py: Add casting to viper; add native mem stores to viper.

Viper can now do the following:

def store(p:ptr8, c:int):
    p[0] = c

This does a store of c to the memory pointed to by p using a machine
instructions inline in the code.

py/nativeglue.c

@@ -51,8 +51,16 @@ mp_uint_t mp_convert_obj_to_native(mp_obj_t obj, mp_uint_t type) {
     switch (type & 3) {
         case MP_NATIVE_TYPE_OBJ: return (mp_uint_t)obj;
         case MP_NATIVE_TYPE_BOOL:
-        case MP_NATIVE_TYPE_INT:
-        case MP_NATIVE_TYPE_UINT: return mp_obj_get_int(obj);
+        case MP_NATIVE_TYPE_INT: return mp_obj_get_int(obj);
+        case MP_NATIVE_TYPE_UINT: {
+            mp_buffer_info_t bufinfo;
+            if (mp_get_buffer(obj, &bufinfo, MP_BUFFER_RW)) {
+                return (mp_uint_t)bufinfo.buf;
+            } else {
+                // TODO should be mp_obj_get_uint_truncated or something
+                return mp_obj_get_int(obj);
+            }
+        }
         default: assert(0); return 0;
     }
 }

py/qstrdefs.h

@@ -77,6 +77,9 @@ Q(const)
 Q(native)
 Q(viper)
 Q(uint)
+Q(ptr)
+Q(ptr8)
+Q(ptr16)
 #endif
 
 #if MICROPY_EMIT_INLINE_THUMB

tests/micropython/viper_ptr8_store.py

+# test ptr8 type
+
+@micropython.viper
+def set(dest:ptr8, val:int):
+    dest[0] = val
+
+@micropython.viper
+def memset(dest:ptr8, val:int, n:int):
+    for i in range(n):
+        dest[i] = val
+
+@micropython.viper
+def memset2(dest_in, val:int):
+    dest = ptr8(dest_in)
+    n = int(len(dest_in))
+    for i in range(n):
+        dest[i] = val
+
+b = bytearray(4)
+print(b)
+
+set(b, 42)
+print(b)
+
+memset(b, 43, len(b))
+print(b)
+
+memset2(b, 44)
+print(b)

tests/micropython/viper_ptr8_store.py.exp

+bytearray(b'\x00\x00\x00\x00')
+bytearray(b'*\x00\x00\x00')
+bytearray(b'++++')
+bytearray(b',,,,')