bit array implemented in Lua

bit_array.lua

local M = {}

local BITS_PER_BYTE = 8
local BYTES_PER_INT = string.packsize('j')
local BITS_PER_INT = BITS_PER_BYTE * BYTES_PER_INT

function M.get_bit(h, i)
    local index = i // BITS_PER_INT
    local v = h[index]
    if not v then
        return false
    end

    local mask = 1 << (i % BITS_PER_INT)
    return v & mask ~= 0
end

function M.set_bit(h, i, b)
    local index = i // BITS_PER_INT
    local mask = 1 << (i % BITS_PER_INT)
    local v = h[index]
    if not v then
        if b then
            h[index] = mask
        end
        return
    end

    if b then
        v = v | mask
    else
        v = v & ~mask
    end
    h[index] = v ~= 0 and v or nil
end

return M