From 55bc5a0d99c1118c6842d42e958c000ed696706c Mon Sep 17 00:00:00 2001
From: Alexander Orzechowski <orzechowski.alexander@gmail.com>
Date: Thu, 25 Aug 2022 21:55:46 -0400
Subject: [PATCH] util/array: Add reverse helpers

---
 include/util/array.h | 11 +++++++++++
 util/array.c         | 23 +++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/include/util/array.h b/include/util/array.h
index a51bdb640..862921680 100644
--- a/include/util/array.h
+++ b/include/util/array.h
@@ -15,4 +15,15 @@ void array_remove_at(struct wl_array *arr, size_t offset, size_t size);
  */
 bool array_realloc(struct wl_array *arr, size_t size);
 
+/**
+ * Returns a pointer to the first valid element in a reversed array.
+ */
+void *array_reversed_start(struct wl_array *arr);
+
+/**
+ * Adds a new element to the array inserting them starting from a higher
+ * memory address effectively inserting them in reverse order.
+ */
+void *array_reversed_add(struct wl_array *arr, size_t size);
+
 #endif
diff --git a/util/array.c b/util/array.c
index ec16a7b13..427cf725a 100644
--- a/util/array.c
+++ b/util/array.c
@@ -38,3 +38,26 @@ bool array_realloc(struct wl_array *arr, size_t size) {
 	arr->alloc = alloc;
 	return true;
 }
+
+void *array_reversed_start(struct wl_array *arr) {
+	char *data = arr->data;
+	return data + arr->alloc - arr->size;
+}
+
+void *array_reversed_add(struct wl_array *arr, size_t size) {
+	if (arr->size + size > arr->alloc) {
+		size_t new_alloc = arr->alloc * 2;
+		char *new = malloc(new_alloc);
+		if (!new) {
+			return NULL;
+		}
+
+		memcpy(new + (new_alloc - arr->size), array_reversed_start(arr), arr->size);
+		free(arr->data);
+		arr->data = new;
+		arr->alloc = new_alloc;
+	}
+
+	arr->size += size;
+	return array_reversed_start(arr);
+}