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114 lines
3.5 KiB
114 lines
3.5 KiB
2 years ago
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/*********************************************************************
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* Copyright 2018, UCAR/Unidata
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* See netcdf/COPYRIGHT file for copying and redistribution conditions.
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* $Header$
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*********************************************************************/
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#ifndef NCHASHMAP_H
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#define NCHASHMAP_H
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#if HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <stdint.h>
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/*
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This hashmap is optimized to assume null-terminated strings as the
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key.
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Data is presumed to be an index into some other table Assume it
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can be compared using simple == The key is some hash of some
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null terminated string.
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One problem here is that we need to do a final equality check on
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the name string to avoid an accidental hash collision. It would
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be nice if we had a large enough hashkey that was known to have
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an extremely low probability of collisions so we could compare
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the hashkeys to determine exact match. A quick internet search
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indicates that this is rather more tricky than just using
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e.g. crc64 or such. Needs some thought.
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*/
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/*! Hashmap-related structs.
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NOTES:
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1. 'data' is the an arbitrary uintptr_t integer or void* pointer.
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2. hashkey is a crc32 hash of key
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WARNINGS:
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1. It is critical that |uintptr_t| == |void*|
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*/
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/** The type and # bits in a hashkey */
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#ifndef nchashkey_t
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#define nchashkey_t unsigned
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#define NCHASHKEYBITS (sizeof(nchashkey_t)*8)
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#endif
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typedef struct NC_hentry {
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int flags;
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uintptr_t data;
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nchashkey_t hashkey; /* Hash id (crc)*/
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size_t keysize;
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char* key; /* copy of the key string; kept as unsigned char */
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} NC_hentry;
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/*
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The hashmap object must give us the hash table (table),
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the |table| size, and the # of defined entries in the table
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*/
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typedef struct NC_hashmap {
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size_t alloc; /* allocated # of entries */
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size_t active; /* # of active entries */
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NC_hentry* table;
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} NC_hashmap;
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/* defined in nchashmap.c */
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/*
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There are two "kinds" of functions:
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1. those that take the key+size -- they compute the hashkey internally.
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2. those that take the hashkey directly
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*/
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/** Creates a new hashmap near the given size. */
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extern NC_hashmap* NC_hashmapnew(size_t startsize);
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/** Inserts a new element into the hashmap; takes key+size */
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/* key points to size bytes to convert to hash key */
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extern int NC_hashmapadd(NC_hashmap*, uintptr_t data, const char* key, size_t keysize);
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/** Removes the storage for the element of the key; takes key+size.
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Return 1 if found, 0 otherwise; returns the data in datap if !null
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*/
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extern int NC_hashmapremove(NC_hashmap*, const char* key, size_t keysize, uintptr_t* datap);
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/** Returns the data for the key; takes key+size.
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Return 1 if found, 0 otherwise; returns the data in datap if !null
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*/
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extern int NC_hashmapget(NC_hashmap*, const char* key, size_t keysize, uintptr_t* datap);
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/** Change the data for the specified key; takes hashkey.
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Return 1 if found, 0 otherwise
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*/
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extern int NC_hashmapsetdata(NC_hashmap*, const char* key, size_t keylen, uintptr_t newdata);
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/** Returns the number of active elements. */
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extern size_t NC_hashmapcount(NC_hashmap*);
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/** Reclaims the hashmap structure. */
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extern int NC_hashmapfree(NC_hashmap*);
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/* Return the hash key for specified key; takes key+size*/
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extern nchashkey_t NC_hashmapkey(const char* key, size_t size);
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/* Return the ith entry info:
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@param map
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@param i
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@param entryp contains 0 if not active, otherwise the data
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@param keyp contains null if not active, otherwise the key
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@return NC_EINVAL if no more entries
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*/
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extern int NC_hashmapith(NC_hashmap* map, size_t i, uintptr_t* datap, const char** keyp);
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#endif /*NCHASHMAP_H*/
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