fixed rowptr integer width

Author: Sinacam

python/liblinear/liblinear.py

@@ -149,7 +149,9 @@ def csr_to_problem_nojit(l, x_val, x_ind, x_rowptr, prob_val, prob_ind, prob_row
 def csr_to_problem(x, prob):
     # Extra space for termination node and (possibly) bias term
     x_space = prob.x_space = np.empty((x.nnz+x.shape[0]*2), dtype=feature_node)
-    prob.rowptr = x.indptr.copy()
+    # rowptr has to be a 64bit integer because it will later be used for pointer arithmetic,
+    # which overflows when the added pointer points to an address that is numerically high.
+    prob.rowptr = x.indptr.astype(np.int64, copy=True)
     prob.rowptr[1:] += 2*np.arange(1,x.shape[0]+1)
     prob_ind = x_space["index"]
     prob_val = x_space["value"]