Decrypting Lua Files from game

I’m truing to decrypt LUA scrpits from cocos2dx game (for wiki).

Links to files of game:
libhellolua.so (cocos2dx external library)
example encrypted LUA-scripts (*.abc files)

I was reading a library in IDA Pro.
This library don’t have mention “xxtea”.

And i found function getEncyptedFileData:
pastebin getEncyptedFileData

This function is not in the original source code of Cocos2d-x.
I think this function is related to decryption (since this function is called nearby with the variable “*.abc”).
I can not understand the some lines in this function:

1: I think that this function CCFileUtils:getFileData.

v5 = (_BYTE *)(*(int (__fastcall **)(cocos2d::CCFileUtils *, const char *, const char *, unsigned int *))(*(_DWORD *)this + 16))(this, a2, "rb", &v26);

2: This loop not readeable. The result of the first line is used in this loop.

do
  {
    v6[(signed int)v17 * (signed __int64)v11 % (unsigned __int64)v14] = *(_BYTE *)(v13 + v16) ^ v15[v17];
    ++v17;
    v16 = (v16 + 1) % v10;
  }
  while ( v17 < v14 );

3: function getEncyptedFileData return result of this line:

v19 = (*(int (__cdecl **)(cocos2d::CCFileUtils *, _BYTE *))(*(_DWORD *)v21 + 24))(v21, v6);

  v5 = (_BYTE *)(*(int (__fastcall **)(cocos2d::CCFileUtils *, const char *, const char *, unsigned int *))(*(_DWORD *)this + 16))(
                  this,
                  a2,
                  "rb",
                  &v26);