C.Interface.And.Implementations—table(key-value系统)的实现

1、An  associative table is a set of key-value pairs. It’s like an array except that the indices can be values of any type.


C语言中宏的作用域是文件或者遇到undef为止。


table的实现是以哈希表和链表实现。内存形式如下:

C.Interface.And.Implementations—table(key-value系统)的实现_第1张图片


===========================table.h===============================

#ifndef TABLE_INCLUDED
#define TABLE_INCLUDED

#define T Table_T
typedef struct T *T;

//exported functions
extern T    Table_new(int hint, 
    int cmp(const void *x, const void *y),
    unsigned hash(const void *key));

extern void   Table_free(T *table);

extern int    Table_length(T table);
extern void  *Table_put   (T table, const void *key,
    void *value);
extern void  *Table_get   (T table, const void *key);
extern void  *Table_remove(T table, const void *key);
extern void   Table_map   (T table, 
    void apply(const void *key, void **value, void *cl),
    void *cl);
extern void **Table_toArray(T table, void *end);

#undef T
#endif

=========================table.c===============================

#include <limits.h>
#include <stddef.h>
#include "mem.h"
#include "assert.h"
#include "table.h"

#define T Table_T

//types
struct T{
    //fields
    int size;
    int (*cmp)(const void *x, const void *y);
    unsigned (*hash)(const void *key);
    int length;
    unsigned timestamp;
    struct binding{
        struct binding *link;
        const void *key;
        void *value;
    } **buckets;
};

//static functions
static int cmpatom(const void *x, const void *y){
    return x != y;
}

static unsigned hashatom(const void *key){
    return (unsigned long)key>>2;
}


//functions
T Table_new(int hint,
    int cmp(const void *x, const void *y),
    unsigned hash(const void *key)){
    T table;
    int i;
    static int primes[] = {509, 509, 1021, 2053, 4093,
        8191, 16383, 32771, 65521, INT_MAX };

    assert(hint >= 0);
    for(i = 1; primes[i] < hint; ++i)
        ;
    table = ALLOC(sizeof(*table) + 
        primes[i-1]*sizeof(table->buckets[0]));
    table->size = primes[i-1];
    table->cmp = cmp ? cmp : cmpatom;
    table->hash = hash ? hash : hashatom;
    table->buckets = (struct binding **)(table + 1);
    for(i = 0; i < table->size; ++i)
        table->buckets[i] = NULL;
    table->length = 0;
    table->timestamp = 0;
    
    return table;
}

void *Table_get(T table, const void *key){
    int i;
    struct binding *p;

    assert(table);
    assert(key);
    i = (*table->hash)(key)%table->size;
    for(p = table->buckets[i]; p; p = p->link){
        if((*table->cmp)(key,p->key) == 0 )
            break;
    }

    return p ? p->value : NULL;
}

void *Table_put(T table, const void *key, void *value){
    int i;
    struct binding *p;
    void *prev;

    assert(table);
    assert(key);
    //search table for key
    i = (*table->hash)(key)%table->size;
    for(p = table->buckets[i]; p; p = p->link){
        if((*table->cmp)(key,p->key) == 0)
            break;
    }
    if(p == NULL){
        NEW(p);
        p->key = key;
        p->link = table->buckets[i];
        table->buckets[i] = p;
        table->length++;
        prev = NULL;
    }else{
        prev = p->value;
    }
    p->value = value;
    table->timestamp++;
    return prev;
}

int Table_length(T table){
    assert(table);
    return table->length;
}

void Table_map(T table,
    void apply(const void *key, void **value, void *cl),
    void *cl){
    int i;
    unsigned stamp;
    struct binding *p;

    assert(table);
    assert(apply);
    stamp = table->timestamp;
    for(i = 0; i < table->size; ++i){
        for(p = table->buckets[i]; p; p = p->link){
            apply(p->key, &p->value, cl);
            assert(table->timestamp == stamp);
        }
    }
}

void *Table_remove(T table, const void *key){
    int i;
    struct binding **pp;

    assert(table);
    assert(key);
    table->timestamp++;
    i = (*table->hash)(key)%table->size;
    for(pp = &table->buckets[i]; *pp; pp = &(*pp)->link){
        if((*table->cmp)(key, (*pp)->key) == 0){
            struct binding *p = *pp;
            void *value = p->value;
            *pp = p->link;
            FREE(p);
            table->length--;
            return value;
        }
    }

    return NULL;
}

void **Table_toArray(T table, void *end){
    int i, j = 0;
    void **array;
    struct binding *p;

    assert(table);
    array = ALLOC((2*table->length + 1)*sizeof(*array));
    for(i = 0; i < table->size; ++i){
        for(p = table->buckets[i]; p; p = p->link){
            array[j++] = (void *)p->key;
            array[j++] = p->value;
        }
    }

    array[j] = end;
    return array;
}

void Table_free(T *table){
    assert(table && *table);
    if((*table)->length > 0){
        int i;
        struct binding *p, *q;
        for(i = 0; i < (*table)->size; ++i){
            for(p = (*table)->buckets[i]; p; p = q){
                q = p->link;
                FREE(p);
            }
        }
    }
    FREE(*table);
}


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