diff options
Diffstat (limited to 'doc/source/reference/c-api.iterator.rst')
| -rw-r--r-- | doc/source/reference/c-api.iterator.rst | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/doc/source/reference/c-api.iterator.rst b/doc/source/reference/c-api.iterator.rst index b38c21390..b5d00f4be 100644 --- a/doc/source/reference/c-api.iterator.rst +++ b/doc/source/reference/c-api.iterator.rst @@ -461,6 +461,33 @@ Construction and Destruction Then, call :c:func:`NpyIter_Reset` to allocate and fill the buffers with their initial values. + .. c:var:: NPY_ITER_COPY_IF_OVERLAP + + If a write operand has overlap with a read operand, eliminate all + overlap by making temporary copies (with UPDATEIFCOPY for write + operands). + + Overlapping means: + + - For a (read, write) pair of operands, there is a memory address + that contains data common to both arrays, which can be reached + via *different* index/dtype/shape combinations. + + - In particular, unless the arrays have the same shape, dtype, + strides, and start address, any shared common data byte accessible + by indexing implies overlap. + + Because exact overlap detection has exponential runtime + in the number of dimensions, the decision is made based + on heuristics, which has false positives (needless copies in unusual + cases) but has no false negatives. + + If read/write overlap exists and write operands are modified in the + iterator loop element-wise, this flag ensures the result of the + operation is the same as if all operands were copied. + In cases where copies would need to be made, **the result of the + computation may be undefined without this flag!** + Flags that may be passed in ``op_flags[i]``, where ``0 <= i < nop``: .. c:var:: NPY_ITER_READWRITE |