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62 lines
2.2 KiB
C
62 lines
2.2 KiB
C
#pragma once
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#include <stddef.h>
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/// Type for hash number (hash calculation result).
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typedef size_t hash_T;
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/// Hashtable item.
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///
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/// Each item has a NUL terminated string key.
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/// A key can appear only once in the table.
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///
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/// A hash number is computed from the key for quick lookup. When the hashes
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/// of two different keys point to the same entry an algorithm is used to
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/// iterate over other entries in the table until the right one is found.
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/// To make the iteration work removed keys are different from entries where a
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/// key was never present.
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///
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/// Note that this does not contain a pointer to the key and another pointer to
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/// the value. Instead, it is assumed that the key is contained within the
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/// value, so that you can get a pointer to the value subtracting an offset from
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/// the pointer to the key.
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/// This reduces the size of this item by 1/3.
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typedef struct {
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/// Cached hash number for hi_key.
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hash_T hi_hash;
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/// Item key.
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///
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/// Possible values mean the following:
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/// NULL : Item was never used.
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/// HI_KEY_REMOVED : Item was removed.
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/// (Any other pointer value) : Item is currently being used.
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char *hi_key;
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} hashitem_T;
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enum {
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/// Initial size for a hashtable.
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/// Our items are relatively small and growing is expensive, thus start with 16.
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/// Must be a power of 2.
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/// This allows for storing 10 items (2/3 of 16) before a resize is needed.
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HT_INIT_SIZE = 16,
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};
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/// An array-based hashtable.
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///
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/// Keys are NUL terminated strings. They cannot be repeated within a table.
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/// Values are of any type.
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///
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/// The hashtable grows to accommodate more entries when needed.
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typedef struct {
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hash_T ht_mask; ///< mask used for hash value
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///< (nr of items in array is "ht_mask" + 1)
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size_t ht_used; ///< number of items used
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size_t ht_filled; ///< number of items used or removed
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int ht_changed; ///< incremented when adding or removing an item
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int ht_locked; ///< counter for hash_lock()
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hashitem_T *ht_array; ///< points to the array, allocated when it's
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///< not "ht_smallarray"
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hashitem_T ht_smallarray[HT_INIT_SIZE]; ///< initial array
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} hashtab_T;
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