ENH: Implement axes keyword argument for gufuncs.

The axes argument allows one to specify the axes on which
the gufunc will operate (by default, the trailing ones).
It has to be a list with length equal to the number of
operands, and each element a tuple of length equal to the
number of core dimensions, with each element an axis index.

If there is only one core dimension, the tuple can be
replaced by a single index, and if none of the outputs have
core dimensions, the corresponding empty tuples can be
omitted.

1 files changed, 207 insertions, 16 deletions

diff --git a/numpy/core/src/umath/ufunc_object.c b/numpy/core/src/umath/ufunc_object.c
index c67f60752..1ffecb1a6 100644
--- a/numpy/core/src/umath/ufunc_object.c
+++ b/numpy/core/src/umath/ufunc_object.c
@@ -555,7 +555,8 @@ get_ufunc_arguments(PyUFuncObject *ufunc,
                     PyObject **out_extobj,
                     PyObject **out_typetup,
                     int *out_subok,
-                    PyArrayObject **out_wheremask)
+                    PyArrayObject **out_wheremask,
+                    PyObject **out_axes)
 {
     int i, nargs;
     int nin = ufunc->nin;
@@ -570,6 +571,9 @@ get_ufunc_arguments(PyUFuncObject *ufunc,
 
     *out_extobj = NULL;
     *out_typetup = NULL;
+    if (out_axes != NULL) {
+        *out_axes = NULL;
+    }
     if (out_wheremask != NULL) {
         *out_wheremask = NULL;
     }
@@ -806,6 +810,13 @@ get_ufunc_arguments(PyUFuncObject *ufunc,
             }
 
             switch (str[0]) {
+                case 'a':
+                    /* possible axis argument for generalized ufunc */
+                    if (out_axes != NULL && strcmp(str, "axes") == 0) {
+                        *out_axes = value;
+                        bad_arg = 0;
+                    }
+                    break;
                 case 'c':
                     /* Provides a policy for allowed casting */
                     if (strcmp(str, "casting") == 0) {
@@ -995,6 +1006,10 @@ fail:
     *out_extobj = NULL;
     Py_XDECREF(*out_typetup);
     *out_typetup = NULL;
+    if (out_axes != NULL) {
+        Py_XDECREF(*out_axes);
+        *out_axes = NULL;
+    }
     if (out_wheremask != NULL) {
         Py_XDECREF(*out_wheremask);
         *out_wheremask = NULL;
@@ -1760,6 +1775,155 @@ make_arr_prep_args(npy_intp nin, PyObject *args, PyObject *kwds)
 }
 
 /*
+ * Check whether any of the outputs of a gufunc has core dimensions.
+ */
+static int
+_has_output_coredims(PyUFuncObject *ufunc) {
+    int i;
+    for (i = ufunc->nin; i < ufunc->nin + ufunc->nout; ++i) {
+        if (ufunc->core_num_dims[i] > 0) {
+            return 1;
+        }
+    }
+    return 0;
+}
+
+/*
+ * Interpret a possible axes keyword argument, using it to fill the remap_axis
+ * array which maps default to actual axes for each operand, indexed as
+ * as remap_axis[iop][iaxis]. The default axis order has first all broadcast
+ * axes and then the core axes the gufunc operates on.
+ *
+ * Returns 0 on success, and -1 on failure
+ */
+static int
+_parse_axes_arg(PyUFuncObject *ufunc, PyObject *axes, PyArrayObject **op,
+                int broadcast_ndim, int **remap_axis) {
+    int nin = ufunc->nin;
+    int nout = ufunc->nout;
+    int nop = nin + nout;
+    int iop, list_size;
+
+    if (!PyList_Check(axes)) {
+        PyErr_SetString(PyExc_TypeError, "axes should be a list.");
+        return -1;
+    }
+    list_size = PyList_Size(axes);
+    if (list_size != nop) {
+        if (list_size != nin || _has_output_coredims(ufunc)) {
+            PyErr_Format(PyExc_ValueError,
+                         "axes should be a list with an entry for all "
+                         "%d inputs and outputs; entries for outputs can only "
+                         "be omitted if none of them has core axes.",
+                         nop);
+            return -1;
+        }
+        for (iop = nin; iop < nop; iop++) {
+            remap_axis[iop] = NULL;
+        }
+    }
+    for (iop = 0; iop < list_size; ++iop) {
+        int op_ndim, op_ncore, op_nbroadcast;
+        int have_seen_axis[NPY_MAXDIMS] = {0};
+        PyObject *op_axes_tuple, *axis_item;
+        int axis, op_axis;
+
+        op_ncore = ufunc->core_num_dims[iop];
+        if (op[iop] != NULL) {
+            op_ndim = PyArray_NDIM(op[iop]);
+            op_nbroadcast = op_ndim - op_ncore;
+        }
+        else {
+            op_nbroadcast = broadcast_ndim;
+            op_ndim = broadcast_ndim + op_ncore;
+        }
+        /*
+         * Get axes tuple for operand. If not a tuple already, make it one if
+         * there is only one axis (its content is checked later).
+         */
+        op_axes_tuple = PyList_GET_ITEM(axes, iop);
+        if (PyTuple_Check(op_axes_tuple)) {
+            if (PyTuple_Size(op_axes_tuple) != op_ncore) {
+                if (op_ncore == 1) {
+                    PyErr_Format(PyExc_ValueError,
+                                 "axes item %d should be a tuple with a "
+                                 "single element, or an integer", iop);
+                }
+                else {
+                    PyErr_Format(PyExc_ValueError,
+                                 "axes item %d should be a tuple with %d "
+                                 "elements", iop, op_ncore);
+                }
+                return -1;
+            }
+            Py_INCREF(op_axes_tuple);
+        }
+        else if (op_ncore == 1) {
+            op_axes_tuple = PyTuple_Pack(1, op_axes_tuple);
+            if (op_axes_tuple == NULL) {
+                return -1;
+            }
+        }
+        else {
+            PyErr_Format(PyExc_TypeError, "axes item %d should be a tuple",
+                         iop);
+            return -1;
+        }
+        /*
+         * Now create the remap, starting with the core dimensions, and then
+         * adding the remaining broadcast axes that are to be iterated over.
+         */
+        for (axis = op_nbroadcast; axis < op_ndim; axis++) {
+            axis_item = PyTuple_GET_ITEM(op_axes_tuple, axis - op_nbroadcast);
+            op_axis = PyArray_PyIntAsInt(axis_item);
+            if (error_converting(op_axis) ||
+                    (check_and_adjust_axis(&op_axis, op_ndim) < 0)) {
+                Py_DECREF(op_axes_tuple);
+                return -1;
+            }
+            if (have_seen_axis[op_axis]) {
+                PyErr_Format(PyExc_ValueError,
+                             "axes item %d has value %d repeated",
+                             iop, op_axis);
+                Py_DECREF(op_axes_tuple);
+                return -1;
+            }
+            have_seen_axis[op_axis] = 1;
+            remap_axis[iop][axis] = op_axis;
+        }
+        Py_DECREF(op_axes_tuple);
+        /*
+         * Fill the op_nbroadcast=op_ndim-op_ncore axes not yet set,
+         * using have_seen_axis to skip over entries set above.
+         */
+        for (axis = 0, op_axis = 0; axis < op_nbroadcast; axis++) {
+            while (have_seen_axis[op_axis]) {
+                op_axis++;
+            }
+            remap_axis[iop][axis] = op_axis++;
+        }
+        /*
+         * Check whether we are actually remapping anything. Here,
+         * op_axis can only equal axis if all broadcast axes were the same
+         * (i.e., the while loop above was never entered).
+         */
+        if (axis == op_axis) {
+            while (axis < op_ndim && remap_axis[iop][axis] == axis) {
+                axis++;
+            }
+        }
+        if (axis == op_ndim) {
+            remap_axis[iop] = NULL;
+        }
+    } /* end of for(iop) loop over operands */
+    return 0;
+}
+
+#define REMAP_AXIS(iop, axis) ((remap_axis != NULL && \
+                                remap_axis[iop] != NULL)? \
+                               remap_axis[iop][axis] : axis)
+
+/*
  * Validate the core dimensions of all the operands, and collect all of
  * the labelled core dimensions into 'core_dim_sizes'.
  *
@@ -1781,7 +1945,7 @@ make_arr_prep_args(npy_intp nin, PyObject *args, PyObject *kwds)
  */
 static int
 _get_coredim_sizes(PyUFuncObject *ufunc, PyArrayObject **op,
-                   npy_intp* core_dim_sizes) {
+                   npy_intp* core_dim_sizes, int **remap_axis) {
     int i;
     int nin = ufunc->nin;
     int nout = ufunc->nout;
@@ -1815,8 +1979,8 @@ _get_coredim_sizes(PyUFuncObject *ufunc, PyArrayObject **op,
              */
             for (idim = 0; idim < num_dims; ++idim) {
                 int core_dim_index = ufunc->core_dim_ixs[dim_offset+idim];
-                npy_intp op_dim_size =
-                            PyArray_DIM(op[i], core_start_dim+idim);
+                npy_intp op_dim_size = PyArray_DIM(
+                    op[i], REMAP_AXIS(i, core_start_dim+idim));
 
                 if (core_dim_sizes[core_dim_index] == -1) {
                     core_dim_sizes[core_dim_index] = op_dim_size;
@@ -1950,7 +2114,9 @@ PyUFunc_GeneralizedFunction(PyUFuncObject *ufunc,
     /* The sizes of the core dimensions (# entries is ufunc->core_num_dim_ix) */
     npy_intp *core_dim_sizes = inner_dimensions + 1;
     int core_dim_ixs_size;
-
+    /* swapping around of axes */
+    int *remap_axis_memory = NULL;
+    int **remap_axis = NULL;
     /* The __array_prepare__ function to call for each output */
     PyObject *arr_prep[NPY_MAXARGS];
     /*
@@ -1962,8 +2128,8 @@ PyUFunc_GeneralizedFunction(PyUFuncObject *ufunc,
     NPY_ORDER order = NPY_KEEPORDER;
     /* Use the default assignment casting rule */
     NPY_CASTING casting = NPY_DEFAULT_ASSIGN_CASTING;
-    /* When provided, extobj and typetup contain borrowed references */
-    PyObject *extobj = NULL, *type_tup = NULL;
+    /* When provided, extobj, typetup, and axes contain borrowed references */
+    PyObject *extobj = NULL, *type_tup = NULL, *axes = NULL;
 
     if (ufunc == NULL) {
         PyErr_SetString(PyExc_ValueError, "function not supported");
@@ -1990,7 +2156,7 @@ PyUFunc_GeneralizedFunction(PyUFuncObject *ufunc,
     /* Get all the arguments */
     retval = get_ufunc_arguments(ufunc, args, kwds,
                 op, &order, &casting, &extobj,
-                &type_tup, &subok, NULL);
+                &type_tup, &subok, NULL, &axes);
     if (retval < 0) {
         goto fail;
     }
@@ -2026,8 +2192,30 @@ PyUFunc_GeneralizedFunction(PyUFuncObject *ufunc,
         goto fail;
     }
 
+    /* Possibly remap axes. */
+    if (axes) {
+        /*
+         * possibly remap axes, using newly allocated memory.
+         */
+        remap_axis = PyArray_malloc(sizeof(remap_axis[0]) * nop);
+        remap_axis_memory = PyArray_malloc(sizeof(remap_axis_memory[0]) *
+                                                  nop * NPY_MAXDIMS);
+        if (remap_axis == NULL || remap_axis_memory == NULL) {
+            PyErr_NoMemory();
+            goto fail;
+        }
+        for (i=0; i < nop; i++) {
+            remap_axis[i] = remap_axis_memory + i * NPY_MAXDIMS;
+        }
+        retval = _parse_axes_arg(ufunc, axes, op, broadcast_ndim,
+                                 remap_axis);
+        if(retval < 0) {
+            goto fail;
+        }
+    } /* end of if(axis) */
+
     /* Collect the lengths of the labelled core dimensions */
-    retval = _get_coredim_sizes(ufunc, op, core_dim_sizes);
+    retval = _get_coredim_sizes(ufunc, op, core_dim_sizes, remap_axis);
     if(retval < 0) {
         goto fail;
     }
@@ -2054,7 +2242,8 @@ PyUFunc_GeneralizedFunction(PyUFuncObject *ufunc,
         /* Broadcast all the unspecified dimensions normally */
         for (idim = 0; idim < broadcast_ndim; ++idim) {
             if (idim >= broadcast_ndim - n) {
-                op_axes_arrays[i][idim] = idim - (broadcast_ndim - n);
+                op_axes_arrays[i][idim] =
+                    REMAP_AXIS(i, idim - (broadcast_ndim - n));
             }
             else {
                 op_axes_arrays[i][idim] = -1;
@@ -2074,7 +2263,7 @@ PyUFunc_GeneralizedFunction(PyUFuncObject *ufunc,
             for (idim = 0; idim < num_dims; ++idim) {
                 iter_shape[j] = core_dim_sizes[
                                         ufunc->core_dim_ixs[dim_offset + idim]];
-                op_axes_arrays[i][j] = n + idim;
+                op_axes_arrays[i][j] = REMAP_AXIS(i, n + idim);
                 ++j;
             }
         }
@@ -2220,11 +2409,12 @@ PyUFunc_GeneralizedFunction(PyUFuncObject *ufunc,
         for (j = 0; j < num_dims; ++j) {
             if (core_start_dim + j >= 0) {
                 /*
-                 * Force the stride to zero when the shape is 1, sot
+                 * Force the stride to zero when the shape is 1, so
                  * that the broadcasting works right.
                  */
-                if (shape[core_start_dim + j] != 1) {
-                    inner_strides[idim++] = strides[core_start_dim + j];
+                int remapped_axis = REMAP_AXIS(i, core_start_dim + j);
+                if (shape[remapped_axis] != 1) {
+                    inner_strides[idim++] = strides[remapped_axis];
                 } else {
                     inner_strides[idim++] = 0;
                 }
@@ -2375,7 +2565,8 @@ fail:
     }
     Py_XDECREF(type_tup);
     Py_XDECREF(arr_prep_args);
-
+    PyArray_free(remap_axis_memory);
+    PyArray_free(remap_axis);
     return retval;
 }
 
@@ -2450,7 +2641,7 @@ PyUFunc_GenericFunction(PyUFuncObject *ufunc,
     /* Get all the arguments */
     retval = get_ufunc_arguments(ufunc, args, kwds,
                 op, &order, &casting, &extobj,
-                &type_tup, &subok, &wheremask);
+                &type_tup, &subok, &wheremask, NULL);
     if (retval < 0) {
         goto fail;
     }