/* Returns 1 if the arrays have overlapping data, 0 otherwise */
NPY_NO_EXPORT int
arrays_overlap(PyArrayObject *arr1, PyArrayObject *arr2)
{
npy_uintp start1 = 0, start2 = 0, end1 = 0, end2 = 0;
get_array_memory_extents(arr1, &start1, &end1);
get_array_memory_extents(arr2, &start2, &end2);
return (start1 < end2) && (start2 < end1);
}
/**
* Determine whether two arrays share some memory.
*
* Returns: 0 (no shared memory), 1 (shared memory), or < 0 (failed to solve).
*
* Note that failures to solve can occur due to integer overflows, or effort
* required solving the problem exceeding max_work. The general problem is
* NP-hard and worst case runtime is exponential in the number of dimensions.
* max_work controls the amount of work done, either exact (max_work == -1), only
* a simple memory extent check (max_work == 0), or set an upper bound
* max_work > 0 for the number of solution candidates considered.
*/
NPY_VISIBILITY_HIDDEN mem_overlap_t
solve_may_share_memory(PyArrayObject *a, PyArrayObject *b,
Py_ssize_t max_work)
{
npy_int64 rhs;
diophantine_term_t terms[2*NPY_MAXDIMS+2];
npy_uintp start1 = 0, start2 = 0, end1 = 0, end2 = 0, size1 = 0, size2 = 0;
npy_int64 x[2*NPY_MAXDIMS+2];
unsigned int nterms;
get_array_memory_extents(a, &start1, &end1, &size1);
get_array_memory_extents(b, &start2, &end2, &size2);
if (!(start1 < end2 && start2 < end1 && start1 < end1 && start2 < end2)) {
/* Memory extents don't overlap */
return MEM_OVERLAP_NO;
}
if (max_work == 0) {
/* Too much work required, give up */
return MEM_OVERLAP_TOO_HARD;
}
/* Convert problem to Diophantine equation form with positive coefficients.
The bounds computed by offset_bounds_from_strides correspond to
all-positive strides.
start1 + sum(abs(stride1)*x1)
== start2 + sum(abs(stride2)*x2)
== end1 - 1 - sum(abs(stride1)*x1')
== end2 - 1 - sum(abs(stride2)*x2')
<=>
sum(abs(stride1)*x1) + sum(abs(stride2)*x2')
== end2 - 1 - start1
OR
sum(abs(stride1)*x1') + sum(abs(stride2)*x2)
== end1 - 1 - start2
We pick the problem with the smaller RHS (they are non-negative due to
the extent check above.)
*/
rhs = MIN(end2 - 1 - start1, end1 - 1 - start2);
if (rhs != (npy_uintp)rhs) {
/* Integer overflow */
return MEM_OVERLAP_OVERFLOW;
}
nterms = 0;
if (strides_to_terms(a, terms, &nterms, 1)) {
return MEM_OVERLAP_OVERFLOW;
}
if (strides_to_terms(b, terms, &nterms, 1)) {
return MEM_OVERLAP_OVERFLOW;
}
if (PyArray_ITEMSIZE(a) > 1) {
terms[nterms].a = 1;
terms[nterms].ub = PyArray_ITEMSIZE(a) - 1;
++nterms;
}
if (PyArray_ITEMSIZE(b) > 1) {
terms[nterms].a = 1;
terms[nterms].ub = PyArray_ITEMSIZE(b) - 1;
++nterms;
}
/* Simplify, if possible */
if (diophantine_simplify(&nterms, terms, rhs)) {
/* Integer overflow */
return MEM_OVERLAP_OVERFLOW;
}
/* Solve */
return solve_diophantine(nterms, terms, rhs, max_work, 0, x);
}
