base64.lua

-- Base64-encoding
-- Sourced from http://en.wikipedia.org/wiki/Base64
-- BSD licensed

require('math')


local index_table = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'


function to_binary(integer)
    local remaining = tonumber(integer)
    local bin_bits = ''

    for i = 7, 0, -1 do
        local current_power = math.pow(2, i)

        if remaining >= current_power then
            bin_bits = bin_bits .. '1'
            remaining = remaining - current_power
        else
            bin_bits = bin_bits .. '0'
        end
    end

    return bin_bits
end

function from_binary(bin_bits)
    return tonumber(bin_bits, 2)
end


function to_base64(to_encode)
    local bit_pattern = ''
    local encoded = ''
    local trailing = ''

    for i = 1, string.len(to_encode) do
        bit_pattern = bit_pattern .. to_binary(string.byte(string.sub(to_encode, i, i)))
    end

    -- Check the number of bytes. If it's not evenly divisible by three,
    -- zero-pad the ending & append on the correct number of ``=``s.
    if math.mod(string.len(bit_pattern), 3) == 2 then
        trailing = '=='
        bit_pattern = bit_pattern .. '0000000000000000'
    elseif math.mod(string.len(bit_pattern), 3) == 1 then
        trailing = '='
        bit_pattern = bit_pattern .. '00000000'
    end

    for i = 1, string.len(bit_pattern), 6 do
        local byte = string.sub(bit_pattern, i, i+5)
        local offset = tonumber(from_binary(byte))
        encoded = encoded .. string.sub(index_table, offset+1, offset+1)
    end

    return string.sub(encoded, 1, -1 - string.len(trailing)) .. trailing
end


function from_base64(to_decode)
    local bit_pattern = ''
    local decoded = ''

    for i = 1, string.len(to_decode) do
        local char = string.sub(to_decode, i, i)

        if char ~= '=' then
            local offset, _ = string.find(index_table, char)

            if offset == nil then
                error("Invalid character '" .. char .. "' found.")
            end

            bit_pattern = bit_pattern .. string.sub(to_binary(offset-1), 3)
        end
    end

    for i = 1, string.len(bit_pattern), 8 do
        local byte = string.sub(bit_pattern, i, i+7)
        decoded = decoded .. string.char(from_binary(byte))
    end

    return decoded
end

test_base64.lua

require('base64')

print(to_base64('Man')) -- 'TWFu'
print(to_base64('leasure.')) -- 'bGVhc3VyZS4='
print(to_base64('pleasure.')) -- 'cGxlYXN1cmUu'
print(to_base64('easure.')) -- 'ZWFzdXJlLg=='
print(to_base64('sure.')) -- 'c3VyZS4='

print(from_base64('TWFu')) -- 'Man'
print(from_base64('bGVhc3VyZS4=')) -- 'leasure.'
print(from_base64('cGxlYXN1cmUu')) -- 'pleasure.'
print(from_base64('ZWFzdXJlLg==')) -- 'easure.'
print(from_base64('c3VyZS4=')) -- 'sure.'

Done to make myself better for being unable to do much of anything with the DCPU-16 spec Notch released.