add crc32 function

res/scripts/stdmin.lua

@@ -26,6 +26,38 @@ function __vc_Canvas_set_data(self, data)
     self:_set_data(tostring(_ffi.cast("uintptr_t", canvas_ffi_buffer)))
 end
 
+_ffi.cdef([[
+    unsigned long crc32(unsigned long crc, const char *buf, unsigned len);
+]])
+
+local zlib
+if _ffi.os == "Windows" then
+    zlib = _ffi.load("zlib1")
+elseif _ffi.os == "OSX" then
+    zlib = _ffi.load("z")
+elseif _ffi.os == "Linux" then
+    zlib = _ffi.load("libz.so.1")
+else
+    error("platform does not support zlib " .. _ffi.os)
+end
+
+function crc32(bytes, chksum)
+    local chksum = chksum or 0
+
+    local length = #bytes
+    if type(bytes) == "string" then
+        return zlib.crc32(chksum, bytes, length)
+    elseif type(bytes) == "table" then
+        local buffer = _ffi.new(
+            string.format("char[%s]", length)
+        )
+        for i=1, length do
+            buffer[i - 1] = bytes[i]
+        end
+        return zlib.crc32(chksum, buffer, length)
+    end
+end
+
 -- Check if given table is an array
 function is_array(x)
     if #x > 0 then