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+/**
+ * @file hash_table_internal.h
+ * @author Radek Krejci <rkrejci@cesnet.cz>
+ * @author Michal Vasko <mvasko@cesnet.cz>
+ * @brief libyang hash table internal header
+ *
+ * Copyright (c) 2015 - 2023 CESNET, z.s.p.o.
+ *
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://opensource.org/licenses/BSD-3-Clause
+ */
+
+#ifndef LY_HASH_TABLE_INTERNAL_H_
+#define LY_HASH_TABLE_INTERNAL_H_
+
+#include <pthread.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include "compat.h"
+#include "hash_table.h"
+
+/** reference value for 100% */
+#define LYHT_HUNDRED_PERCENTAGE 100
+
+/** when the table is at least this much percent full, it is enlarged (double the size) */
+#define LYHT_ENLARGE_PERCENTAGE 75
+
+/** only once the table is this much percent full, enable shrinking */
+#define LYHT_FIRST_SHRINK_PERCENTAGE 50
+
+/** when the table is less than this much percent full, it is shrunk (half the size) */
+#define LYHT_SHRINK_PERCENTAGE 25
+
+/** never shrink beyond this size */
+#define LYHT_MIN_SIZE 8
+
+/**
+ * @brief Generic hash table record.
+ */
+struct ly_ht_rec {
+    uint32_t hash;        /* hash of the value */
+    uint32_t next;        /* index of next collision */
+    unsigned char val[1]; /* arbitrary-size value */
+} _PACKED;
+
+/* real size, without taking the val[1] in account */
+#define SIZEOF_LY_HT_REC (sizeof(struct ly_ht_rec) - 1)
+
+struct ly_ht_hlist {
+    uint32_t first;
+    uint32_t last;
+};
+
+/**
+ * @brief (Very) generic hash table.
+ *
+ * This structure implements a hash table, providing fast accesses to stored
+ * values from their hash.
+ *
+ * The hash table structure contains 2 pointers to tables that are allocated
+ * at initialization:
+ * - a table of records: each record is composed of a struct ly_ht_rec header,
+ *   followed by the user value. The header contains the hash value and a
+ *   next index that can be used to chain records.
+ * - a table of list heads: each list head entry contains the index of the
+ *   first record in the records table whose hash (modulo hash table size)
+ *   is equal to the index of the list head entry. The other matching records
+ *   are chained together.
+ *
+ * The unused records are chained in first_free_rec, which contains the index
+ * of the first unused record entry in the records table.
+ *
+ * The LYHT_NO_RECORD magic value is used when an index points to nothing.
+ */
+struct ly_ht {
+    uint32_t used;        /* number of values stored in the hash table (filled records) */
+    uint32_t size;        /* always holds 2^x == size (is power of 2), actually number of records allocated */
+    lyht_value_equal_cb val_equal; /* callback for testing value equivalence */
+    void *cb_data;        /* user data callback arbitrary value */
+    uint16_t resize;      /* 0 - resizing is disabled, *
+                           * 1 - enlarging is enabled, *
+                           * 2 - both shrinking and enlarging is enabled */
+    uint16_t rec_size;    /* real size (in bytes) of one record for accessing recs array */
+    uint32_t first_free_rec; /* index of the first free record */
+    struct ly_ht_hlist *hlists; /* pointer to the hlists table */
+    unsigned char *recs;  /* pointer to the hash table itself (array of struct ht_rec) */
+};
+
+/* index that points to nothing */
+#define LYHT_NO_RECORD UINT32_MAX
+
+/* get the record associated to */
+static inline struct ly_ht_rec *
+lyht_get_rec(unsigned char *recs, uint16_t rec_size, uint32_t idx)
+{
+    return (struct ly_ht_rec *)&recs[idx * rec_size];
+}
+
+/* Iterate all records in a hlist */
+#define LYHT_ITER_HLIST_RECS(ht, hlist_idx, rec_idx, rec)               \
+    for (rec_idx = ht->hlists[hlist_idx].first,                         \
+             rec = lyht_get_rec(ht->recs, ht->rec_size, rec_idx);       \
+         rec_idx != LYHT_NO_RECORD;                                     \
+         rec_idx = rec->next,                                           \
+             rec = lyht_get_rec(ht->recs, ht->rec_size, rec_idx))
+
+/* Iterate all records in the hash table */
+#define LYHT_ITER_ALL_RECS(ht, hlist_idx, rec_idx, rec)              \
+    for (hlist_idx = 0; hlist_idx < ht->size; hlist_idx++)           \
+        LYHT_ITER_HLIST_RECS(ht, hlist_idx, rec_idx, rec)
+
+/**
+ * @brief Dictionary hash table record.
+ */
+struct ly_dict_rec {
+    char *value;        /**< stored string */
+    uint32_t refcount;  /**< reference count of the string */
+};
+
+/**
+ * @brief Dictionary for storing repeated strings.
+ */
+struct ly_dict {
+    struct ly_ht *hash_tab;
+    pthread_mutex_t lock;
+};
+
+/**
+ * @brief Initiate content (non-zero values) of the dictionary
+ *
+ * @param[in] dict Dictionary table to initiate
+ */
+void lydict_init(struct ly_dict *dict);
+
+/**
+ * @brief Cleanup the dictionary content
+ *
+ * @param[in] dict Dictionary table to cleanup
+ */
+void lydict_clean(struct ly_dict *dict);
+
+#endif /* LY_HASH_TABLE_INTERNAL_H_ */