windows-nt/Source/XPSP1/NT/shell/ext/url/hash.c

//
// Copyright (c) Microsoft Corporation 1991-1993
//
// File: Hash.c
//
// Comments:
//      This file contains functions that are roughly equivelent to the
//      kernel atom function.  There are two main differences.  The first
//      is that in 32 bit land the tables are maintined in our shared heap,
//      which makes it shared between all of our apps.  The second is that
//      we can assocate a long pointer with each of the items, which in many
//      cases allows us to keep from having to do a secondary lookup from
//      a different table
//
// History:
//  09/08/93 - Created  KurtE
//
//---------------------------------------------------------------------------

#ifdef STRICT
#undef STRICT
#endif
#define NO_SHELL_HEAP_ALLOCATOR  //Kludge to get around new mem heaps in nt

#define NO_SHELL_VALIDATION

// to fix assert problem
#ifdef ASSERT
#undef ASSERT
#endif

#include "project.h"
#include "urlshell.h"
#include <platform.h>


//--------------------------------------------------------------------------
// First define a data structure to use to maintain the list

#define PRIME   37

// NOTE a PHASHITEM is defined as a LPCSTR externaly (for old code to work)
#undef PHASHITEM
typedef struct _HashItem FAR * PHASHITEM;

typedef struct _HashItem
{
    PHASHITEM   phiNext;        //
    UINT        wCount;         // Usage count
    BYTE        cbLen;          // Length of name in characters.
    char        szName[1];      // name
} HASHITEM;

typedef struct _HashTable
{
    UINT    wBuckets;           // Number of buckets
    UINT    wcbExtra;           // Extra bytes per item
    BOOL    fUpperCase;         // Uppercase names
    PHASHITEM phiLast;          // Pointer to the last item we worked with
    PHASHITEM ahiBuckets[EMPTY_SIZE];    // Set of buckets for the table
} HASHTABLE, FAR * PHASHTABLE;

#define HIFROMSZ(sz)  ((PHASHITEM)((BYTE*)(sz) - FIELDOFFSET(HASHITEM, szName)))
#define HIDATAPTR(sz) ((DWORD UNALIGNED *)((BYTE*)(sz) + HIFROMSZ(sz)->cbLen+1))

#define  LOOKUPHASHITEM     0
#define  ADDHASHITEM        1
#define  DELETEHASHITEM     2

static PHASHTABLE g_pHashTable = NULL;

PHASHTABLE NEAR PASCAL GetGlobalHashTable();

//--------------------------------------------------------------------------
// This function looks up the name in the hash table and optionally does
// things like add it, or delete it.
//

//// FEATURE
// we will need to serialize this eventually.

LPCSTR NEAR PASCAL LookupItemInHashTable(PHASHTABLE pht, LPCSTR pszName, int iOp)
{
    // First thing to do is calculate the hash value for the item
    DWORD   dwHash = 0;
    UINT    wBucket;
    BYTE    cbName = 0;
    BYTE    c;
    PHASHITEM phi, phiPrev;
    LPCSTR psz = pszName;

    if (pht == NULL) {
        pht = GetGlobalHashTable();
    }

    if (pht)
    {
        while (*psz)
        {
            // Same type of hash like HashItem manager
            c = *psz++;

            if (pht->fUpperCase && ( c >= 'a') && (c <= 'z'))
                c = c - 'a' + 'A';
            dwHash += (c << 1) + (c >> 1) + c;
            cbName++;
            ASSERT(cbName);

            if (cbName == 0)
                return(NULL);       // Length to long!
        }

        // now search for the item in the buckets.
        phiPrev = NULL;
        ENTERCRITICAL;
        phi = pht->ahiBuckets[wBucket = (UINT)(dwHash % pht->wBuckets)];

        while (phi)
        {
            if (phi->cbLen == cbName)
            {
                if (pht->fUpperCase)
                {
                    if (!lstrcmpi(pszName, phi->szName))
                        break;      // Found match
                }
                else
                {
                    if (!lstrcmp(pszName, phi->szName))
                        break;      // Found match
                }
            }
            phiPrev = phi;      // Keep the previous item
            phi = phi->phiNext;
        }

        //
        // Sortof gross, but do the work here
        //
        switch (iOp)
        {
        case ADDHASHITEM:
            if (phi)
            {
                // Simply increment the reference count
    #ifdef HITTRACE
                DebugMsg(DM_TRACE, "Add Hit on '%s'", pszName);
    #endif
                phi->wCount++;
            }
            else
            {
    #ifdef HITTRACE
                DebugMsg(DM_TRACE, "Add MISS on '%s'", pszName);
    #endif
                // Not Found, try to allocate it out of the heap
                phi = (PHASHITEM)Alloc(sizeof(HASHITEM) + cbName + pht->wcbExtra);

                if (phi != NULL)
                {
                    // Initialize it
                    phi->wCount = 1;        // One use of it
                    phi->cbLen = cbName;        // The length of it;
                    lstrcpy(phi->szName, pszName);

                    // And link it in to the right bucket
                    phi->phiNext = pht->ahiBuckets[wBucket];
                    pht->ahiBuckets[wBucket] = phi;
                }
            }
            pht->phiLast = phi;
            break;

        case DELETEHASHITEM:
            if (phi)
            {
                phi->wCount--;
                if (phi->wCount == 0)
                {
                    // Useage count went to zero so unlink it and delete it
                    if (phiPrev != NULL)
                        phiPrev->phiNext = phi->phiNext;
                    else
                        pht->ahiBuckets[wBucket] = phi->phiNext;

                    // And delete it
                    Free(phi);

                    phi = NULL;
                }
            }
        
            case LOOKUPHASHITEM:
                pht->phiLast = phi;
                break;
        }

        LEAVECRITICAL;
    }
    else
    {
        phi = NULL;
    }
    
    // If find was passed in simply return it.
    return phi ? (LPCSTR)phi->szName : NULL;
}

//--------------------------------------------------------------------------

LPCSTR WINAPI AddHashItem(PHASHTABLE pht, LPCSTR lpszStr)
{
    return LookupItemInHashTable(pht, lpszStr, ADDHASHITEM);
}

//--------------------------------------------------------------------------

LPCSTR WINAPI DeleteHashItem(PHASHTABLE pht, LPCSTR lpszStr)
{
    return LookupItemInHashTable(pht, lpszStr, DELETEHASHITEM);
}

//======================================================================

PHASHTABLE WINAPI CreateHashItemTable(UINT wBuckets, UINT wExtra, BOOL fCaseSensitive)
{
    PHASHTABLE pht;

    if (wBuckets == 0)
        wBuckets = 71;

    pht = (PHASHTABLE)Alloc(sizeof(HASHTABLE) + wBuckets * sizeof(PHASHITEM));

    if (pht) {
        pht->fUpperCase = !fCaseSensitive;
        pht->wBuckets = wBuckets;
        pht->wcbExtra = wExtra;
    }
    
    return pht;    
}

//======================================================================

PHASHTABLE NEAR PASCAL GetGlobalHashTable()
{
    if (g_pHashTable == NULL) {
        g_pHashTable = CreateHashItemTable(71, 0, FALSE);
    }
    return g_pHashTable;
}