feat: unsigned add checks

src/liberror/public.h

@@ -1,7 +1,7 @@
 #ifndef CWARE_LIBERROR_PUBLIC_H
 #define CWARE_LIBERROR_PUBLIC_H
 
-#if !defined(LIBERROR_NO_SAFETY_CHECKS)
+#ifndef LIBERROR_NO_SAFETY_CHECKS
 #define LIBERROR_ASSERT(expression, type, message, function)                                  \
     do {                                                                                      \
         if((expression) != 0) {                                                               \
@@ -15,10 +15,35 @@
 #define LIBERROR_TEST(expression, message) \
     LIBERROR_ASSERT(expression, "ASSERTION", message, "main")
 
+#define LIBERROR_UNSIGNED_ADD_CHECK(a, b, type, message, function)          \
+    do {                                                                    \
+        /* a + b, where either a or b are zero, can never overflow. */      \
+        if(((a) == 0) || ((b) == 0)) {                                      \
+            break;                                                          \
+        }                                                                   \
+                                                                            \
+        if((a) > (b)) {                                                     \
+            /* a + b is greater or equal to a, so there was no overflow. */ \
+            if(((a) + (b)) >= (a)) {                                        \
+                break;                                                      \
+            }                                                               \
+                                                                            \
+            LIBERROR_ASSERT(1 == 0, type, message, function);               \
+        } else if((a) <= (b)) {                                             \
+            /* a + b is greater or equal to b, so there was no overflow. */ \
+            if(((a) + (b)) >= (b)) {                                        \
+                break;                                                      \
+            }                                                               \
+                                                                            \
+            LIBERROR_ASSERT(1 == 0, type, message, function);
+    } while(0)
+
 #else
 
 #define LIBERROR_ASSERT(expression, message)
 #define LIBERROR_TEST(expression, type, message, function)
+#define LIBERROR_UNSIGNED_ADD_CHECk(a, b, type, message, function)
+
 #endif
 
 #endif