reactos/boot/environ/lib/misc/util.c

   1 /*
   2  * COPYRIGHT:       See COPYING.ARM in the top level directory
   3  * PROJECT:         ReactOS UEFI Boot Library
   4  * FILE:            boot/environ/lib/misc/util.c
   5  * PURPOSE:         Boot Library Utility Functions
   6  * PROGRAMMER:      Alex Ionescu (alex.ionescu@reactos.org)
   7  */
   8
   9 /* INCLUDES ******************************************************************/
  10
  11 #include "bl.h"
  12
  13 /* DATA VARIABLES ************************************************************/
  14
  15 PRSDT UtlRsdt;
  16 PXSDT UtlXsdt;
  17
  18 PVOID UtlMcContext;
  19 PVOID UtlMcDisplayMessageRoutine;
  20 PVOID UtlMcUpdateMessageRoutine;
  21
  22 PVOID UtlProgressRoutine;
  23 PVOID UtlProgressContext;
  24 PVOID UtlProgressInfoRoutine;
  25 ULONG UtlProgressGranularity;
  26 ULONG UtlCurrentPercentComplete;
  27 ULONG UtlNextUpdatePercentage;
  28 BOOLEAN UtlProgressNeedsInfoUpdate;
  29 PVOID UtlProgressInfo;
  30
  31
  32
  33 /* FUNCTIONS *****************************************************************/
  34
  35 NTSTATUS
  36 BlUtlGetAcpiTable (
  37     _Out_ PVOID* TableAddress,
  38     _In_ ULONG Signature
  39     )
  40 {
  41     ULONG i, TableCount, HeaderLength;
  42     NTSTATUS Status;
  43     PRSDT Rsdt;
  44     PXSDT Xsdt;
  45     PHYSICAL_ADDRESS PhysicalAddress;
  46     PDESCRIPTION_HEADER Header;
  47
  48     Header = 0;
  49
  50     /* Make sure there's an output parameter */
  51     if (!TableAddress)
  52     {
  53         return STATUS_INVALID_PARAMETER;
  54     }
  55
  56     /* Get the currently known RSDT and XSDT */
  57     Rsdt = (PRSDT)UtlRsdt;
  58     Xsdt = (PXSDT)UtlXsdt;
  59
  60     /* Is there an RSDT? */
  61     if (!Rsdt)
  62     {
  63         /* No -- is there an XSDT? */
  64         if (!Xsdt)
  65         {
  66             /* No. Look up the RSDT */
  67             Status = EfipGetRsdt(&PhysicalAddress);
  68             if (!NT_SUCCESS(Status))
  69             {
  70                 EfiPrintf(L"no rsdp found\r\n");
  71                 return Status;
  72             }
  73
  74             /* Map the header */
  75             Status = BlMmMapPhysicalAddressEx((PVOID)&Header,
  76                                               0,
  77                                               sizeof(*Header),
  78                                               PhysicalAddress);
  79             if (!NT_SUCCESS(Status))
  80             {
  81                 return Status;
  82             }
  83
  84             /* Unmap the header */
  85             BlMmUnmapVirtualAddressEx(Header, sizeof(*Header));
  86
  87             /* Map the whole table */
  88             Status = BlMmMapPhysicalAddressEx((PVOID)&Header,
  89                                               0,
  90                                               Header->Length,
  91                                               PhysicalAddress);
  92             if (!NT_SUCCESS(Status))
  93             {
  94                 return Status;
  95             }
  96
  97             /* Check if its an XSDT or an RSDT */
  98             if (Header->Signature == XSDT_SIGNATURE)
  99             {
 100                 /* It's an XSDT */
 101                 Xsdt = (PXSDT)Header;
 102                 UtlXsdt = Xsdt;
 103             }
 104             else
 105             {
 106                 /* It's an RSDT */
 107                 Rsdt = (PRSDT)Header;
 108                 UtlRsdt = Rsdt;
 109             }
 110         }
 111     }
 112
 113     /* OK, so do we have an XSDT after all? */
 114     if (Xsdt)
 115     {
 116         /* Yes... how big is it? */
 117         HeaderLength = Xsdt->Header.Length;
 118         if (HeaderLength >= sizeof(*Header))
 119         {
 120             HeaderLength = sizeof(*Header);
 121         }
 122
 123         /* Based on that, how many tables are there? */
 124         TableCount = (Xsdt->Header.Length - HeaderLength) / sizeof(PHYSICAL_ADDRESS);
 125     }
 126     else
 127     {
 128         /* Nope, we have an RSDT. How big is it? */
 129         HeaderLength = Rsdt->Header.Length;
 130         if (HeaderLength >= sizeof(*Header))
 131         {
 132             HeaderLength = sizeof(*Header);
 133         }
 134
 135         /* Based on that, how many tables are there? */
 136         TableCount = (Rsdt->Header.Length - HeaderLength) / sizeof(ULONG);
 137     }
 138
 139     /* Loop through the ACPI tables */
 140     for (i = 0; i < TableCount; i++)
 141     {
 142         /* For an XSDT, read the 64-bit address directly */
 143         if (Xsdt)
 144         {
 145             PhysicalAddress = Xsdt->Tables[i];
 146         }
 147         else
 148         {
 149             /* For RSDT, cast it */
 150             PhysicalAddress.QuadPart = Rsdt->Tables[i];
 151         }
 152
 153         /* Map the header */
 154         Status = BlMmMapPhysicalAddressEx((PVOID)&Header,
 155                                           0,
 156                                           sizeof(*Header),
 157                                           PhysicalAddress);
 158         if (!NT_SUCCESS(Status))
 159         {
 160             return Status;
 161         }
 162
 163         /* Is it the right one? */
 164         if (Header->Signature == Signature)
 165         {
 166             /* Unmap the header */
 167             BlMmUnmapVirtualAddressEx(Header, sizeof(*Header));
 168
 169             /* Map the whole table */
 170             return BlMmMapPhysicalAddressEx(TableAddress,
 171                                             0,
 172                                             Header->Length,
 173                                             PhysicalAddress);
 174         }
 175     }
 176
 177     /* Requested table does not exist */
 178     return STATUS_NOT_FOUND;
 179 }
 180
 181
 182 VOID
 183 BlUtlUpdateProgress (
 184     _In_ ULONG Percentage,
 185     _Out_opt_ PBOOLEAN Completed
 186     )
 187 {
 188     if (UtlProgressRoutine)
 189     {
 190         EfiPrintf(L"Unimplemented\r\n");
 191     }
 192     else if (*Completed)
 193     {
 194         *Completed = TRUE;
 195     }
 196 }
 197
 198 NTSTATUS
 199 BlUtlInitialize (
 200     VOID
 201     )
 202 {
 203     UtlRsdt = 0;
 204     UtlXsdt = 0;
 205
 206     UtlMcContext = 0;
 207     UtlMcDisplayMessageRoutine = 0;
 208     UtlMcUpdateMessageRoutine = 0;
 209
 210     UtlProgressRoutine = 0;
 211     UtlProgressContext = 0;
 212     UtlProgressInfoRoutine = 0;
 213     UtlProgressGranularity = 0;
 214     UtlCurrentPercentComplete = 0;
 215     UtlNextUpdatePercentage = 0;
 216     UtlProgressNeedsInfoUpdate = 0;
 217     UtlProgressInfo = 0;
 218
 219     return STATUS_SUCCESS;
 220 }
 221
 222 VOID
 223 BmUpdateProgressInfo (
 224     _In_ PVOID Unknown,
 225     _In_ PWCHAR ProgressInfo
 226     )
 227 {
 228     EfiPrintf(L"Progress Info: %s\r\n", ProgressInfo);
 229 }
 230
 231 VOID
 232 BmUpdateProgress (
 233     _In_ PVOID Unknown,
 234     _In_ ULONG Percent,
 235     _Out_ PBOOLEAN Completed
 236     )
 237 {
 238     EfiPrintf(L"Progress: %d\r\n", Percent);
 239     if (Completed)
 240     {
 241         *Completed = TRUE;
 242     }
 243 }
 244
 245 NTSTATUS
 246 BlUtlRegisterProgressRoutine (
 247     VOID
 248     )
 249 {
 250     /* One shouldn't already exist */
 251     if (UtlProgressRoutine)
 252     {
 253         return STATUS_UNSUCCESSFUL;
 254     }
 255
 256     /* Set the routine, and no context */
 257     UtlProgressRoutine = BmUpdateProgress;
 258     UtlProgressContext = NULL;
 259
 260     /* Progress increases by one */
 261     UtlProgressGranularity = 1;
 262
 263     /* Set progress to zero for now */
 264     UtlCurrentPercentComplete = 0;
 265     UtlNextUpdatePercentage = 0;
 266
 267     /* Set the info routine if there is one */
 268     UtlProgressInfoRoutine = BmUpdateProgressInfo;
 269
 270     /* All good */
 271     return STATUS_SUCCESS;
 272 }
 273
 274 PVOID
 275 BlTblFindEntry (
 276     _In_ PVOID *Table,
 277     _In_ ULONG Count,
 278     _Out_ PULONG EntryIndex,
 279     _In_ PBL_TBL_LOOKUP_ROUTINE Callback,
 280     _In_ PVOID Argument1,
 281     _In_ PVOID Argument2,
 282     _In_ PVOID Argument3,
 283     _In_ PVOID Argument4
 284     )
 285 {
 286     PVOID Entry = NULL;
 287     ULONG Index;
 288     BOOLEAN Result;
 289
 290     /* Check for invalid parameters */
 291     if (!(Table) || !(EntryIndex))
 292     {
 293         return Entry;
 294     }
 295
 296     /* Loop each entry in the table */
 297     for (Index = 0; Index < Count;  Index++)
 298     {
 299         /* Check if this entry is filled out */
 300         if (Table[Index])
 301         {
 302             /* Call the comparison function */
 303             Result = Callback(Table[Index],
 304                               Argument1,
 305                               Argument2,
 306                               Argument3,
 307                               Argument4);
 308             if (Result)
 309             {
 310                 /* Entry found return it */
 311                 *EntryIndex = Index;
 312                 Entry = Table[Index];
 313                 break;
 314             }
 315         }
 316     }
 317
 318     /* Return the entry that was (or wasn't) found */
 319     return Entry;
 320 }
 321
 322 NTSTATUS
 323 BlTblSetEntry (
 324     _Inout_ PVOID** Table,
 325     _Inout_ PULONG Count,
 326     _In_ PVOID Entry,
 327     _Out_ PULONG EntryIndex,
 328     _In_ PBL_TBL_SET_ROUTINE Callback
 329     )
 330 {
 331     ULONG NewCount;
 332     NTSTATUS Status = STATUS_SUCCESS;
 333     ULONG Index = 0;
 334     PVOID* NewTable;
 335
 336     /* Make sure all the parameters were specified */
 337     if (!(Table) || !(*Table) || !(Count) || !(Callback))
 338     {
 339         return STATUS_INVALID_PARAMETER;
 340     }
 341
 342     /* Read the current table */
 343     NewTable = *Table;
 344     NewCount = *Count;
 345
 346     /* Iterate over it */
 347     while (Index < NewCount)
 348     {
 349         /* Look for a free index */
 350         if (!NewTable[Index])
 351         {
 352             goto SetIndex;
 353         }
 354
 355         /* No free index yet, keep going */
 356         ++Index;
 357     }
 358
 359     /* No free index was found, try to purge some entries */
 360     Index = 0;
 361     while (Index < NewCount)
 362     {
 363         /* Call each purge callback, trying to make space */
 364         Status = Callback(NewTable[Index]);
 365         if (NT_SUCCESS(Status))
 366         {
 367             /* We should have this slot available now */
 368             goto SetIndex;
 369         }
 370
 371         /* Keep trying to purge more */
 372         ++Index;
 373     }
 374
 375     /* Double the table */
 376     NewTable = BlMmAllocateHeap(2 * sizeof(PVOID) * NewCount);
 377     if (!NewTable)
 378     {
 379         return STATUS_NO_MEMORY;
 380     }
 381
 382     /* Clear the new table, and copy the old entries */
 383     RtlZeroMemory(&NewTable[NewCount], sizeof(PVOID) * NewCount);
 384     RtlCopyMemory(NewTable, *Table, sizeof(PVOID) * NewCount);
 385
 386     /* Free the old table */
 387     BlMmFreeHeap(*Table);
 388
 389     /* Return the new table and count */
 390     *Count = 2 * NewCount;
 391     *Table = NewTable;
 392
 393 SetIndex:
 394     /* Set the index and return */
 395     NewTable[Index] = Entry;
 396     *EntryIndex = Index;
 397     return Status;
 398 }
 399
 400 NTSTATUS
 401 BlTblMap (
 402     _In_ PVOID *Table,
 403     _In_ ULONG Count,
 404     _In_ PBL_TBL_MAP_ROUTINE MapCallback
 405     )
 406 {
 407     NTSTATUS Status, LocalStatus;
 408     PVOID Entry;
 409     ULONG Index;
 410
 411     /* Bail out if there's no table */
 412     if (!Table)
 413     {
 414         return STATUS_INVALID_PARAMETER;
 415     }
 416
 417     /* Assume success and loop each index */
 418     Status = STATUS_SUCCESS;
 419     for (Index = 0; Index < Count; Index++)
 420     {
 421         /* See if an entry exists at this index */
 422         Entry = Table[Index];
 423         if (Entry)
 424         {
 425             /* Call the map routine for this entry */
 426             LocalStatus = MapCallback(Entry, Index);
 427             if (!NT_SUCCESS(LocalStatus))
 428             {
 429                 /* Propagate failure only */
 430                 Status = LocalStatus;
 431             }
 432         }
 433     }
 434
 435     /* Return status to caller */
 436     return Status;
 437 }
 438
 439 ULONG HtTableSize;
 440 PBL_HASH_TABLE* HtTableArray;
 441 ULONG HtTableEntries;
 442
 443 ULONG
 444 DefaultHashFunction (
 445     _In_ PBL_HASH_ENTRY Entry,
 446     _In_ ULONG TableSize
 447     )
 448 {
 449     PUCHAR Value;
 450     ULONG KeyHash, i;
 451
 452     /* Check if the value is a pointer, or embedded inline */
 453     Value = (Entry->Flags & BL_HT_VALUE_IS_INLINE) ? Entry->Value : (PUCHAR)&Entry->Value;
 454
 455     /* Iterate over each byte, and sum it */
 456     for (i = 0, KeyHash = 0; i < Entry->Size; i++)
 457     {
 458         KeyHash += Value[i++];
 459     }
 460
 461     /* Modulo the number of buckets */
 462     return KeyHash % TableSize;
 463 }
 464
 465 BOOLEAN
 466 HtpCompareKeys (
 467     _In_ PBL_HASH_ENTRY Entry1,
 468     _In_ PBL_HASH_ENTRY Entry2
 469     )
 470 {
 471     ULONG Flags;
 472     BOOLEAN ValueMatch;
 473
 474     /* Check if the flags or sizes are not matching */
 475     Flags = Entry1->Flags;
 476     if ((Entry1->Size != Entry2->Size) || (Flags != Entry2->Flags))
 477     {
 478         ValueMatch = FALSE;
 479     }
 480     else if (Flags & BL_HT_VALUE_IS_INLINE)
 481     {
 482         /* Check if this is an in-line value, compare it */
 483         ValueMatch = Entry1->Value == Entry2->Value;
 484     }
 485     else
 486     {
 487         /* This is a pointer value, compare it */
 488         ValueMatch = (RtlCompareMemory(Entry1->Value, Entry2->Value, Entry1->Size) ==
 489                       Entry1->Size);
 490     }
 491
 492     /* Return if it matched */
 493     return ValueMatch;
 494 }
 495
 496 NTSTATUS
 497 TblDoNotPurgeEntry (
 498     _In_ PVOID Entry
 499     )
 500 {
 501     /* Never purge this entry */
 502     return STATUS_UNSUCCESSFUL;
 503 }
 504
 505 NTSTATUS
 506 BlHtCreate (
 507     _In_ ULONG Size,
 508     _In_ PBL_HASH_TABLE_HASH_FUNCTION HashFunction,
 509     _In_ PBL_HASH_TABLE_COMPARE_FUNCTION CompareFunction,
 510     _Out_ PULONG Id
 511     )
 512 {
 513     NTSTATUS Status;
 514     PBL_HASH_TABLE HashTable;
 515     ULONG i;
 516
 517     /* Assume failure */
 518     HashTable = NULL;
 519
 520     /* Can't create a table with no ID */
 521     if (!Id)
 522     {
 523         return STATUS_INVALID_PARAMETER;
 524     }
 525
 526     /* Check if we don't already have a hash table table */
 527     if (!HtTableSize)
 528     {
 529         /* Allocate it and zero it out */
 530         HtTableSize = 4;
 531         HtTableArray = BlMmAllocateHeap(HtTableSize * sizeof(PVOID));
 532         if (!HtTableArray)
 533         {
 534             Status = STATUS_NO_MEMORY;
 535             goto Quickie;
 536         }
 537         RtlZeroMemory(HtTableArray, HtTableSize * sizeof(PVOID));
 538         HtTableEntries = 0;
 539     }
 540
 541     /* Allocate the hash table */
 542     HashTable = BlMmAllocateHeap(sizeof(*HashTable));
 543     if (!HashTable)
 544     {
 545         Status = STATUS_NO_MEMORY;
 546         goto Quickie;
 547     }
 548
 549     /* Fill it out */
 550     HashTable->HashFunction = HashFunction ? HashFunction : DefaultHashFunction;
 551     HashTable->CompareFunction = CompareFunction ? CompareFunction : HtpCompareKeys;
 552     HashTable->Size = Size ? Size : 13;
 553
 554     /* Allocate the hash links, one for each bucket */
 555     HashTable->HashLinks = BlMmAllocateHeap(sizeof(LIST_ENTRY) * HashTable->Size);
 556     if (!HashTable->HashLinks)
 557     {
 558         Status = STATUS_NO_MEMORY;
 559         goto Quickie;
 560     }
 561
 562     /* Initialize the hash links */
 563     for (i = 0; i < HashTable->Size; i++)
 564     {
 565         InitializeListHead(&HashTable->HashLinks[i]);
 566     }
 567
 568     /* Save us in the table of hash tables */
 569     Status = BlTblSetEntry((PVOID**)&HtTableArray,
 570                            &Size,
 571                            HashTable,
 572                            Id,
 573                            TblDoNotPurgeEntry);
 574     if (NT_SUCCESS(Status))
 575     {
 576         /* One more -- we're done */
 577         ++HtTableEntries;
 578         return Status;
 579     }
 580
 581 Quickie:
 582     /* Check if we just allocated the table array now */
 583     if (!(HtTableEntries) && (HtTableArray))
 584     {
 585         /* Free it */
 586         BlMmFreeHeap(HtTableArray);
 587         HtTableArray = NULL;
 588         HtTableSize = 0;
 589     }
 590
 591     /* Check if we allocated a hash table*/
 592     if (HashTable)
 593     {
 594         /* With links? */
 595         if (HashTable->HashLinks)
 596         {
 597             /* Free them */
 598             BlMmFreeHeap(HashTable->HashLinks);
 599         }
 600
 601         /* Free the table*/
 602         BlMmFreeHeap(HashTable);
 603     }
 604
 605     /* We're done */
 606     return Status;
 607 }
 608
 609 NTSTATUS
 610 BlHtLookup (
 611     _In_ ULONG TableId,
 612     _In_ PBL_HASH_ENTRY Entry,
 613     _Out_opt_ PBL_HASH_VALUE *Value
 614     )
 615 {
 616     PBL_HASH_TABLE HashTable;
 617     ULONG HashValue;
 618     NTSTATUS Status;
 619     PLIST_ENTRY HashLinkHead, HashLink;
 620     PBL_HASH_NODE HashNode;
 621
 622     /* Check if the table ID is invalid, or we have no entry, or it's malformed */
 623     if ((HtTableSize <= TableId) ||
 624         !(Entry) ||
 625         ((Entry->Flags & BL_HT_VALUE_IS_INLINE) && (Entry->Size != sizeof(ULONG))))
 626     {
 627         /* Fail */
 628         Status = STATUS_INVALID_PARAMETER;
 629     }
 630     else
 631     {
 632         /* Otherwise, get the hash table for this index */
 633         HashTable = HtTableArray[TableId];
 634
 635         /* Get the hash bucket */
 636         HashValue = HashTable->HashFunction(Entry, HashTable->Size);
 637
 638         /* Start iterating each entry in the bucket, assuming failure */
 639         Status = STATUS_NOT_FOUND;
 640         HashLinkHead = &HashTable->HashLinks[HashValue];
 641         HashLink = HashLinkHead->Flink;
 642         while (HashLink != HashLinkHead)
 643         {
 644             /* Get a node in this bucket, and compare the value */
 645             HashNode = CONTAINING_RECORD(HashLink, BL_HASH_NODE, ListEntry);
 646             if (HashTable->CompareFunction(&HashNode->Entry, Entry))
 647             {
 648                 /* Does the caller want the value? */
 649                 if (Value)
 650                 {
 651                     /* Return it */
 652                     *Value = &HashNode->Value;
 653                 }
 654
 655                 /* Return success and stop scanning */
 656                 Status = STATUS_SUCCESS;
 657                 break;
 658             }
 659
 660             /* Try the next node */
 661             HashLink = HashLink->Flink;
 662         }
 663     }
 664
 665     /* Return back to the caller */
 666     return Status;
 667 }
 668
 669 NTSTATUS
 670 BlHtStore (
 671     _In_ ULONG TableId,
 672     _In_ PBL_HASH_ENTRY Entry,
 673     _In_ PVOID Data,
 674     _In_ ULONG DataSize
 675     )
 676 {
 677     PBL_HASH_NODE HashNode;
 678     NTSTATUS Status;
 679     PLIST_ENTRY HashLinkHead;
 680     PBL_HASH_TABLE HashTable;
 681
 682     /* Check for invalid table ID, missing arguments, or malformed entry */
 683     if ((HtTableSize <= TableId) ||
 684         !(Entry) ||
 685         !(Data) ||
 686         !(Entry->Size) ||
 687         !(Entry->Value) ||
 688         !(DataSize) ||
 689         ((Entry->Flags & BL_HT_VALUE_IS_INLINE) && (Entry->Size != sizeof(ULONG))))
 690     {
 691         /* Fail the call */
 692         Status = STATUS_INVALID_PARAMETER;
 693         goto Quickie;
 694     }
 695
 696     /* Get the hash table for this ID */
 697     HashTable = HtTableArray[TableId];
 698
 699     /* Allocate a hash node */
 700     HashNode = BlMmAllocateHeap(sizeof(*HashNode));
 701     if (!HashNode)
 702     {
 703         Status = STATUS_NO_MEMORY;
 704         goto Quickie;
 705     }
 706
 707     /* Capture all the data*/
 708     HashNode->Entry.Size = Entry->Size;
 709     HashNode->Entry.Flags = Entry->Flags;
 710     HashNode->Entry.Value = Entry->Value;
 711     HashNode->Value.DataSize = DataSize;
 712     HashNode->Value.Data = Data;
 713
 714     /* Insert it into the bucket list and return success */
 715     HashLinkHead = &HashTable->HashLinks[HashTable->HashFunction(Entry, HashTable->Size)];
 716     InsertTailList(HashLinkHead, &HashNode->ListEntry);
 717     Status = STATUS_SUCCESS;
 718
 719 Quickie:
 720     return Status;
 721 }
 722
 723 ULONG
 724 BlUtlCheckSum (
 725     _In_ ULONG PartialSum,
 726     _In_ PUCHAR Buffer,
 727     _In_ ULONG Length,
 728     _In_ ULONG Flags
 729     )
 730 {
 731     ULONG i;
 732
 733     if (Flags & BL_UTL_CHECKSUM_UCHAR_BUFFER)
 734     {
 735         EfiPrintf(L"Not supported\r\n");
 736         return 0;
 737     }
 738     else if (Flags & BL_UTL_CHECKSUM_USHORT_BUFFER)
 739     {
 740         PartialSum = (unsigned __int16)PartialSum;
 741         Length &= ~1;
 742
 743         for (i = 0; i < Length; i += 2)
 744         {
 745             PartialSum += *(unsigned __int16 *)&Buffer[i];
 746             if (Flags & BL_UTL_CHECKSUM_COMPLEMENT)
 747             {
 748                 PartialSum = (unsigned __int16)((PartialSum >> 16) + PartialSum);
 749             }
 750         }
 751
 752         if (i != Length)
 753         {
 754             PartialSum += (unsigned __int8)Buffer[Length];
 755             if (Flags & BL_UTL_CHECKSUM_COMPLEMENT)
 756             {
 757                 PartialSum = (unsigned __int16)((PartialSum >> 16) + PartialSum);
 758             }
 759         }
 760
 761         if (Flags & BL_UTL_CHECKSUM_NEGATE)
 762         {
 763             return ~PartialSum;
 764         }
 765
 766         PartialSum = (unsigned __int16)PartialSum;
 767     }
 768     else
 769     {
 770         /* Invalid mode */
 771         return 0;
 772     }
 773
 774     if (Flags & BL_UTL_CHECKSUM_NEGATE)
 775     {
 776         return ~PartialSum;
 777     }
 778
 779     return PartialSum;
 780 }