py: Generalise and reduce code size of array +, += and .extend().

By using the buffer protocol for these array operations, we now allow
addition of memoryview objects, and objects with "incompatible"
typecodes (in this case it just adds bytes naively).  This is an
extension to CPython which seems sensible.  It also reduces the code
size.

py/objarray.c

@@ -229,22 +229,20 @@ STATIC mp_obj_t array_binary_op(mp_uint_t op, mp_obj_t lhs_in, mp_obj_t rhs_in)
     mp_obj_array_t *lhs = lhs_in;
     switch (op) {
         case MP_BINARY_OP_ADD: {
-            #if MICROPY_PY_BUILTINS_MEMORYVIEW
-            if (lhs->base.type == &mp_type_memoryview) {
-                return MP_OBJ_NULL; // op not supported
-            }
-            #endif
-            // if we get here then lhs is not a memoryview, so we don't need to use (& TYPECODE_MASK)
-            if (mp_obj_get_type(rhs_in) != lhs->base.type) {
-                return MP_OBJ_NULL; // op not supported
-            }
-            mp_obj_array_t *rhs = rhs_in;
-            if (lhs->typecode != rhs->typecode) {
-                return MP_OBJ_NULL; // op not supported
-            }
-            int sz = mp_binary_get_size('@', lhs->typecode, NULL);
-            mp_obj_array_t *res = array_new(lhs->typecode, lhs->len + rhs->len);
-            mp_seq_cat((byte*)res->items, lhs->items, lhs->len * sz, rhs->items, rhs->len * sz, byte);
+            // allow to add anything that has the buffer protocol (extension to CPython)
+            mp_buffer_info_t lhs_bufinfo;
+            mp_buffer_info_t rhs_bufinfo;
+            array_get_buffer(lhs_in, &lhs_bufinfo, MP_BUFFER_READ);
+            mp_get_buffer_raise(rhs_in, &rhs_bufinfo, MP_BUFFER_READ);
+
+            int sz = mp_binary_get_size('@', lhs_bufinfo.typecode, NULL);
+
+            // convert byte count to element count (in case rhs is not multiple of sz)
+            mp_uint_t rhs_len = rhs_bufinfo.len / sz;
+
+            // note: lhs->len is element count of lhs, lhs_bufinfo.len is byte count
+            mp_obj_array_t *res = array_new(lhs_bufinfo.typecode, lhs->len + rhs_len);
+            mp_seq_cat((byte*)res->items, lhs_bufinfo.buf, lhs_bufinfo.len, rhs_bufinfo.buf, rhs_len * sz, byte);
             return res;
         }
 
@@ -297,32 +295,27 @@ STATIC mp_obj_t array_extend(mp_obj_t self_in, mp_obj_t arg_in) {
     assert(MP_OBJ_IS_TYPE(self_in, &mp_type_array) || MP_OBJ_IS_TYPE(self_in, &mp_type_bytearray));
     mp_obj_array_t *self = self_in;
 
-    // check for compatible types (array & array, or bytearray & bytearray)
-    if (mp_obj_get_type(arg_in) != self->base.type) {
-    type_error:
-        nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError,
-            "incompatible type for array operation"));
-    }
-
-    // check for compatible typecode
-    mp_obj_array_t *arg = arg_in;
-    if (self->typecode != arg->typecode) {
-        goto type_error;
-    }
+    // allow to extend by anything that has the buffer protocol (extension to CPython)
+    mp_buffer_info_t arg_bufinfo;
+    mp_get_buffer_raise(arg_in, &arg_bufinfo, MP_BUFFER_READ);
 
     int sz = mp_binary_get_size('@', self->typecode, NULL);
 
+    // convert byte count to element count
+    mp_uint_t len = arg_bufinfo.len / sz;
+
     // make sure we have enough room to extend
-    if (self->free < arg->len) {
     // TODO: alloc policy; at the moment we go conservative
-        self->items = m_realloc(self->items, (self->len + self->free) * sz, (self->len + arg->len) * sz);
-        self->free += arg->len;
+    if (self->free < len) {
+        self->items = m_realloc(self->items, (self->len + self->free) * sz, (self->len + len) * sz);
+        self->free = 0;
+    } else {
+        self->free -= len;
     }
 
     // extend
-    mp_seq_copy((byte*)self->items + self->len * sz, arg->items, arg->len * sz, byte);
-    self->len += arg->len;
-    self->free -= arg->len;
+    mp_seq_copy((byte*)self->items + self->len * sz, arg_bufinfo.buf, len * sz, byte);
+    self->len += len;
 
     return mp_const_none;
 }