bootutil: Provide flash_area_to_image

The flash_area_id_to_image has been replaced with flash_area_to_image
that moves flash_area_get_id inside the flash_area_id_to_image
and changes the logic so that it is now independent from
image numbers and should not require updates when BOOT_IMAGE_NUMBER
gets increased.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>

boot/bootutil/src/bootutil_public.c

@@ -458,18 +458,18 @@ boot_swap_type_multi(int image_index)
     return BOOT_SWAP_TYPE_NONE;
 }
 
-static int flash_area_id_to_image(int id)
+static int flash_area_to_image(const struct flash_area *fa)
 {
-#if BOOT_IMAGE_NUMBER > 2
-#error "BOOT_IMAGE_NUMBER > 2 requires change to flash_area_id_to_image"
-#elif BOOT_IMAGE_NUMBER > 1
-    if (FLASH_AREA_IMAGE_PRIMARY(1) == id || (FLASH_AREA_IMAGE_SECONDARY(1) == id)) {
-        return 1;
+    int i = 0;
+    int id = flash_area_get_id(fa);
+
+    while (BOOT_IMAGE_NUMBER > 1 && i < BOOT_IMAGE_NUMBER) {
+        if (FLASH_AREA_IMAGE_PRIMARY(i) == id || (FLASH_AREA_IMAGE_SECONDARY(i) == id)) {
+            break;
+        }
+        ++i;
     }
-#else
-    (void)id;
-#endif
-    return 0;
+    return i;
 }
 
 int
@@ -517,8 +517,7 @@ boot_set_next(const struct flash_area *fa, bool active, bool confirm)
                 } else {
                     swap_type = BOOT_SWAP_TYPE_TEST;
                 }
-                rc = boot_write_swap_info(fa, swap_type,
-                                          flash_area_id_to_image(flash_area_get_id(fa)));
+                rc = boot_write_swap_info(fa, swap_type, flash_area_to_image(fa));
             }
         }
         break;