ffi: Implement ffivar.get()/set() methods.

Done by introducing another factored out helper API in binary.c. This API
can be reused also by array and struct modules.
diff --git a/py/binary.c b/py/binary.c
new file mode 100644
index 0000000..a738dd6
--- /dev/null
+++ b/py/binary.c
@@ -0,0 +1,96 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <assert.h>
+
+#include "misc.h"
+#include "mpconfig.h"
+#include "qstr.h"
+#include "obj.h"
+#include "objint.h"
+#include "binary.h"
+
+// Helpers to work with binary-encoded data
+
+mp_obj_t mp_binary_get_val(char typecode, void *p, int index) {
+    int val = 0;
+    switch (typecode) {
+        case 'b':
+            val = ((int8_t*)p)[index];
+            break;
+        case BYTEARRAY_TYPECODE:
+        case 'B':
+            val = ((uint8_t*)p)[index];
+            break;
+        case 'h':
+            val = ((int16_t*)p)[index];
+            break;
+        case 'H':
+            val = ((uint16_t*)p)[index];
+            break;
+        case 'i':
+        case 'l':
+            return mp_obj_new_int(((int32_t*)p)[index]);
+        case 'I':
+        case 'L':
+            return mp_obj_new_int_from_uint(((uint32_t*)p)[index]);
+#if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
+        case 'q':
+        case 'Q':
+            // TODO: Explode API more to cover signedness
+            return mp_obj_new_int_from_ll(((long long*)p)[index]);
+#endif
+#if MICROPY_ENABLE_FLOAT
+        case 'f':
+            return mp_obj_new_float(((float*)p)[index]);
+        case 'd':
+            return mp_obj_new_float(((double*)p)[index]);
+#endif
+    }
+    return MP_OBJ_NEW_SMALL_INT(val);
+}
+
+void mp_binary_set_val(char typecode, void *p, int index, mp_obj_t val_in) {
+    machine_int_t val = 0;
+    if (MP_OBJ_IS_INT(val_in)) {
+        val = mp_obj_int_get(val_in);
+    }
+
+    switch (typecode) {
+        case 'b':
+            ((int8_t*)p)[index] = val;
+            break;
+        case BYTEARRAY_TYPECODE:
+        case 'B':
+            val = ((uint8_t*)p)[index] = val;
+            break;
+        case 'h':
+            val = ((int16_t*)p)[index] = val;
+            break;
+        case 'H':
+            val = ((uint16_t*)p)[index] = val;
+            break;
+        case 'i':
+        case 'l':
+            ((int32_t*)p)[index] = val;
+            break;
+        case 'I':
+        case 'L':
+            ((uint32_t*)p)[index] = val;
+            break;
+#if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
+        case 'q':
+        case 'Q':
+            assert(0);
+            ((long long*)p)[index] = val;
+            break;
+#endif
+#if MICROPY_ENABLE_FLOAT
+        case 'f':
+            ((float*)p)[index] = mp_obj_float_get(val_in);
+            break;
+        case 'd':
+            ((double*)p)[index] = mp_obj_float_get(val_in);
+            break;
+#endif
+    }
+}
diff --git a/py/binary.h b/py/binary.h
new file mode 100644
index 0000000..0bd6ad1
--- /dev/null
+++ b/py/binary.h
@@ -0,0 +1,7 @@
+// Use special typecode to differentiate repr() of bytearray vs array.array('B')
+// (underlyingly they're same).
+#define BYTEARRAY_TYPECODE 0
+
+int mp_binary_get_size(char typecode);
+mp_obj_t mp_binary_get_val(char typecode, void *p, int index);
+void mp_binary_set_val(char typecode, void *p, int index, mp_obj_t val_in);
diff --git a/py/objint.h b/py/objint.h
index 6662be1..df3b81b 100644
--- a/py/objint.h
+++ b/py/objint.h
@@ -8,3 +8,7 @@
 void int_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t self_in, mp_print_kind_t kind);
 mp_obj_t int_unary_op(int op, mp_obj_t o_in);
 mp_obj_t int_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in);
+
+#if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
+mp_obj_t mp_obj_new_int_from_ll(long long val);
+#endif
diff --git a/py/objint_longlong.c b/py/objint_longlong.c
index f637807..7412cc0 100644
--- a/py/objint_longlong.c
+++ b/py/objint_longlong.c
@@ -13,8 +13,6 @@
 
 #if MICROPY_LONGINT_IMPL == MICROPY_LONGINT_IMPL_LONGLONG
 
-STATIC mp_obj_t mp_obj_new_int_from_ll(long long val);
-
 // Python3 no longer has "l" suffix for long ints. We allow to use it
 // for debugging purpose though.
 #ifdef DEBUG
diff --git a/py/py.mk b/py/py.mk
index e29d7b6..1d9eb53 100644
--- a/py/py.mk
+++ b/py/py.mk
@@ -63,6 +63,7 @@
 	objzip.o \
 	sequence.o \
 	stream.o \
+	binary.o \
 	builtin.o \
 	builtinimport.o \
 	builtinevex.o \