ndarray: Fix memoryview(ulab.array(...))

For now this only handles the 1D case.  In theory it would work for
any dense array, however, I found that ndarray_is_dense didn't behave
for me so I implemented this instead.

Add a test.  Before the change, this test would segfault.

Closes #328.

Author: jepler

code/ndarray.c

@@ -1986,8 +1986,15 @@ mp_obj_t ndarray_info(mp_obj_t obj_in) {
 MP_DEFINE_CONST_FUN_OBJ_1(ndarray_info_obj, ndarray_info);
 #endif
 
+// (the get_buffer protocol returns 0 for success, 1 for failure)
 mp_int_t ndarray_get_buffer(mp_obj_t self_in, mp_buffer_info_t *bufinfo, mp_uint_t flags) {
     ndarray_obj_t *self = MP_OBJ_TO_PTR(self_in);
-    // buffer_p.get_buffer() returns zero for success, while mp_get_buffer returns true for success
-    return !mp_get_buffer(self->array, bufinfo, flags);
+    if (self->ndim != 1 || self->strides[0] > 1) {
+        // For now, only allow fetching buffer of a 1d-array
+        return 1;
+    }
+    bufinfo->len = self->itemsize * self->len;
+    bufinfo->buf = self->array;
+    bufinfo->typecode = self->dtype;
+    return 0;
 }

tests/common/buffer.py

@@ -0,0 +1,16 @@
+try:
+    import ulab as np
+except:
+    import numpy as np
+
+def print_as_buffer(a):
+    print(len(memoryview(a)), list(memoryview(a)))
+print_as_buffer(np.ones(3))
+print_as_buffer(np.zeros(3))
+print_as_buffer(np.ones(1, dtype=np.int8))
+print_as_buffer(np.ones(2, dtype=np.uint8))
+print_as_buffer(np.ones(3, dtype=np.int16))
+print_as_buffer(np.ones(4, dtype=np.uint16))
+print_as_buffer(np.ones(5, dtype=np.float))
+print_as_buffer(np.linspace(0, 1, 9))
+

tests/common/buffer.py.exp

@@ -0,0 +1,8 @@
+3 [1.0, 1.0, 1.0]
+3 [0.0, 0.0, 0.0]
+1 [1]
+2 [1, 1]
+3 [1, 1, 1]
+4 [1, 1, 1, 1]
+5 [1.0, 1.0, 1.0, 1.0, 1.0]
+9 [0.0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1.0]