crc32 function for playdate lua. only works on strings.

crc32.lua

local CRC32_LUT = nil

local function crc32_init()
  if not CRC32_LUT then
    CRC32_LUT = table.create(255, 0)
    local rem
    for i = 0, 255 do
      rem = i
      for j = 1, 8 do
        if (rem & 1 == 1) then
          rem = rem >> 1
          rem = rem ~ 0xEDB88320
        else
          rem = rem >> 1
        end
      end
      CRC32_LUT[i] = rem
    end
  end
end

function crc32(str)
  crc32_init()
  local size = #str
  local crc = 0xFFFFFFFF
  local c
  for x = 1, size do
    c = str:byte(x)
    crc = (crc >> 8) ~ CRC32_LUT[(crc & 0xFF) ~ c]
  end
  return crc ~ 0xFFFFFFFF
end