windows-nt-4.0/private/mvdm/wow32/walloc16.c

//*****************************************************************************
//
// MESSAGE HEAP 16 -
//
//     Heap allocation functions for 32-16 message thunks.
//
//     NOTE: these are NOT general purpose heap managment routines.
//
//
// 07-17-92  NanduriR   Created.
//
//*****************************************************************************

#include "precomp.h"
#pragma hdrstop

MODNAME(walloc16.c);

//*****************************************************************************
// General Notes:
//
// This heap maanger is for specific 'performance gains' and is thus not
// intended for general purpose use and therfore much of the overhead has
// been eliminated.
//
// This heap manager is intended mainly for thunks - where we are sure that
// an alloced block will definitely be freed. Thus it is meant for our use.
//
// The heap is conceptually an array  of constant-size blocks. The size of the
// block is predefined. The code is optimized for allocation requests of one
// blocksize or less. It is slower if the allocation request needs more than
// one block.
//
// The heap header is a static array. The header has two flags. One to note
// that a particular heapblock is in use and the other to note whether the
// block forms a part of a linked/chained set of contiguous blocks. The blocks
// are linked when the allocation request is for more than the predefined
// block size.
//
//*****************************************************************************


#define HEAP16_TOTALSIZE  0x2000
#define HEAP16_BLOCKSIZE  0x100    // We should set it to an optimum value
#define HEAP16_BLOCKCOUNT (HEAP16_TOTALSIZE/HEAP16_BLOCKSIZE)

#define HHDR16_FINUSE     0x01
#define HHDR16_FLINKED    0x02

#define ISBLOCKINUSE(block)    ((block) & HHDR16_FINUSE)
#define ISBLOCKLINKED(block) ((block) & HHDR16_FLINKED)


//*****************************************************************************
//
// Globals -
//
// vahdr - is the heap header. This header is 32bit memory and not part of the
//         16bit heap - this is so that the 16bit heap is put to maximum use.
//
// vpHeap16 - far pointer to the start of 16bit heap
//
// viFreeIndex - the index from which we start searching for a freeblock.
//               Normally this is set to the memoryblock that was most
//               recently freed, thus increasing the chances of finding
//               a freeblock instantly.
//*****************************************************************************

BYTE    vahdr[HEAP16_BLOCKCOUNT];
LPBYTE  vpHeap16 = (LPBYTE)NULL;
UINT    viFreeIndex = 0;            // First look for Free block here.



//*****************************************************************************
//
// malloc16 -
//
//      Allocs memory from 16bit block.
//      If heap is full, does normal GlobalAlloc
//
//      Returns farpointer to memoryblock;
//
//*****************************************************************************

VPVOID FASTCALL malloc16(UINT cb)
{
    INT i, j;
    INT cBlocksRequired;
    INT fContiguousFreeBlocks;
    INT vpT;

    if (vpHeap16 == (LPBYTE)NULL) {
        vpHeap16 = (LPBYTE)GlobalAllocLock16(GMEM_MOVEABLE | GMEM_SHARE, HEAP16_TOTALSIZE,
                                                                         NULL);
        if (vpHeap16 != NULL) {

            //
            // Initialize heap header.
            // LATER: is this necessary?. Heaphdr is a static array so
            //        is it already intialized to ZERO?
            //

            for(i = 0; i < HEAP16_BLOCKCOUNT ; i++) {
                vahdr[i] = 0;
            }

        }

    }

    if (vpHeap16 != (LPBYTE)NULL) {
        if (cb <= HEAP16_BLOCKSIZE && !ISBLOCKINUSE(vahdr[viFreeIndex])) {

            //
            // If 'single' block and the 'current' index is free.
            //

            vahdr[viFreeIndex] = HHDR16_FINUSE;
            i = viFreeIndex++;
            if (viFreeIndex == HEAP16_BLOCKCOUNT)
                viFreeIndex = 0;
            return (VPVOID)((LPBYTE)vpHeap16 + i * HEAP16_BLOCKSIZE);
        }
        else {

            //
            // if the 'current' index is not free or if 'multiple' blocks
            //

            cBlocksRequired = (cb / HEAP16_BLOCKSIZE) + 1;
            for (i = 0; i < HEAP16_BLOCKCOUNT ; i++ ) {
                 if ((viFreeIndex + i + cBlocksRequired) <=
                                                          HEAP16_BLOCKCOUNT) {
                     fContiguousFreeBlocks = TRUE;
                     for (j = 0; j < cBlocksRequired; j++) {
                         if (ISBLOCKINUSE(vahdr[viFreeIndex + i + j])) {
                             fContiguousFreeBlocks = FALSE;
                             i += j;
                             break;
                         }
                     }

                     if (fContiguousFreeBlocks) {
                         for (j = 0; j < (cBlocksRequired - 1); j++) {
                              vahdr[viFreeIndex + i + j] =
                                             (HHDR16_FINUSE |  HHDR16_FLINKED);
                         }
                         vahdr[viFreeIndex + i + j] = HHDR16_FINUSE;

                         i += viFreeIndex;
                         viFreeIndex = i + cBlocksRequired;
                         if (viFreeIndex == HEAP16_BLOCKCOUNT)
                             viFreeIndex = 0;
                         return (VPVOID)((LPBYTE)vpHeap16 + i * HEAP16_BLOCKSIZE);
                     }
                 }
                 else {

                     //
                     // Outside the heaphdr range. Reset viFreeIndex, so that
                     // we search from the start of heaphdr.
                     //

                     viFreeIndex = -(i+1);
                 }
            }
            viFreeIndex = 0;
        }

    }

    //
    // Here - if allocation from heap failed
    //

    vpT = (VPVOID)GlobalAllocLock16(GMEM_MOVEABLE, cb, NULL);
    if (vpT) {
        return vpT;
    }
    else {
        LOGDEBUG(0,("malloc16: failed\n"));
        return (VPVOID)NULL;
    }
}



//*****************************************************************************
//
// free16 -
//
//      frees 16bit memory block.
//      If the block is not part of the 16bit heap, does GlobalFree.
//
//      Returns TRUE;
//
//*****************************************************************************

BOOL FASTCALL free16(VPVOID vp)
{
    INT iStartIndex;
    BOOL fLinked;

    iStartIndex = ((LPBYTE)vp - (LPBYTE)vpHeap16) / HEAP16_BLOCKSIZE;

    //
    // Invalid iStartIndex implies that the block was GlobalAlloced
    //

    if (iStartIndex >= 0 && iStartIndex < HEAP16_BLOCKCOUNT) {

        //
        // If   'single'   block: get out fast
        // else 'multiple' block: loop for all the blocks
        //

        viFreeIndex = iStartIndex;
        if (!ISBLOCKLINKED(vahdr[iStartIndex])) {
            WOW32ASSERT(ISBLOCKINUSE(vahdr[iStartIndex]));
            vahdr[iStartIndex] = 0;
        }
        else {
            while (ISBLOCKINUSE(vahdr[iStartIndex])) {
                fLinked = ISBLOCKLINKED(vahdr[iStartIndex]);
                vahdr[iStartIndex] = 0;
                if (fLinked)
                    iStartIndex++;
                else
                    break;
            }
        }
    }
    else {
        WOW32ASSERT(LOWORD(vp)==0);  // GlobalAlloced pointers have offset = 0
        GlobalUnlockFree16(vp);
    }
    return (BOOL)TRUE;
}


//*****************************************************************************
//
// stackalloc16 -
//
//      Allocs memory from current task's 16bit stack.
//      Returns farpointer to memoryblock;
//
//*****************************************************************************

VPVOID FASTCALL stackalloc16(UINT cb)
{
    register PTD ptd;

    // get current task's 16bit stack

    ptd = CURRENTPTD();

    // grow ss:sp and return this imaginary pointer.

    if (ptd->dwFlags & TDF_INITCALLBACKSTACK) {
        ptd->vpCBStack = ptd->vpStack - cb;
        ptd->dwFlags &= ~TDF_INITCALLBACKSTACK;
    }
    else {
        ptd->vpCBStack -= cb;
    }

    return (VPVOID)ptd->vpCBStack;
}