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111 lines
2.8 KiB
C
111 lines
2.8 KiB
C
/*
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* Copyright 2024 Google LLC
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "lru_cache.h"
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#include "system/passert.h"
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#include <string.h>
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void lru_cache_init(LRUCache* c, size_t item_size, uint8_t *buffer, size_t buffer_size) {
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*c = (LRUCache) {
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.buffer = buffer,
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.item_size = item_size,
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.max_items = buffer_size / (item_size + sizeof(CacheEntry)),
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.least_recent = NULL
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};
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}
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static CacheEntry *entry_for_index(LRUCache *c, int index) {
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return ((CacheEntry *)(c->buffer + index * (sizeof(CacheEntry) + c->item_size)));
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}
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void lru_cache_flush(LRUCache *c) {
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c->least_recent = NULL;
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}
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void *lru_cache_get(LRUCache* c, uint32_t key) {
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// cur_ptr is a pointer-to-pointer to the more_recent
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// field in the parent of the current entry
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CacheEntry **cur_ptr = &c->least_recent;
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CacheEntry *found = NULL;
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for (int i = 0; i < c->max_items; ++i) {
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CacheEntry *cur_entry = *cur_ptr;
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if (cur_entry == NULL) {
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break;
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}
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if (cur_entry->key == key) {
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*cur_ptr = cur_entry->more_recent;
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found = cur_entry;
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}
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if (*cur_ptr == NULL) {
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break;
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}
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cur_ptr = &cur_entry->more_recent;
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}
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// cur_ptr should point to the last pointer in the list
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PBL_ASSERTN(*cur_ptr == NULL);
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if (found) {
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found->more_recent = NULL;
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*cur_ptr = found;
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return (found->data);
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} else {
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return (NULL);
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}
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}
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void lru_cache_put(LRUCache* c, uint32_t key, void* item) {
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// cur_ptr is a pointer-to-pointer to the more_recent
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// field in the parent of the current entry
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CacheEntry **cur_ptr = &c->least_recent;
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CacheEntry *new = NULL;
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for (int i = 0; i < c->max_items; ++i) {
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CacheEntry *cur_entry = *cur_ptr;
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if (cur_entry == NULL) {
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// cache is not full
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new = entry_for_index(c, i);
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break;
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} else if (cur_entry->key == key) {
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// key already in cache, update
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*cur_ptr = cur_entry->more_recent;
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new = cur_entry;
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}
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if (*cur_ptr == NULL) {
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break;
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}
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cur_ptr = &cur_entry->more_recent;
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}
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// cur_ptr should point to the last pointer in the list
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PBL_ASSERTN(*cur_ptr == NULL);
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if (new == NULL) {
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// cache full, evict LRU
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new = c->least_recent;
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c->least_recent = new->more_recent;
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}
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new->more_recent = NULL;
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new->key = key;
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memcpy(new->data, item, c->item_size);
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*cur_ptr = new;
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}
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