linear hash

// linear_hash.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <stdio.h>
#include <assert.h>

#define UNUSED (-1)


/*
 *        Linear Hash is to search a position where is no element used
 *    from the position which hash function specified.
 * Param:
 *    arr: A array to save new element.
 *    len: Length of that array.
 *    x: The new element to put.
 * Rtn:
 *    0: Insert successfully.
 *    -1: No space.
 * Note:
 *    For more details, please see <<Operating Systems Internals 
 * and Design Principles Sixth Edition>> Chinese version page .269
 */
static int linear_hash(int arr[], int len, int x)
{
    assert(NULL != arr) ;
    assert(0 < len) ;

    int cnt = 0 ;                    // Count how many elements has been passed.
    int pos = x % len ;
    while (UNUSED != arr[pos])
    {
        pos = (pos + 1) % len ;

        // When there is no space to restore any
            // new element, function return -1.
        if (++cnt == len - 1)
        {
            return -1 ;
        }
    }

    arr[pos] = x ;
    
    return 0 ;
}


int _tmain(int argc, _TCHAR* argv[])
{
    int arr[] = {UNUSED, 1, 5, UNUSED, UNUSED, 3, UNUSED, 4, UNUSED, 8, UNUSED} ;
    int len = int(sizeof(arr)/sizeof(arr[0])) ;

    for (int i = 0 ; i < (int)sizeof(arr)/sizeof(arr[0]) ;i++)
    {
        printf("%4d ", arr[i]) ;
    }
    puts("") ;

    // '0' should put at arr[0], and arr[0] is unused, 
        // thus arr[0] = 0.
    linear_hash(arr, len, 0) ;
    // '2' should put at arr[2], but arr[2] == 5, 
        // and then,  we look at arr[(2+1) % len], which is UNUSED,
        // thus arr[(2+1) % len] = 2.
    linear_hash(arr, len, 2) ;

    for (int i = 0 ; i < len ;i++)
    {
        printf("%4d ", arr[i]) ;
    }
    puts("") ;

    return 0;
}