Import of the watch repository from Pebble

src/libutil/includes/util/circular_cache.h

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+/*
+ * Copyright 2024 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include "util/order.h"
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+//! @note Needs to handle NULL items gracefully
+typedef void (*CircularCacheItemDestructor)(void *item);
+
+//! Array-backed circular cache
+typedef struct {
+  uint8_t* cache; //<! Pointer to the array
+  size_t item_size; //<! Size of the array element in bytes
+  int next_erased_item_idx; //<! Next array element to be deleted
+  int total_items;
+  Comparator compare_cb;
+  CircularCacheItemDestructor item_destructor;
+} CircularCache;
+
+void circular_cache_init(CircularCache* c, uint8_t* buffer, size_t item_size,
+    int total_items, Comparator compare_cb);
+
+//! Add a destructor to be called when an item is evicted from the circular cache.
+//! @note the destructor needs to handle NULL items gracefully
+void circular_cache_set_item_destructor(CircularCache *c, CircularCacheItemDestructor destructor);
+
+//! @return True if the cache contains the data
+//! @note Item must be of size item_size
+bool circular_cache_contains(CircularCache* c, void* item);
+
+//! @return Pointer to buffer of entry in cache that contains the data
+//! @note Item must be of size item_size
+void *circular_cache_get(CircularCache* c, void* theirs);
+
+//! Push data of size item_size into the circular cache
+//! Overwrites the item at next_erased_item_idx
+void circular_cache_push(CircularCache* c, void* item);
+
+//! Fills a circular cache with the representation an item, useful for non-zero clearing a cache
+//! @note this will assert if an item destructor is set
+void circular_cache_fill(CircularCache *c, uint8_t *item);
+
+//! Flushes the buffer, calling destructors for each item in the cache. The calling module must
+//! be able to differentiate between a valid and invalid entry in the cache (e.g. the cache is not
+//! yet filled, so it has entries with zeroed out data).
+void circular_cache_flush(CircularCache *c);