1.4-8

Solution 1

Here is a basic, isolated bitwise-and implementation in pure Lua 5.1:

function bitand(a, b)
    local result = 0
    local bitval = 1
    while a > 0 and b > 0 do
      if a % 2 == 1 and b % 2 == 1 then -- test the rightmost bits
          result = result + bitval      -- set the current bit
      end
      bitval = bitval * 2 -- shift left
      a = math.floor(a/2) -- shift right
      b = math.floor(b/2)
    end
    return result
end

usage:

print(bitand(tonumber("1101", 2), tonumber("1001", 2))) -- prints 9 (1001)

Solution 2

Implementation of bitwise operations in Lua 5.1 for non-negative 32-bit integers

OR, XOR, AND = 1, 3, 4

function bitoper(a, b, oper)
   local r, m, s = 0, 2^31
   repeat
      s,a,b = a+b+m, a%m, b%m
      r,m = r + m*oper%(s-a-b), m/2
   until m < 1
   return r
end

print(bitoper(6,3,OR))   --> 7
print(bitoper(6,3,XOR))  --> 5
print(bitoper(6,3,AND))  --> 2