17) ntdll!RtlpFindEntry()

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/*
 * ntdll.dll中定义的全局变量
 */
extern BYTE RtlpBitsClearLow[];

PLIST_ENTRY NTAPI RtlpFindEntry
(
    Heap,
    Size
)
{
    ListEntry;
    FreeEntry;
    Cache;
    Entries;
    Index;
    FreeEntryList;
    p;
    value;
    Teb;
    i;

    ListEntry   = &Heap->FreeLists[0];
    if ( ListEntry == ListEntry->Blink )
    {
        goto RtlpFindEntry_exit;
    }
    FreeEntry   = ( ListEntry->Blink - 8 );
    if ( FreeEntry->Entry.Size < Size )
    {
        goto RtlpFindEntry_exit;
    }
    FreeEntry   = ( ListEntry->Flink - 8 );
    if ( Size <= FreeEntry->Entry.Size )
    {
        ListEntry = ListEntry->Flink;
        goto RtlpFindEntry_exit;
    }
    Cache       = Heap->Cache;
    Entries     = Cache->Entries;
    Index       = Size - 128;
    if ( Index >= Entries )
    {
        Index = Entries - 1;
    }
    if ( Index == ( Entries - 1 ) )
    {
        FreeEntryList = &Cache->FreeEntryArray[Index]->List;
        while ( ListEntry != FreeEntryList )
        {
            FreeEntry       = ( FreeEntryList - 8 );
            if ( FreeEntry->Entry.Size >= Size )
            {
                ListEntry = FreeEntryList;
                goto RtlpFindEntry_exit;
            }
            FreeEntryList   = FreeEntryList->Flink;
        }  /* end of while */
    }
    p           = ( PDWORD )&Cache->Bitmap[ Index / 8 ];
    value       = ~( 1 << ( Size & 0x0000001F ) - 1 ) & *p;
    if ( 0 == value )
    {
        while ( ( Index / 32 ) <= ( Entries / 32 - 1 ) )
        {
            value   = *++p;
            Index  += 32;
            if ( 0 != value )
            {
                break;
            }
        }  /* end of while */
        if ( 0 == value )
        {
            Teb         = NtCurrentTeb();
            DbgPrint
            (
                "HEAP[%wZ]: ",
                ( ( PLDR_MODULE )Teb->Peb->Ldr->InLoadOrderModuleList.Flink )->BaseDllName
            );
            DbgPrint
            (
                "Index not found into the bitmap %08lx\n",
                Size
            );
            ListEntry   = &Heap->FreeLists[0];
            goto RtlpFindEntry_exit;
        }
    }
    if ( 0 != ( value & 0x0000FFFF ) )
    {
        if ( 0 != ( value & 0x000000FF ) )
        {
            i   = ( int )RtlpBitsClearLow[ value & 0x000000FF ];
        }
        else
        {
            i   = ( int )RtlpBitsClearLow[ ( value & 0x0000FF00 ) >> 8 ] + 8;
        }
    }
    else
    {
        if ( 0 != ( value & 0x00FF0000 ) )
        {
            i   = ( int )RtlpBitsClearLow[ ( value & 0x00FF0000 ) >> 16 ] + 16;
        }
        else
        {
            i   = ( int )RtlpBitsClearLow[ value >> 24 ] + 24;
        }
    }
    Index      += ( DWORD )i;
    ListEntry   = &Cache->FreeEntryArray[Index]->List;

RtlpFindEntry_exit:

    return( ListEntry );
}  /* end of RtlpFindEntry */
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