member_offset_bits: express member offset in bits instead of bytes

src/analyses/goto_rw.cpp

@@ -221,12 +221,12 @@ void rw_range_sett::get_objects_member(
 
   const struct_typet &struct_type=to_struct_type(type);
 
-  // TODO - assumes members are byte-aligned
   range_spect offset=
-    to_range_spect(member_offset(
+    to_range_spect(
+      member_offset_bits(
         struct_type,
         expr.get_component_name(),
-        ns) * 8);
+        ns));
 
   if(offset!=-1)
     offset+=range_start;

src/util/pointer_offset_size.cpp

@@ -80,6 +80,29 @@ mp_integer member_offset(
   return offsets->second;
 }
 
+mp_integer member_offset_bits(
+  const struct_typet &type,
+  const irep_idt &member,
+  const namespacet &ns)
+{
+  mp_integer offset=0;
+  const struct_typet::componentst &components=type.components();
+
+  for(const auto &comp : components)
+  {
+    if(comp.get_name()==member)
+      break;
+
+    mp_integer member_bits=pointer_offset_bits(comp.type(), ns);
+    if(member_bits==-1)
+      return member_bits;
+
+    offset+=member_bits;
+  }
+
+  return offset;
+}
+
 mp_integer pointer_offset_size(
   const typet &type,
   const namespacet &ns)

src/util/pointer_offset_size.h

@@ -45,6 +45,11 @@ mp_integer member_offset(
   const irep_idt &member,
   const namespacet &ns);
 
+mp_integer member_offset_bits(
+  const struct_typet &type,
+  const irep_idt &member,
+  const namespacet &ns);
+
 mp_integer pointer_offset_size(
   const typet &type,
   const namespacet &ns);