more custom mutator remodelling

examples/custom_mutators/custom_mutator_helpers.h

@@ -5,8 +5,18 @@
 #include "types.h"
 #include <stdlib.h>
 
+#define INITIAL_GROWTH_SIZE (64)
+
 #define RAND_BELOW(limit) (rand() % (limit))
 
+/* Use in a struct: creates a name_buf and a name_size variable. */
+#define BUF_VAR(type, name) \
+  type * name##_buf;        \
+  size_t name##_size;
+/* this filles in `&structptr->something_buf, &structptr->something_size`. */
+#define BUF_PARAMS(struct, name) \
+  (void **)&struct->name##_buf, &struct->name##_size
+
 typedef struct {
 
 } afl_t;
@@ -267,5 +277,56 @@ static void surgical_havoc_mutate(u8 *out_buf, s32 begin, s32 end) {
 
 }
 
+/* This function makes sure *size is > size_needed after call.
+ It changes buf and size in-place, if needed.
+ It will realloc *buf otherwise.
+ *size will grow exponentially as per:
+ https://blog.mozilla.org/nnethercote/2014/11/04/please-grow-your-buffers-exponentially/
+ Will return NULL if size_needed is <1 or *size is negative or malloc Failed.
+ @return For convenience, this function returns *buf. NULL on error.
+ */
+static inline void *maybe_grow(void **buf, size_t *size, size_t size_needed) {
+
+  /* Oops. found a bug? */
+  if (unlikely(size_needed < 1)) return NULL;
+
+  /* No need to realloc */
+  if (likely(*size >= size_needed)) return *buf;
+  if (unlikely(*size < 0)) return NULL;
+  /* No inital size was set */
+  if (*size == 0) *size = INITIAL_GROWTH_SIZE;
+  while (*size < size_needed) {
+
+    *size *= 2;
+    if ((*size) < 0) {
+
+      /* An overflow occurred. Fall back to size_needed */
+      *size = size_needed;
+
+    }
+
+  }
+
+  *buf = realloc(*buf, *size);
+
+  return *buf;
+
+}
+
+/* Swaps buf1 ptr and buf2 ptr, as well as their sizes */
+static inline void swap_bufs(void **buf1, size_t *size1, void **buf2,
+                             size_t *size2) {
+
+  void * scratch_buf = *buf1;
+  size_t scratch_size = *size1;
+  *buf1 = *buf2;
+  *size1 = *size2;
+  *buf2 = scratch_buf;
+  *size2 = scratch_size;
+
+}
+
+#undef INITIAL_GROWTH_SIZE
+
 #endif