modstruct: Fix .calcsize() to account for struct type/alignment.

py/binary.c

 #include <stdint.h>
+#include <stdlib.h>
 #include <assert.h>
 
 #include "misc.h"
@@ -9,34 +10,52 @@
 
 // Helpers to work with binary-encoded data
 
-int mp_binary_get_size(char typecode) {
-    // This assumes that unsigned and signed types are of the same type,
-    // which is invariant for [u]intN_t.
-    switch (typecode) {
+int mp_binary_get_size(char struct_type, char val_type, uint *palign) {
+    int size = 0;
+    int align = 1;
+    switch (struct_type) {
+        case '<': case '>':
+            switch (val_type) {
+                case 'b': case 'B':
+                    size = 1; break;
+                case 'h': case 'H':
+                    size = 2; break;
+                case 'i': case 'I':
+                    size = 4; break;
+                case 'l': case 'L':
+                    size = 4; break;
+                case 'q': case 'Q':
+                    size = 8; break;
+            }
+            break;
+        case '@': {
+            // TODO:
+            // The simplest heuristic for alignment is to align by value
+            // size, but that doesn't work for "bigger than int" types,
+            // for example, long long may very well have long alignment
+            // So, we introduce separate alignment handling, but having
+            // formal support for that is different from actually supporting
+            // particular (or any) ABI.
+            switch (val_type) {
                 case BYTEARRAY_TYPECODE:
-        case 'b':
-        case 'B':
-            return sizeof(int8_t);
-        case 'h':
-        case 'H':
-            return sizeof(int16_t);
-        case 'i':
-        case 'I':
-            return sizeof(int32_t);
-        case 'l':
-        case 'L':
-            return sizeof(int32_t);
-        case 'q':
-        case 'Q':
-            return sizeof(long long);
-#if MICROPY_ENABLE_FLOAT
-        case 'f':
-            return sizeof(float);
-        case 'd':
-            return sizeof(double);
-#endif
+                case 'b': case 'B':
+                    align = size = 1; break;
+                case 'h': case 'H':
+                    align = size = sizeof(short); break;
+                case 'i': case 'I':
+                    align = size = sizeof(int); break;
+                case 'l': case 'L':
+                    align = size = sizeof(long); break;
+                case 'q': case 'Q':
+                    // TODO: This is for x86
+                    align = sizeof(int); size = sizeof(long long); break;
+            }
+        }
     }
-    return -1;
+    if (palign != NULL) {
+        *palign = align;
+    }
+    return size;
 }
 
 mp_obj_t mp_binary_get_val_array(char typecode, void *p, int index) {
@@ -80,44 +99,10 @@ mp_obj_t mp_binary_get_val_array(char typecode, void *p, int index) {
 #define is_signed(typecode) (typecode > 'Z')
 mp_obj_t mp_binary_get_val(char struct_type, char val_type, byte **ptr) {
     byte *p = *ptr;
-    uint size = 0;
-    switch (struct_type) {
-        case '<': case '>':
-            switch (val_type) {
-                case 'b': case 'B':
-                    size = 1; break;
-                case 'h': case 'H':
-                    size = 2; break;
-                case 'i': case 'I':
-                    size = 4; break;
-                case 'l': case 'L':
-                    size = 4; break;
-                case 'q': case 'Q':
-                    size = 8; break;
-            }
-            break;
-        case '@': {
-            // TODO:
-            // The simplest heuristic for alignment is to align by value
-            // size, but that doesn't work for "bigger than int" types,
-            // for example, long long may very well have long alignment
-            // So, we introduce separate alignment handling, but having
-            // formal support for that is different from actually supporting
-            // particular (or any) ABI.
-            uint align = 0;
-            switch (val_type) {
-                case 'b': case 'B':
-                    align = size = 1; break;
-                case 'h': case 'H':
-                    align = size = sizeof(short); break;
-                case 'i': case 'I':
-                    align = size = sizeof(int); break;
-                case 'l': case 'L':
-                    align = size = sizeof(long); break;
-                case 'q': case 'Q':
-                    // TODO: This is for x86
-                    align = sizeof(int); size = sizeof(long long); break;
-            }
+    uint align;
+
+    int size = mp_binary_get_size(struct_type, val_type, &align);
+    if (struct_type == '@') {
         // Make pointer aligned
         p = (byte*)(((machine_uint_t)p + align - 1) & ~(align - 1));
         #if MP_ENDIANNESS_LITTLE
@@ -125,8 +110,6 @@ mp_obj_t mp_binary_get_val(char struct_type, char val_type, byte **ptr) {
         #else
         struct_type = '>';
         #endif
-            break;
-        }
     }
 
     int delta;

py/binary.h

@@ -2,7 +2,7 @@
 // (underlyingly they're same).
 #define BYTEARRAY_TYPECODE 0
 
-int mp_binary_get_size(char typecode);
+int mp_binary_get_size(char struct_type, char val_type, uint *palign);
 mp_obj_t mp_binary_get_val_array(char typecode, void *p, int index);
 mp_obj_t mp_binary_get_val(char struct_type, char val_type, byte **ptr);
 void mp_binary_set_val_array(char typecode, void *p, int index, mp_obj_t val_in);

py/modstruct.c

@@ -37,12 +37,14 @@ STATIC uint calcsize_items(const char *fmt) {
 STATIC mp_obj_t struct_calcsize(mp_obj_t fmt_in) {
     const char *fmt = mp_obj_str_get_str(fmt_in);
     char fmt_type = get_fmt_type(&fmt);
-    (void)fmt_type;
     machine_uint_t size;
     for (size = 0; *fmt; fmt++) {
-        int sz = mp_binary_get_size(*fmt);
+        uint align;
+        int sz = mp_binary_get_size(fmt_type, *fmt, &align);
         // TODO
         assert(sz != -1);
+        // Apply alignment
+        size = (size + align - 1) & ~(align - 1);
         size += sz;
     }
     return MP_OBJ_NEW_SMALL_INT(size);

py/objarray.c

@@ -121,7 +121,7 @@ STATIC mp_obj_t array_append(mp_obj_t self_in, mp_obj_t arg) {
     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;
     if (self->free == 0) {
-        int item_sz = mp_binary_get_size(self->typecode);
+        int item_sz = mp_binary_get_size('@', self->typecode, NULL);
         // TODO: alloc policy
         self->free = 8;
         self->items = m_realloc(self->items,  item_sz * self->len, item_sz * (self->len + self->free));
@@ -154,7 +154,7 @@ STATIC mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
 STATIC machine_int_t array_get_buffer(mp_obj_t o_in, mp_buffer_info_t *bufinfo, int flags) {
     mp_obj_array_t *o = o_in;
     bufinfo->buf = o->items;
-    bufinfo->len = o->len * mp_binary_get_size(o->typecode);
+    bufinfo->len = o->len * mp_binary_get_size('@', o->typecode, NULL);
     bufinfo->typecode = o->typecode;
     return 0;
 }
@@ -190,7 +190,7 @@ const mp_obj_type_t mp_type_bytearray = {
 };
 
 STATIC mp_obj_array_t *array_new(char typecode, uint n) {
-    int typecode_size = mp_binary_get_size(typecode);
+    int typecode_size = mp_binary_get_size('@', typecode, NULL);
     if (typecode_size <= 0) {
         nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "bad typecode"));
     }