How convert BCD format to integer in Lua

Question

I need to write a LUA script that can convert a number from a BCD format to an integer. Let's say my initial byte array looks like this:

local bcdArray = {0x73, 0x31, 0x30, 0x00}

If I understand the BCD format correctly, this array should turn into 31337. I have never worked with this programming language before, please help.

My interpretation of these bytes would be either decimal 73313000 or 00303173. — lhf, Apr 26 '23 at 11:32

score 3 · Accepted Answer · answered Apr 26 '23 at 09:02

Here is one solution, avoiding bit logic to support every Lua version.

local bcdArray = {0x73, 0x31, 0x30, 0x00}

local result = 0
for i, b in ipairs(bcdArray) do
    -- Every b encodes 2 decimals
    local b1 = b % 16 -- thus we split them into lower half
    local b2 = math.floor(b / 16) -- and upper half
    
    -- and add both to the result by setting the digit at position i * 2 - 1 and 2 respectively
    result = result + b1 * 10 ^ (i * 2 - 1) + b2 * 10 ^ (i * 2 - 2)
end

print(result)

Keep the maximum integer size in mind!

How convert BCD format to integer in Lua

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