foo.cc: In function 'bool COWtest()':
foo.cc:91:30: warning: array subscript has type 'char' [-Wchar-subscripts]
  for(int i=0;i<len;i++)L[x[i]]++;
                              ^
foo.cc:92:30: warning: array subscript has type 'char' [-Wchar-subscripts]
  for(int i=0;i<47;i++)M[bl[i]]++;
                              ^

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