foo.cc: In function 'int main()':
foo.cc:33:45: warning: iteration 3000007 invokes undefined behavior [-Waggressive-loop-optimizations]
   33 |         pre_sumX[i]=pre_sumX[i-1]+bucket_X[i];
      |                                   ~~~~~~~~~~^
foo.cc:31:19: note: within this loop
   31 |     for(int i=1; i<=MAX_M; ++i)
      |                  ~^~~~~~~

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