hash.c

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//--------------------------------------------------------------------------
//
// File:           hash.c
//
// Purpose:        Hash table implementation
//
// Author:         Jerry Coffin
//
// Description:    Public domain code by Jerry Coffin, with improvements by
//                 HenkJan Wolthuis.
//                 Date last modified: 05-Jul-1997
//
// Revisions:      18-09-2002 -- modified by Pavel Sakov
//
//--------------------------------------------------------------------------

#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include "hash.h"

#define INT_PER_DOUBLE    2

//* A hash table consists of an array of these buckets.
//
typedef struct ht_bucket
{
    void * key;
    void            * data;
    int  id;                    // unique id -- just in case
    struct ht_bucket* next;
} ht_bucket;

//* Hash table structure.
// Note that more nodes than `size' can be inserted in the table,
// but performance degrades as this happens.
//
struct hashtable
{
    int         size;           // table size
    int         n;              // current number of entries
    int         naccum;         // number of inserted entries
    int         nhash;          // number of used table elements
    ht_keycp    cp;
    ht_keyeq    eq;
    ht_key2hash hash;
    ht_bucket   ** table;
};

int d1eq( void* key1, void* key2 );

// Creates a hashtable of specified size.
//
hashtable* ht_create( int size, ht_keycp cp, ht_keyeq eq, ht_key2hash hash )
{
    hashtable* table = malloc( sizeof ( hashtable ) );
    ht_bucket** bucket;
    int      i;

    assert( sizeof ( double ) == INT_PER_DOUBLE * sizeof ( int ) );
    //
    // (used in d1hash() and d2hash())
    //

    if ( table == NULL )
        return NULL;

    if ( size <= 0 )
    {
        free( table );
        return NULL;
    }

    table->size  = size;
    table->table = malloc( sizeof ( ht_bucket* ) * (size_t) size );
    bucket       = table->table;

    if ( bucket == NULL )
    {
        free( table );
        return NULL;
    }

    for ( i = 0; i < size; ++i )
        bucket[i] = NULL;
    table->n      = 0;
    table->naccum = 0;
    table->nhash  = 0;
    table->eq     = eq;
    table->cp     = cp;
    table->hash   = hash;

    return table;
}

// Destroys a hash table.
// (Take care of deallocating data by ht_process() prior to destroying the
// table if necessary.)
//
// @param table Hash table to be destroyed
//
void ht_destroy( hashtable* table )
{
    int i;

    if ( table == NULL )
        return;

    for ( i = 0; i < table->size; ++i )
    {
        ht_bucket* bucket;

        for ( bucket = ( table->table )[i]; bucket != NULL; )
        {
            ht_bucket* prev = bucket;

            free( bucket->key );
            bucket = bucket->next;
            free( prev );
        }
    }

    free( table->table );
    free( table );
}

// Inserts a new entry into the hash table.
//
// @param table The hash table
// @param key Ponter to entry's key
// @param data Pointer to associated data
// @return Pointer to the old data associated with the key, NULL if the key
//         wasn't in the table previously
//
void* ht_insert( hashtable* table, void* key, void* data )
{
    unsigned int val = table->hash( key ) % (unsigned int) table->size;
    ht_bucket    * bucket;

    //
    // NULL means this bucket hasn't been used yet.  We'll simply allocate
    // space for our new bucket and put our data there, with the table
    // pointing at it.
    //
    if ( ( table->table )[val] == NULL )
    {
        bucket = malloc( sizeof ( ht_bucket ) );
        if ( bucket == NULL )
            return NULL;

        bucket->key  = table->cp( key );
        bucket->next = NULL;
        bucket->data = data;
        bucket->id   = table->naccum;

        ( table->table )[val] = bucket;
        table->n++;
        table->naccum++;
        table->nhash++;

        return bucket->data;
    }

    //
    // This spot in the table is already in use.  See if the current string
    // has already been inserted, and if so, return corresponding data.
    //
    for ( bucket = ( table->table )[val]; bucket != NULL; bucket = bucket->next )
        if ( table->eq( key, bucket->key ) == 1 )
        {
            void* old_data = bucket->data;

            bucket->data = data;
            bucket->id   = table->naccum;
            table->naccum++;

            return old_data;
        }

    //
    // This key must not be in the table yet.  We'll add it to the head of
    // the list at this spot in the hash table.  Speed would be slightly
    // improved if the list was kept sorted instead.  In this case, this
    // code would be moved into the loop above, and the insertion would take
    // place as soon as it was determined that the present key in the list
    // was larger than this one.
    //
    bucket = (ht_bucket *) malloc( sizeof ( ht_bucket ) );
    if ( bucket == NULL )
        return 0;
    bucket->key  = table->cp( key );
    bucket->data = data;
    bucket->next = ( table->table )[val];
    bucket->id   = table->naccum;

    ( table->table )[val] = bucket;
    table->n++;
    table->naccum++;

    return data;
}

// Returns a pointer to the data associated with a key.  If the key has
// not been inserted in the table, returns NULL.
//
// @param table The hash table
// @param key The key
// @return The associated data or NULL
//
void* ht_find( hashtable* table, void* key )
{
    unsigned int val = table->hash( key ) % (unsigned int) table->size;
    ht_bucket    * bucket;

    if ( ( table->table )[val] == NULL )
        return NULL;

    for ( bucket = ( table->table )[val]; bucket != NULL; bucket = bucket->next )
        if ( table->eq( key, bucket->key ) == 1 )
            return bucket->data;

    return NULL;
}

// Deletes an entry from the table.  Returns a pointer to the data that
// was associated with the key so that the calling code can dispose it
// properly.
//
// @param table The hash table
// @param key The key
// @return The associated data or NULL
//
void* ht_delete( hashtable* table, void* key )
{
    unsigned int val = table->hash( key ) % (unsigned int) table->size;
    ht_bucket    * prev;
    ht_bucket    * bucket;
    void         * data;

    if ( ( table->table )[val] == NULL )
        return NULL;

    //
    // Traverse the list, keeping track of the previous node in the list.
    // When we find the node to delete, we set the previous node's next
    // pointer to point to the node after ourself instead.  We then delete
    // the key from the present node, and return a pointer to the data it
    // contains.
    //
    for ( prev = NULL, bucket = ( table->table )[val]; bucket != NULL; prev = bucket, bucket = bucket->next )
    {
        if ( table->eq( key, bucket->key ) == 1 )
        {
            data = bucket->data;
            if ( prev != NULL )
                prev->next = bucket->next;
            else
            {
                //
                // If 'prev' still equals NULL, it means that we need to
                // delete the first node in the list. This simply consists
                // of putting our own 'next' pointer in the array holding
                // the head of the list.  We then dispose of the current
                // node as above.
                //
                ( table->table )[val] = bucket->next;
                table->nhash--;
            }
            free( bucket->key );
            free( bucket );
            table->n--;

            return data;
        }
    }

    //
    // If we get here, it means we didn't find the item in the table. Signal
    // this by returning NULL.
    //
    return NULL;
}

// For each entry, calls a specified function with corresponding data as a
// parameter.
//
// @param table The hash table
// @param func The action function
//
void ht_process( hashtable* table, void ( *func )( void* ) )
{
    int i;

    for ( i = 0; i < table->size; ++i )
        if ( ( table->table )[i] != NULL )
        {
            ht_bucket* bucket;

            for ( bucket = ( table->table )[i]; bucket != NULL; bucket = bucket->next )
                func( bucket->data );
        }
}

//
// functions for for string keys
//

static unsigned int strhash( void* key )
{
    char         * str     = (char *) key;
    unsigned int hashvalue = 0;

    while ( *str != 0 )
    {
        hashvalue  ^= *(unsigned int *) str;
        hashvalue <<= 1;
        str++;
    }

    return hashvalue;
}

static void* strcp( void* key )
{
    return (void *) strdup( (const char *) key );
}

static int streq( void* key1, void* key2 )
{
    return !strcmp( key1, key2 );
}

// functions for for double keys

static unsigned int d1hash( void* key )
{
    unsigned int* v = (unsigned int *) key;

#if INT_PER_DOUBLE == 2
    return v[0] + v[1];
#else
#error not implemented
#endif
}

static void* d1cp( void* key )
{
    double* newkey = malloc( sizeof ( double ) );

    *newkey = *(double *) key;

    return newkey;
}

int d1eq( void* key1, void* key2 )
{
    return *(double *) key1 == *(double *) key2;
}

//
// functions for for double[2] keys
//

#include "math.h"

static unsigned int d2hash( void* key )
{
    unsigned int* v = (unsigned int *) key;

#if INT_PER_DOUBLE == 2
    //
    // PS: here multiplications suppose to make (a,b) and (b,a) generate
    // different hash values
    //
    return v[0] + v[1] + v[2] * 3 + v[3] * 7;
#else
#error not implemented
#endif
}

static void* d2cp( void* key )
{
    double* newkey = malloc( sizeof ( double ) * 2 );

    newkey[0] = ( (double *) key )[0];
    newkey[1] = ( (double *) key )[1];

    return newkey;
}

static int d2eq( void* key1, void* key2 )
{
    return ( ( (double *) key1 )[0] == ( (double *) key2 )[0] ) && ( ( (double *) key1 )[1] == ( (double *) key2 )[1] );
}

hashtable* ht_create_d1( int size )
{
    return ht_create( size, d1cp, d1eq, d1hash );
}

hashtable* ht_create_d2( int size )
{
    return ht_create( size, d2cp, d2eq, d2hash );
}

hashtable* ht_create_str( int size )
{
    return ht_create( size, strcp, streq, strhash );
}

#ifdef HT_TEST

#include <stdio.h>
#include <limits.h>

#define BUFSIZE    1024

static void print_double( void* data )
{
    printf( " \"%d\"", (int) *(double *) data );
}

static void print_string( void* data )
{
    printf( " \"%s\"", (char *) data );
}

int main()
{
    double   points[] = {
        922803.7855, 7372394.688,   0,
        922849.2037, 7372307.027,   1,
        922894.657,  7372219.306,   2,
        922940.1475, 7372131.528,   3,
        922985.6777, 7372043.692,   4,
        923031.2501, 7371955.802,   5,
        923076.8669, 7371867.857,   6,
        923122.5307, 7371779.861,   7,
        923168.2439, 7371691.816,   8,
        923214.0091, 7371603.722,   9,
        923259.8288, 7371515.583,  10,
        922891.3958, 7372440.117,  11,
        922936.873,  7372352.489,  12,
        922982.3839, 7372264.804,  13,
        923027.9308, 7372177.064,  14,
        923073.5159, 7372089.268,  15,
        923119.1415,  7372001.42,  16,
        923164.8099, 7371913.521,  17,
        923210.5233, 7371825.572,  18,
        923256.2841, 7371737.575,  19,
        923302.0946, 7371649.534,  20,
        923347.9572,  7371561.45,  21,
        922978.9747, 7372485.605,  22,
        923024.5085, 7372398.009,  23,
        923070.0748, 7372310.358,  24,
        923115.6759, 7372222.654,  25,
        923161.3136, 7372134.897,  26,
        923206.9903,  7372047.09,  27,
        923252.7079, 7371959.233,  28,
        923298.4686,  7371871.33,  29,
        923344.2745, 7371783.381,  30,
        923390.1279, 7371695.389,  31,
        923436.0309, 7371607.357,  32,
        923066.5232, 7372531.148,  33,
        923112.1115, 7372443.583,  34,
        923157.7311, 7372355.966,  35,
        923203.3842, 7372268.296,  36,
        923249.0725, 7372180.577,  37,
        923294.7981, 7372092.808,  38,
        923340.5628, 7372004.993,  39,
        923386.3686, 7371917.132,  40,
        923432.2176, 7371829.229,  41,
        923478.1116, 7371741.284,  42,
        923524.0527, 7371653.302,  43,
        923154.0423, 7372576.746,  44,
        923199.6831, 7372489.211,  45,
        923245.3541, 7372401.625,  46,
        923291.0572, 7372313.989,  47,
        923336.7941, 7372226.305,  48,
        923382.5667, 7372138.574,  49,
        923428.3766, 7372050.798,  50,
        923474.2256, 7371962.978,  51,
        923520.1155, 7371875.118,  52,
        923566.0481, 7371787.218,  53,
        923612.0252, 7371699.282,  54,
        923241.533,  7372622.396,  55,
        923287.2244, 7372534.889,  56,
        923332.9449, 7372447.334,  57,
        923378.6963, 7372359.731,  58,
        923424.4801, 7372272.081,  59,
        923470.2979, 7372184.385,  60,
        923516.1513, 7372096.646,  61,
        923562.0418, 7372008.866,  62,
        923607.9709, 7371921.046,  63,
        923653.9402, 7371833.188,  64,
        923699.9514, 7371745.296,  65,
        923328.9962, 7372668.095,  66,
        923374.7365, 7372580.617,  67,
        923420.5049, 7372493.091,  68,
        923466.303,  7372405.519,  69,
        923512.1321, 7372317.901,  70,
        923557.9936,  7372230.24,  71,
        923603.8889, 7372142.536,  72,
        923649.8192, 7372054.793,  73,
        923695.786,  7371967.011,  74,
        923741.7905, 7371879.193,  75,
        923787.8341, 7371791.342,  76,
        923416.4327, 7372713.844,  77,
        923462.2204, 7372626.393,  78,
        923508.0353, 7372538.895,  79,
        923553.8787, 7372451.353,  80,
        923599.7517, 7372363.766,  81,
        923645.6555, 7372276.137,  82,
        923691.5914, 7372188.467,  83,
        923737.5603, 7372100.757,  84,
        923783.5634, 7372013.011,  85,
        923829.6017, 7371925.231,  86,
        923875.6763, 7371837.419,  87,
        923503.8433,  7372759.64,  88,
        923549.6771, 7372672.214,  89,
        923595.5372, 7372584.744,  90,
        923641.4246,  7372497.23,  91,
        923687.3404, 7372409.673,  92,
        923733.2855, 7372322.074,  93,
        923779.2608, 7372234.436,  94,
        923825.2672, 7372146.759,  95,
        923871.3056, 7372059.047,  96,
        923917.3766, 7371971.301,  97,
        923963.4812, 7371883.524,  98,
        923591.2288, 7372805.481,  99,
        923637.1076, 7372718.081, 100,
        923683.0118, 7372630.638, 101,
        923728.9423, 7372543.151, 102,
        923774.8998, 7372455.622, 103,
        923820.8852, 7372368.052, 104,
        923866.8991, 7372280.443, 105,
        923912.9422, 7372192.797, 106,
        923959.015,  7372105.116, 107,
        924005.118,  7372017.402, 108,
        924051.2518, 7371929.657, 109,
        923678.5898, 7372851.367, 110,
        923724.5126, 7372763.992, 111,
        923770.46,   7372676.574, 112,
        923816.4328, 7372589.113, 113,
        923862.4314, 7372501.611, 114,
        923908.4564, 7372414.069, 115,
        923954.5083, 7372326.488, 116,
        924000.5875,  7372238.87, 117,
        924046.6941, 7372151.218, 118,
        924092.8286, 7372063.533, 119,
        924138.9911, 7371975.818, 120
    };

    int      size = sizeof ( points ) / sizeof ( double ) / 3;
    hashtable* ht;
    int      i;

    //
    // double[2] key
    //

    printf( "\n1. Testing a table with key of double[2] type\n\n" );

    printf( "  creating a table..." );
    ht = ht_create_d2( size );
    printf( "done\n" );

    printf( "  inserting %d values from a file...", size );
    for ( i = 0; i < size; ++i )
        ht_insert( ht, &points[i * 3], &points[i * 3 + 2] );
    printf( "done\n" );

    printf( "  stats:\n" );
    printf( "    %d entries, %d table elements, %d filled elements\n", ht->n, ht->size, ht->nhash );
    printf( "    %f entries per hash value in use\n", (double) ht->n / ht->nhash );

    printf( "  finding and printing each 10th data:\n" );
    for ( i = 0; i < size; i += 10 )
    {
        double* point = &points[i * 3];
        double* data  = ht_find( ht, point );

        if ( data != NULL )
            printf( "    i = %d; data = \"%d\"\n", i, (int) *data );
        else
            printf( "    i = %d; data = <none>\n", i );
    }

    printf( "  removing every 3rd element..." );
    for ( i = 0; i < size; i += 3 )
    {
        double* point = &points[i * 3];
        ht_delete( ht, point );
    }
    printf( "done\n" );

    printf( "  stats:\n" );
    printf( "    %d entries, %d table elements, %d filled elements\n", ht->n, ht->size, ht->nhash );
    printf( "    %f entries per hash value in use\n", (double) ht->n / ht->nhash );

    printf( "  finding and printing each 10th data:\n" );
    for ( i = 0; i < size; i += 10 )
    {
        double* point = &points[i * 3];
        double* data  = ht_find( ht, point );

        if ( data != NULL )
            printf( "    i = %d; data = \"%d\"\n", i, (int) *data );
        else
            printf( "    i = %d; data = <none>\n", i );
    }

    printf( "  printing all data by calling ht_process():\n " );
    ht_process( ht, print_double );

    printf( "\n  destroying the hash table..." );
    ht_destroy( ht );
    printf( "done\n" );

    //
    // char* key
    //

    printf( "\n2. Testing a table with key of char* type\n\n" );

    printf( "  creating a table..." );
    ht = ht_create_str( size );
    printf( "done\n" );

    printf( "  inserting %d elements with deep copy of each data string...", size );
    for ( i = 0; i < size; ++i )
    {
        char key[BUFSIZE];
        char str[BUFSIZE];
        char * data;

        sprintf( key, "%d-th key", i );
        sprintf( str, "%d-th data", i );
        data = strdup( str );
        ht_insert( ht, key, data );
    }
    printf( "done\n" );

    printf( "  stats:\n" );
    printf( "    %d entries, %d table elements, %d filled elements\n", ht->n, ht->size, ht->nhash );
    printf( "    %f entries per hash value in use\n", (double) ht->n / ht->nhash );

    printf( "  finding and printing each 10th data:\n" );
    for ( i = 0; i < size; i += 10 )
    {
        char key[BUFSIZE];
        char * data;

        sprintf( key, "%d-th key", i );
        data = ht_find( ht, key );
        if ( data != NULL )
            printf( "    i = %d; data = \"%s\"\n", i, data );
        else
            printf( "    i = %d; data = <none>\n", i );
    }

    printf( "  removing every 3rd element..." );
    for ( i = 0; i < size; i += 3 )
    {
        char key[BUFSIZE];

        sprintf( key, "%d-th key", i );
        free( ht_delete( ht, key ) );
    }
    printf( "done\n" );

    printf( "  stats:\n" );
    printf( "    %d entries, %d table elements, %d filled elements\n", ht->n, ht->size, ht->nhash );
    printf( "    %f entries per hash value in use\n", (double) ht->n / ht->nhash );

    printf( "  finding and printing each 10th data:\n" );
    for ( i = 0; i < size; i += 10 )
    {
        char key[BUFSIZE];
        char * data;

        sprintf( key, "%d-th key", i );
        data = ht_find( ht, key );
        if ( data != NULL )
            printf( "    i = %d; data = \"%s\"\n", i, data );
        else
            printf( "    i = %d; data = <none>\n", i );
    }

    printf( "  printing all data by calling ht_process():\n " );
    ht_process( ht, print_string );

    printf( "\n  freeing the remaining data by calling ht_process()..." );
    ht_process( ht, free );
    printf( "done\n" );

    printf( "  destroying the hash table..." );
    ht_destroy( ht );
    printf( "done\n" );

    return 0;
}

#endif                          // HT_TEST