path: root/MdePkg/Library/UefiLib/UefiLib.c

/** @file
  The UEFI Library provides functions and macros that simplify the development of 
  UEFI Drivers and UEFI Applications.  These functions and macros help manage EFI 
  events, build simple locks utilizing EFI Task Priority Levels (TPLs), install 
  EFI Driver Model related protocols, manage Unicode string tables for UEFI Drivers, 
  and print messages on the console output and standard error devices.

  Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>
  This program and the accompanying materials
  are licensed and made available under the terms and conditions of the BSD License
  which accompanies this distribution.  The full text of the license may be found at
  http://opensource.org/licenses/bsd-license.php.

  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.

**/


#include "UefiLibInternal.h"

/**
  Empty constructor function that is required to resolve dependencies between 
  libraries.
  
    ** DO NOT REMOVE **
  
  @param  ImageHandle   The firmware allocated handle for the EFI image.
  @param  SystemTable   A pointer to the EFI System Table.
  
  @retval EFI_SUCCESS   The constructor executed correctly.

**/
EFI_STATUS
EFIAPI
UefiLibConstructor (
  IN EFI_HANDLE        ImageHandle,
  IN EFI_SYSTEM_TABLE  *SystemTable
  )
{
  return EFI_SUCCESS;
}

/**
  Compare whether two names of languages are identical.

  @param  Language1 Name of language 1.
  @param  Language2 Name of language 2.

  @retval TRUE      Language 1 and language 2 are the same.
  @retval FALSE     Language 1 and language 2 are not the same.

**/
BOOLEAN
CompareIso639LanguageCode (
  IN CONST CHAR8  *Language1,
  IN CONST CHAR8  *Language2
  )
{
  UINT32  Name1;
  UINT32  Name2;

  Name1 = ReadUnaligned24 ((CONST UINT32 *) Language1);
  Name2 = ReadUnaligned24 ((CONST UINT32 *) Language2);

  return (BOOLEAN) (Name1 == Name2);
}

/**
  Retrieves a pointer to the system configuration table from the EFI System Table
  based on a specified GUID.
  
  This function searches the list of configuration tables stored in the EFI System Table
  for a table with a GUID that matches TableGuid.  If a match is found, then a pointer to
  the configuration table is returned in Table., and EFI_SUCCESS is returned. If a matching GUID
  is not found, then EFI_NOT_FOUND is returned.
  If TableGuid is NULL, then ASSERT().
  If Table is NULL, then ASSERT().

  @param  TableGuid       The pointer to table's GUID type.
  @param  Table           The pointer to the table associated with TableGuid in the EFI System Table.

  @retval EFI_SUCCESS     A configuration table matching TableGuid was found.
  @retval EFI_NOT_FOUND   A configuration table matching TableGuid could not be found.

**/
EFI_STATUS
EFIAPI
EfiGetSystemConfigurationTable (
  IN  EFI_GUID  *TableGuid,
  OUT VOID      **Table
  )
{
  EFI_SYSTEM_TABLE  *SystemTable;
  UINTN             Index;

  ASSERT (TableGuid != NULL);
  ASSERT (Table != NULL);

  SystemTable = gST;
  *Table = NULL;
  for (Index = 0; Index < SystemTable->NumberOfTableEntries; Index++) {
    if (CompareGuid (TableGuid, &(SystemTable->ConfigurationTable[Index].VendorGuid))) {
      *Table = SystemTable->ConfigurationTable[Index].VendorTable;
      return EFI_SUCCESS;
    }
  }

  return EFI_NOT_FOUND;
}

/**
  Creates and returns a notification event and registers that event with all the protocol
  instances specified by ProtocolGuid.

  This function causes the notification function to be executed for every protocol of type
  ProtocolGuid instance that exists in the system when this function is invoked. If there are
  no instances of ProtocolGuid in the handle database at the time this function is invoked,
  then the notification function is still executed one time. In addition, every time a protocol
  of type ProtocolGuid instance is installed or reinstalled, the notification function is also
  executed. This function returns the notification event that was created. 
  If ProtocolGuid is NULL, then ASSERT().
  If NotifyTpl is not a legal TPL value, then ASSERT().
  If NotifyFunction is NULL, then ASSERT().
  If Registration is NULL, then ASSERT().


  @param  ProtocolGuid    Supplies GUID of the protocol upon whose installation the event is fired.
  @param  NotifyTpl       Supplies the task priority level of the event notifications.
  @param  NotifyFunction  Supplies the function to notify when the event is signaled.
  @param  NotifyContext   The context parameter to pass to NotifyFunction.
  @param  Registration    A pointer to a memory location to receive the registration value.
                          This value is passed to LocateHandle() to obtain new handles that
                          have been added that support the ProtocolGuid-specified protocol. 

  @return The notification event that was created.

**/
EFI_EVENT
EFIAPI
EfiCreateProtocolNotifyEvent(
  IN  EFI_GUID          *ProtocolGuid,
  IN  EFI_TPL           NotifyTpl,
  IN  EFI_EVENT_NOTIFY  NotifyFunction,
  IN  VOID              *NotifyContext,  OPTIONAL
  OUT VOID              **Registration
  )
{
  EFI_STATUS  Status;
  EFI_EVENT   Event;

  ASSERT (ProtocolGuid != NULL);
  ASSERT (NotifyFunction != NULL);
  ASSERT (Registration != NULL);

  //
  // Create the event
  //

  Status = gBS->CreateEvent (
                  EVT_NOTIFY_SIGNAL,
                  NotifyTpl,
                  NotifyFunction,
                  NotifyContext,
                  &Event
                  );
  ASSERT_EFI_ERROR (Status);

  //
  // Register for protocol notifications on this event
  //

  Status = gBS->RegisterProtocolNotify (
                  ProtocolGuid,
                  Event,
                  Registration
                  );

  ASSERT_EFI_ERROR (Status);

  //
  // Kick the event so we will perform an initial pass of
  // current installed drivers
  //

  gBS->SignalEvent (Event);
  return Event;
}

/**
  Creates a named event that can be signaled with EfiNamedEventSignal().

  This function creates an event using NotifyTpl, NoifyFunction, and NotifyContext.
  This event is signaled with EfiNamedEventSignal(). This provides the ability for one or more
  listeners on the same event named by the GUID specified by Name. 
  If Name is NULL, then ASSERT().
  If NotifyTpl is not a legal TPL value, then ASSERT().
  If NotifyFunction is NULL, then ASSERT().

  @param  Name                  Supplies the GUID name of the event.
  @param  NotifyTpl             Supplies the task priority level of the event notifications.
  @param  NotifyFunction        Supplies the function to notify when the event is signaled.
  @param  NotifyContext         The context parameter to pass to NotifyFunction. 
  @param  Registration          A pointer to a memory location to receive the registration value.

  @retval EFI_SUCCESS           A named event was created.
  @retval EFI_OUT_OF_RESOURCES  There are not enough resource to create the named event.

**/
EFI_STATUS
EFIAPI
EfiNamedEventListen (
  IN CONST EFI_GUID    *Name,
  IN EFI_TPL           NotifyTpl,
  IN EFI_EVENT_NOTIFY  NotifyFunction,
  IN CONST VOID        *NotifyContext,  OPTIONAL
  OUT VOID             *Registration OPTIONAL
  )
{
  EFI_STATUS  Status;
  EFI_EVENT   Event;
  VOID        *RegistrationLocal;

  ASSERT (Name != NULL);
  ASSERT (NotifyFunction != NULL);
  ASSERT (NotifyTpl <= TPL_HIGH_LEVEL);
  
  //
  // Create event
  //
  Status = gBS->CreateEvent (
                  EVT_NOTIFY_SIGNAL,
                  NotifyTpl,
                  NotifyFunction,
                  (VOID *) NotifyContext,
                  &Event
                  );
  ASSERT_EFI_ERROR (Status);

  //
  // The Registration is not optional to RegisterProtocolNotify().
  // To make it optional to EfiNamedEventListen(), may need to substitute with a local.
  //
  if (Registration != NULL) {
    RegistrationLocal = Registration;
  } else {
    RegistrationLocal = &RegistrationLocal;
  }

  //
  // Register for an installation of protocol interface
  //

  Status = gBS->RegisterProtocolNotify (
                  (EFI_GUID *) Name,
                  Event,
                  RegistrationLocal
                  );
  ASSERT_EFI_ERROR (Status);

  return Status;
}

/**
  Signals a named event created with EfiNamedEventListen().

  This function signals the named event specified by Name. The named event must have been
  created with EfiNamedEventListen().
  If Name is NULL, then ASSERT().

  @param  Name                  Supplies the GUID name of the event.

  @retval EFI_SUCCESS           A named event was signaled.
  @retval EFI_OUT_OF_RESOURCES  There are not enough resource to signal the named event.

**/
EFI_STATUS
EFIAPI
EfiNamedEventSignal (
  IN CONST EFI_GUID  *Name
  )
{
  EFI_STATUS  Status;
  EFI_HANDLE  Handle;

  ASSERT(Name != NULL);

  Handle = NULL;
  Status = gBS->InstallProtocolInterface (
                  &Handle,
                  (EFI_GUID *) Name,
                  EFI_NATIVE_INTERFACE,
                  NULL
                  );
  ASSERT_EFI_ERROR (Status);

  Status = gBS->UninstallProtocolInterface (
                  Handle,
                  (EFI_GUID *) Name,
                  NULL
                  );
  ASSERT_EFI_ERROR (Status);

  return Status;
}

/**
  Signals an event group by placing a new event in the group temporarily and
  signaling it.

  @param[in] EventGroup          Supplies the unique identifier of the event
                                 group to signal.

  @retval EFI_SUCCESS            The event group was signaled successfully.
  @retval EFI_INVALID_PARAMETER  EventGroup is NULL.
  @return                        Error codes that report problems about event
                                 creation or signaling.
**/
EFI_STATUS
EFIAPI
EfiEventGroupSignal (
  IN CONST EFI_GUID *EventGroup
  )
{
  EFI_STATUS Status;
  EFI_EVENT  Event;

  if (EventGroup == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  Status = gBS->CreateEventEx (
                  EVT_NOTIFY_SIGNAL,
                  TPL_CALLBACK,
                  EfiEventEmptyFunction,
                  NULL,
                  EventGroup,
                  &Event
                  );
  if (EFI_ERROR (Status)) {
    return Status;
  }

  Status = gBS->SignalEvent (Event);
  gBS->CloseEvent (Event);

  return Status;
}

/**
  An empty function that can be used as NotifyFunction parameter of
  CreateEvent() or CreateEventEx().

  @param Event              Event whose notification function is being invoked.
  @param Context            The pointer to the notification function's context,
                            which is implementation-dependent.

**/
VOID
EFIAPI
EfiEventEmptyFunction (
  IN EFI_EVENT              Event,
  IN VOID                   *Context
  )
{
}

/** 
  Returns the current TPL.

  This function returns the current TPL.  There is no EFI service to directly 
  retrieve the current TPL. Instead, the RaiseTPL() function is used to raise 
  the TPL to TPL_HIGH_LEVEL.  This will return the current TPL.  The TPL level 
  can then immediately be restored back to the current TPL level with a call 
  to RestoreTPL().

  @return The current TPL.

**/
EFI_TPL
EFIAPI
EfiGetCurrentTpl (
  VOID
  )
{
  EFI_TPL Tpl;

  Tpl = gBS->RaiseTPL (TPL_HIGH_LEVEL);
  gBS->RestoreTPL (Tpl);

  return Tpl;
}


/**
  Initializes a basic mutual exclusion lock.

  This function initializes a basic mutual exclusion lock to the released state 
  and returns the lock.  Each lock provides mutual exclusion access at its task 
  priority level.  Since there is no preemption or multiprocessor support in EFI,
  acquiring the lock only consists of raising to the locks TPL.
  If Lock is NULL, then ASSERT().
  If Priority is not a valid TPL value, then ASSERT().

  @param  Lock       A pointer to the lock data structure to initialize.
  @param  Priority   EFI TPL is associated with the lock.

  @return The lock.

**/
EFI_LOCK *
EFIAPI
EfiInitializeLock (
  IN OUT EFI_LOCK  *Lock,
  IN EFI_TPL        Priority
  )
{
  ASSERT (Lock != NULL);
  ASSERT (Priority <= TPL_HIGH_LEVEL);

  Lock->Tpl       = Priority;
  Lock->OwnerTpl  = TPL_APPLICATION;
  Lock->Lock      = EfiLockReleased ;
  return Lock;
}

/**
  Acquires ownership of a lock.

  This function raises the system's current task priority level to the task 
  priority level of the mutual exclusion lock.  Then, it places the lock in the 
  acquired state.
  If Lock is NULL, then ASSERT().
  If Lock is not initialized, then ASSERT().
  If Lock is already in the acquired state, then ASSERT().

  @param  Lock              A pointer to the lock to acquire.

**/
VOID
EFIAPI
EfiAcquireLock (
  IN EFI_LOCK  *Lock
  )
{
  ASSERT (Lock != NULL);
  ASSERT (Lock->Lock == EfiLockReleased);

  Lock->OwnerTpl = gBS->RaiseTPL (Lock->Tpl);
  Lock->Lock     = EfiLockAcquired;
}

/**
  Acquires ownership of a lock.

  This function raises the system's current task priority level to the task priority
  level of the mutual exclusion lock.  Then, it attempts to place the lock in the acquired state.
  If the lock is already in the acquired state, then EFI_ACCESS_DENIED is returned.
  Otherwise, EFI_SUCCESS is returned.
  If Lock is NULL, then ASSERT().
  If Lock is not initialized, then ASSERT().

  @param  Lock              A pointer to the lock to acquire.

  @retval EFI_SUCCESS       The lock was acquired.
  @retval EFI_ACCESS_DENIED The lock could not be acquired because it is already owned.

**/
EFI_STATUS
EFIAPI
EfiAcquireLockOrFail (
  IN EFI_LOCK  *Lock
  )
{

  ASSERT (Lock != NULL);
  ASSERT (Lock->Lock != EfiLockUninitialized);

  if (Lock->Lock == EfiLockAcquired) {
    //
    // Lock is already owned, so bail out
    //
    return EFI_ACCESS_DENIED;
  }

  Lock->OwnerTpl = gBS->RaiseTPL (Lock->Tpl);

  Lock->Lock = EfiLockAcquired;

  return EFI_SUCCESS;
}

/**
  Releases ownership of a lock.

  This function transitions a mutual exclusion lock from the acquired state to 
  the released state, and restores the system's task priority level to its 
  previous level.
  If Lock is NULL, then ASSERT().
  If Lock is not initialized, then ASSERT().
  If Lock is already in the released state, then ASSERT().

  @param  Lock  A pointer to the lock to release.

**/
VOID
EFIAPI
EfiReleaseLock (
  IN EFI_LOCK  *Lock
  )
{
  EFI_TPL Tpl;

  ASSERT (Lock != NULL);
  ASSERT (Lock->Lock == EfiLockAcquired);

  Tpl = Lock->OwnerTpl;

  Lock->Lock = EfiLockReleased;

  gBS->RestoreTPL (Tpl);
}

/**
  Tests whether a controller handle is being managed by a specific driver.

  This function tests whether the driver specified by DriverBindingHandle is
  currently managing the controller specified by ControllerHandle.  This test
  is performed by evaluating if the the protocol specified by ProtocolGuid is
  present on ControllerHandle and is was opened by DriverBindingHandle with an
  attribute of EFI_OPEN_PROTOCOL_BY_DRIVER. 
  If ProtocolGuid is NULL, then ASSERT().

  @param  ControllerHandle     A handle for a controller to test.
  @param  DriverBindingHandle  Specifies the driver binding handle for the
                               driver.
  @param  ProtocolGuid         Specifies the protocol that the driver specified
                               by DriverBindingHandle opens in its Start()
                               function.

  @retval EFI_SUCCESS          ControllerHandle is managed by the driver
                               specified by DriverBindingHandle.
  @retval EFI_UNSUPPORTED      ControllerHandle is not managed by the driver
                               specified by DriverBindingHandle.

**/
EFI_STATUS
EFIAPI
EfiTestManagedDevice (
  IN CONST EFI_HANDLE       ControllerHandle,
  IN CONST EFI_HANDLE       DriverBindingHandle,
  IN CONST EFI_GUID         *ProtocolGuid
  )
{
  EFI_STATUS     Status;
  VOID           *ManagedInterface;

  ASSERT (ProtocolGuid != NULL);

  Status = gBS->OpenProtocol (
                  ControllerHandle,
                  (EFI_GUID *) ProtocolGuid,
                  &ManagedInterface,
                  DriverBindingHandle,
                  ControllerHandle,
                  EFI_OPEN_PROTOCOL_BY_DRIVER
                  );
  if (!EFI_ERROR (Status)) {
    gBS->CloseProtocol (
           ControllerHandle,
           (EFI_GUID *) ProtocolGuid,
           DriverBindingHandle,
           ControllerHandle
           );
    return EFI_UNSUPPORTED;
  }

  if (Status != EFI_ALREADY_STARTED) {
    return EFI_UNSUPPORTED;
  }

  return EFI_SUCCESS;
}

/**
  Tests whether a child handle is a child device of the controller.

  This function tests whether ChildHandle is one of the children of
  ControllerHandle.  This test is performed by checking to see if the protocol
  specified by ProtocolGuid is present on ControllerHandle and opened by
  ChildHandle with an attribute of EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER.
  If ProtocolGuid is NULL, then ASSERT().

  @param  ControllerHandle     A handle for a (parent) controller to test. 
  @param  ChildHandle          A child handle to test.
  @param  ProtocolGuid         Supplies the protocol that the child controller
                               opens on its parent controller. 

  @retval EFI_SUCCESS          ChildHandle is a child of the ControllerHandle.
  @retval EFI_UNSUPPORTED      ChildHandle is not a child of the
                               ControllerHandle.

**/
EFI_STATUS
EFIAPI
EfiTestChildHandle (
  IN CONST EFI_HANDLE       ControllerHandle,
  IN CONST EFI_HANDLE       ChildHandle,
  IN CONST EFI_GUID         *ProtocolGuid
  )
{
  EFI_STATUS                            Status;
  EFI_OPEN_PROTOCOL_INFORMATION_ENTRY   *OpenInfoBuffer;
  UINTN                                 EntryCount;
  UINTN                                 Index;

  ASSERT (ProtocolGuid != NULL);

  //
  // Retrieve the list of agents that are consuming the specific protocol
  // on ControllerHandle.
  //
  Status = gBS->OpenProtocolInformation (
                  ControllerHandle,
                  (EFI_GUID *) ProtocolGuid,
                  &OpenInfoBuffer,
                  &EntryCount
                  );
  if (EFI_ERROR (Status)) {
    return EFI_UNSUPPORTED;
  }

  //
  // Inspect if ChildHandle is one of the agents.
  //
  Status = EFI_UNSUPPORTED;
  for (Index = 0; Index < EntryCount; Index++) {
    if ((OpenInfoBuffer[Index].ControllerHandle == ChildHandle) &&
        (OpenInfoBuffer[Index].Attributes & EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER) != 0) {
      Status = EFI_SUCCESS;
      break;
    }
  }

  FreePool (OpenInfoBuffer);
  return Status;
}

/**
  This function looks up a Unicode string in UnicodeStringTable.

  If Language is a member of SupportedLanguages and a Unicode string is found in
  UnicodeStringTable that matches the language code specified by Language, then it
  is returned in UnicodeString.

  @param  Language                A pointer to the ISO 639-2 language code for the 
                                  Unicode string to look up and return.
  @param  SupportedLanguages      A pointer to the set of ISO 639-2 language codes 
                                  that the Unicode string table supports.  Language 
                                  must be a member of this set.
  @param  UnicodeStringTable      A pointer to the table of Unicode strings.
  @param  UnicodeString           A pointer to the Unicode string from UnicodeStringTable
                                  that matches the language specified by Language.

  @retval EFI_SUCCESS             The Unicode string that matches the language 
                                  specified by Language was found
                                  in the table of Unicode strings UnicodeStringTable, 
                                  and it was returned in UnicodeString.
  @retval EFI_INVALID_PARAMETER   Language is NULL.
  @retval EFI_INVALID_PARAMETER   UnicodeString is NULL.
  @retval EFI_UNSUPPORTED         SupportedLanguages is NULL.
  @retval EFI_UNSUPPORTED         UnicodeStringTable is NULL.
  @retval EFI_UNSUPPORTED         The language specified by Language is not a 
                                  member of SupportedLanguages.
  @retval EFI_UNSUPPORTED         The language specified by Language is not 
                                  supported by UnicodeStringTable.

**/
EFI_STATUS
EFIAPI
LookupUnicodeString (
  IN CONST CHAR8                     *Language,
  IN CONST CHAR8                     *SupportedLanguages,
  IN CONST EFI_UNICODE_STRING_TABLE  *UnicodeStringTable,
  OUT CHAR16                         **UnicodeString
  )
{
  //
  // Make sure the parameters are valid
  //
  if (Language == NULL || UnicodeString == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // If there are no supported languages, or the Unicode String Table is empty, then the
  // Unicode String specified by Language is not supported by this Unicode String Table
  //
  if (SupportedLanguages == NULL || UnicodeStringTable == NULL) {
    return EFI_UNSUPPORTED;
  }

  //
  // Make sure Language is in the set of Supported Languages
  //
  while (*SupportedLanguages != 0) {
    if (CompareIso639LanguageCode (Language, SupportedLanguages)) {

      //
      // Search the Unicode String Table for the matching Language specifier
      //
      while (UnicodeStringTable->Language != NULL) {
        if (CompareIso639LanguageCode (Language, UnicodeStringTable->Language)) {

          //
          // A matching string was found, so return it
          //
          *UnicodeString = UnicodeStringTable->UnicodeString;
          return EFI_SUCCESS;
        }

        UnicodeStringTable++;
      }

      return EFI_UNSUPPORTED;
    }

    SupportedLanguages += 3;
  }

  return EFI_UNSUPPORTED;
}



/**
  This function looks up a Unicode string in UnicodeStringTable.

  If Language is a member of SupportedLanguages and a Unicode string is found in
  UnicodeStringTable that matches the language code specified by Language, then
  it is returned in UnicodeString.

  @param  Language             A pointer to an ASCII string containing the ISO 639-2 or the
                               RFC 4646 language code for the Unicode string to look up and
                               return. If Iso639Language is TRUE, then this ASCII string is
                               not assumed to be Null-terminated, and only the first three
                               characters are used. If Iso639Language is FALSE, then this ASCII
                               string must be Null-terminated. 
  @param  SupportedLanguages   A pointer to a Null-terminated ASCII string that contains a
                               set of ISO 639-2 or RFC 4646 language codes that the Unicode
                               string table supports.  Language must be a member of this set.
                               If Iso639Language is TRUE, then this string contains one or more
                               ISO 639-2 language codes with no separator characters. If Iso639Language
                               is FALSE, then is string contains one or more RFC 4646 language
                               codes separated by ';'.
  @param  UnicodeStringTable   A pointer to the table of Unicode strings. Type EFI_UNICODE_STRING_TABLE
                               is defined in "Related Definitions".
  @param  UnicodeString        A pointer to the Null-terminated Unicode string from UnicodeStringTable
                               that matches the language specified by Language.
  @param  Iso639Language       Specifies the supported language code format. If it is TRUE, then
                               Language and SupportedLanguages follow ISO 639-2 language code format.
                               Otherwise, they follow RFC 4646 language code format.


  @retval  EFI_SUCCESS            The Unicode string that matches the language specified by Language
                                  was found in the table of Unicode strings UnicodeStringTable, and
                                  it was returned in UnicodeString.
  @retval  EFI_INVALID_PARAMETER  Language is NULL.  
  @retval  EFI_INVALID_PARAMETER  UnicodeString is NULL.  
  @retval  EFI_UNSUPPORTED        SupportedLanguages is NULL.  
  @retval  EFI_UNSUPPORTED        UnicodeStringTable is NULL.  
  @retval  EFI_UNSUPPORTED        The language specified by Language is not a member of SupportedLanguages.  
  @retval  EFI_UNSUPPORTED        The language specified by Language is not supported by UnicodeStringTable.

**/
EFI_STATUS
EFIAPI
LookupUnicodeString2 (
  IN CONST CHAR8                     *Language,
  IN CONST CHAR8                     *SupportedLanguages,
  IN CONST EFI_UNICODE_STRING_TABLE  *UnicodeStringTable,
  OUT CHAR16                         **UnicodeString,
  IN BOOLEAN                         Iso639Language
  )
{
  BOOLEAN   Found;
  UINTN     Index;
  CHAR8     *LanguageString;

  //
  // Make sure the parameters are valid
  //
  if (Language == NULL || UnicodeString == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // If there are no supported languages, or the Unicode String Table is empty, then the
  // Unicode String specified by Language is not supported by this Unicode String Table
  //
  if (SupportedLanguages == NULL || UnicodeStringTable == NULL) {
    return EFI_UNSUPPORTED;
  }

  //
  // Make sure Language is in the set of Supported Languages
  //
  Found = FALSE;
  while (*SupportedLanguages != 0) {
    if (Iso639Language) {
      if (CompareIso639LanguageCode (Language, SupportedLanguages)) {
        Found = TRUE;
        break;
      }
      SupportedLanguages += 3;
    } else {
      for (Index = 0; SupportedLanguages[Index] != 0 && SupportedLanguages[Index] != ';'; Index++);
      if ((AsciiStrnCmp(SupportedLanguages, Language, Index) == 0) && (Language[Index] == 0)) {
        Found = TRUE;
        break;
      }
      SupportedLanguages += Index;
      for (; *SupportedLanguages != 0 && *SupportedLanguages == ';'; SupportedLanguages++);
    }
  }

  //
  // If Language is not a member of SupportedLanguages, then return EFI_UNSUPPORTED
  //
  if (!Found) {
    return EFI_UNSUPPORTED;
  }

  //
  // Search the Unicode String Table for the matching Language specifier
  //
  while (UnicodeStringTable->Language != NULL) {
    LanguageString = UnicodeStringTable->Language;
    while (0 != *LanguageString) {
      for (Index = 0 ;LanguageString[Index] != 0 && LanguageString[Index] != ';'; Index++);
      if (AsciiStrnCmp(LanguageString, Language, Index) == 0) {
        *UnicodeString = UnicodeStringTable->UnicodeString;
        return EFI_SUCCESS;
      }
      LanguageString += Index;
      for (Index = 0 ;LanguageString[Index] != 0 && LanguageString[Index] == ';'; Index++);
    }
    UnicodeStringTable++;
  }

  return EFI_UNSUPPORTED;
}


/**
  This function adds a Unicode string to UnicodeStringTable.

  If Language is a member of SupportedLanguages then UnicodeString is added to 
  UnicodeStringTable.  New buffers are allocated for both Language and 
  UnicodeString.  The contents of Language and UnicodeString are copied into 
  these new buffers.  These buffers are automatically freed when 
  FreeUnicodeStringTable() is called.

  @param  Language                A pointer to the ISO 639-2 language code for the Unicode 
                                  string to add.
  @param  SupportedLanguages      A pointer to the set of ISO 639-2 language codes
                                  that the Unicode string table supports.
                                  Language must be a member of this set.
  @param  UnicodeStringTable      A pointer to the table of Unicode strings.
  @param  UnicodeString           A pointer to the Unicode string to add.

  @retval EFI_SUCCESS             The Unicode string that matches the language 
                                  specified by Language was found in the table of 
                                  Unicode strings UnicodeStringTable, and it was 
                                  returned in UnicodeString.
  @retval EFI_INVALID_PARAMETER   Language is NULL.
  @retval EFI_INVALID_PARAMETER   UnicodeString is NULL.
  @retval EFI_INVALID_PARAMETER   UnicodeString is an empty string.
  @retval EFI_UNSUPPORTED         SupportedLanguages is NULL.
  @retval EFI_ALREADY_STARTED     A Unicode string with language Language is 
                                  already present in UnicodeStringTable.
  @retval EFI_OUT_OF_RESOURCES    There is not enough memory to add another 
                                  Unicode string to UnicodeStringTable.
  @retval EFI_UNSUPPORTED         The language specified by Language is not a 
                                  member of SupportedLanguages.

**/
EFI_STATUS
EFIAPI
AddUnicodeString (
  IN CONST CHAR8               *Language,
  IN CONST CHAR8               *SupportedLanguages,
  IN EFI_UNICODE_STRING_TABLE  **UnicodeStringTable,
  IN CONST CHAR16              *UnicodeString
  )
{
  UINTN                     NumberOfEntries;
  EFI_UNICODE_STRING_TABLE  *OldUnicodeStringTable;
  EFI_UNICODE_STRING_TABLE  *NewUnicodeStringTable;
  UINTN                     UnicodeStringLength;

  //
  // Make sure the parameter are valid
  //
  if (Language == NULL || UnicodeString == NULL || UnicodeStringTable == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // If there are no supported languages, then a Unicode String can not be added
  //
  if (SupportedLanguages == NULL) {
    return EFI_UNSUPPORTED;
  }

  //
  // If the Unicode String is empty, then a Unicode String can not be added
  //
  if (UnicodeString[0] == 0) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // Make sure Language is a member of SupportedLanguages
  //
  while (*SupportedLanguages != 0) {
    if (CompareIso639LanguageCode (Language, SupportedLanguages)) {

      //
      // Determine the size of the Unicode String Table by looking for a NULL Language entry
      //
      NumberOfEntries = 0;
      if (*UnicodeStringTable != NULL) {
        OldUnicodeStringTable = *UnicodeStringTable;
        while (OldUnicodeStringTable->Language != NULL) {
          if (CompareIso639LanguageCode (Language, OldUnicodeStringTable->Language)) {
            return EFI_ALREADY_STARTED;
          }

          OldUnicodeStringTable++;
          NumberOfEntries++;
        }
      }

      //
      // Allocate space for a new Unicode String Table.  It must hold the current number of
      // entries, plus 1 entry for the new Unicode String, plus 1 entry for the end of table
      // marker
      //
      NewUnicodeStringTable = AllocatePool ((NumberOfEntries + 2) * sizeof (EFI_UNICODE_STRING_TABLE));
      if (NewUnicodeStringTable == NULL) {
        return EFI_OUT_OF_RESOURCES;
      }

      //
      // If the current Unicode String Table contains any entries, then copy them to the
      // newly allocated Unicode String Table.
      //
      if (*UnicodeStringTable != NULL) {
        CopyMem (
           NewUnicodeStringTable,
           *UnicodeStringTable,
           NumberOfEntries * sizeof (EFI_UNICODE_STRING_TABLE)
           );
      }

      //
      // Allocate space for a copy of the Language specifier
      //
      NewUnicodeStringTable[NumberOfEntries].Language = AllocateCopyPool (3, Language);
      if (NewUnicodeStringTable[NumberOfEntries].Language == NULL) {
        FreePool (NewUnicodeStringTable);
        return EFI_OUT_OF_RESOURCES;
      }

      //
      // Compute the length of the Unicode String
      //
      for (UnicodeStringLength = 0; UnicodeString[UnicodeStringLength] != 0; UnicodeStringLength++)
        ;

      //
      // Allocate space for a copy of the Unicode String
      //
      NewUnicodeStringTable[NumberOfEntries].UnicodeString = AllocateCopyPool (
                                                              (UnicodeStringLength + 1) * sizeof (CHAR16),
                                                              UnicodeString
                                                              );
      if (NewUnicodeStringTable[NumberOfEntries].UnicodeString == NULL) {
        FreePool (NewUnicodeStringTable[NumberOfEntries].Language);
        FreePool (NewUnicodeStringTable);
        return EFI_OUT_OF_RESOURCES;
      }

      //
      // Mark the end of the Unicode String Table
      //
      NewUnicodeStringTable[NumberOfEntries + 1].Language       = NULL;
      NewUnicodeStringTable[NumberOfEntries + 1].UnicodeString  = NULL;

      //
      // Free the old Unicode String Table
      //
      if (*UnicodeStringTable != NULL) {
        FreePool (*UnicodeStringTable);
      }

      //
      // Point UnicodeStringTable at the newly allocated Unicode String Table
      //
      *UnicodeStringTable = NewUnicodeStringTable;

      return EFI_SUCCESS;
    }

    SupportedLanguages += 3;
  }

  return EFI_UNSUPPORTED;
}


/**
  This function adds the Null-terminated Unicode string specified by UnicodeString
  to UnicodeStringTable.

  If Language is a member of SupportedLanguages then UnicodeString is added to
  UnicodeStringTable.  New buffers are allocated for both Language and UnicodeString.
  The contents of Language and UnicodeString are copied into these new buffers.
  These buffers are automatically freed when EfiLibFreeUnicodeStringTable() is called.

  @param  Language            A pointer to an ASCII string containing the ISO 639-2 or
                              the RFC 4646 language code for the Unicode string to add.
                              If Iso639Language is TRUE, then this ASCII string is not
                              assumed to be Null-terminated, and only the first three
                              chacters are used. If Iso639Language is FALSE, then this
                              ASCII string must be Null-terminated.
  @param  SupportedLanguages  A pointer to a Null-terminated ASCII string that contains
                              a set of ISO 639-2 or RFC 4646 language codes that the Unicode
                              string table supports.  Language must be a member of this set.
                              If Iso639Language is TRUE, then this string contains one or more
                              ISO 639-2 language codes with no separator characters.
                              If Iso639Language is FALSE, then is string contains one or more
                              RFC 4646 language codes separated by ';'.
  @param  UnicodeStringTable  A pointer to the table of Unicode strings. Type EFI_UNICODE_STRING_TABLE
                              is defined in "Related Definitions".
  @param  UnicodeString       A pointer to the Unicode string to add.  
  @param  Iso639Language      Specifies the supported language code format. If it is TRUE,
                              then Language and SupportedLanguages follow ISO 639-2 language code format.
                              Otherwise, they follow RFC 4646 language code format.

  @retval EFI_SUCCESS            The Unicode string that matches the language specified by
                                 Language was found in the table of Unicode strings UnicodeStringTable,
                                 and it was returned in UnicodeString.  
  @retval EFI_INVALID_PARAMETER  Language is NULL.  
  @retval EFI_INVALID_PARAMETER  UnicodeString is NULL.  
  @retval EFI_INVALID_PARAMETER  UnicodeString is an empty string.  
  @retval EFI_UNSUPPORTED        SupportedLanguages is NULL.  
  @retval EFI_ALREADY_STARTED    A Unicode string with language Language is already present in
                                 UnicodeStringTable.  
  @retval EFI_OUT_OF_RESOURCES   There is not enough memory to add another Unicode string UnicodeStringTable.  
  @retval EFI_UNSUPPORTED        The language specified by Language is not a member of SupportedLanguages.

**/
EFI_STATUS
EFIAPI
AddUnicodeString2 (
  IN CONST CHAR8               *Language,
  IN CONST CHAR8               *SupportedLanguages,
  IN EFI_UNICODE_STRING_TABLE  **UnicodeStringTable,
  IN CONST CHAR16              *UnicodeString,
  IN BOOLEAN                   Iso639Language
  )
{
  UINTN                     NumberOfEntries;
  EFI_UNICODE_STRING_TABLE  *OldUnicodeStringTable;
  EFI_UNICODE_STRING_TABLE  *NewUnicodeStringTable;
  UINTN                     UnicodeStringLength;
  BOOLEAN                   Found;
  UINTN                     Index;
  CHAR8                     *LanguageString;

  //
  // Make sure the parameter are valid
  //
  if (Language == NULL || UnicodeString == NULL || UnicodeStringTable == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // If there are no supported languages, then a Unicode String can not be added
  //
  if (SupportedLanguages == NULL) {
    return EFI_UNSUPPORTED;
  }

  //
  // If the Unicode String is empty, then a Unicode String can not be added
  //
  if (UnicodeString[0] == 0) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // Make sure Language is a member of SupportedLanguages
  //
  Found = FALSE;
  while (*SupportedLanguages != 0) {
    if (Iso639Language) {
      if (CompareIso639LanguageCode (Language, SupportedLanguages)) {
        Found = TRUE;
        break;
      }
      SupportedLanguages += 3;
    } else {
      for (Index = 0; SupportedLanguages[Index] != 0 && SupportedLanguages[Index] != ';'; Index++);
      if (AsciiStrnCmp(SupportedLanguages, Language, Index) == 0) {
        Found = TRUE;
        break;
      }
      SupportedLanguages += Index;
      for (; *SupportedLanguages != 0 && *SupportedLanguages == ';'; SupportedLanguages++);
    }
  }

  //
  // If Language is not a member of SupportedLanguages, then return EFI_UNSUPPORTED
  //
  if (!Found) {
    return EFI_UNSUPPORTED;
  }

  //
  // Determine the size of the Unicode String Table by looking for a NULL Language entry
  //
  NumberOfEntries = 0;
  if (*UnicodeStringTable != NULL) {
    OldUnicodeStringTable = *UnicodeStringTable;
    while (OldUnicodeStringTable->Language != NULL) {
      LanguageString = OldUnicodeStringTable->Language;

      while (*LanguageString != 0) {
        for (Index = 0; LanguageString[Index] != 0 && LanguageString[Index] != ';'; Index++);

        if (AsciiStrnCmp (Language, LanguageString, Index) == 0) { 
          return EFI_ALREADY_STARTED;
        }
        LanguageString += Index;
        for (; *LanguageString != 0 && *LanguageString == ';'; LanguageString++);
      }
      OldUnicodeStringTable++;
      NumberOfEntries++;
    }
  }

  //
  // Allocate space for a new Unicode String Table.  It must hold the current number of
  // entries, plus 1 entry for the new Unicode String, plus 1 entry for the end of table
  // marker
  //
  NewUnicodeStringTable = AllocatePool ((NumberOfEntries + 2) * sizeof (EFI_UNICODE_STRING_TABLE));
  if (NewUnicodeStringTable == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }

  //
  // If the current Unicode String Table contains any entries, then copy them to the
  // newly allocated Unicode String Table.
  //
  if (*UnicodeStringTable != NULL) {
    CopyMem (
      NewUnicodeStringTable,
      *UnicodeStringTable,
      NumberOfEntries * sizeof (EFI_UNICODE_STRING_TABLE)
      );
  }

  //
  // Allocate space for a copy of the Language specifier
  //
  NewUnicodeStringTable[NumberOfEntries].Language = AllocateCopyPool (AsciiStrSize(Language), Language);
  if (NewUnicodeStringTable[NumberOfEntries].Language == NULL) {
    FreePool (NewUnicodeStringTable);
    return EFI_OUT_OF_RESOURCES;
  }

  //
  // Compute the length of the Unicode String
  //
  for (UnicodeStringLength = 0; UnicodeString[UnicodeStringLength] != 0; UnicodeStringLength++);

  //
  // Allocate space for a copy of the Unicode String
  //
  NewUnicodeStringTable[NumberOfEntries].UnicodeString = AllocateCopyPool (StrSize (UnicodeString), UnicodeString);
  if (NewUnicodeStringTable[NumberOfEntries].UnicodeString == NULL) {
    FreePool (NewUnicodeStringTable[NumberOfEntries].Language);
    FreePool (NewUnicodeStringTable);
    return EFI_OUT_OF_RESOURCES;
  }

  //
  // Mark the end of the Unicode String Table
  //
  NewUnicodeStringTable[NumberOfEntries + 1].Language       = NULL;
  NewUnicodeStringTable[NumberOfEntries + 1].UnicodeString  = NULL;

  //
  // Free the old Unicode String Table
  //
  if (*UnicodeStringTable != NULL) {
    FreePool (*UnicodeStringTable);
  }

  //
  // Point UnicodeStringTable at the newly allocated Unicode String Table
  //
  *UnicodeStringTable = NewUnicodeStringTable;

  return EFI_SUCCESS;
}

/**
  This function frees the table of Unicode strings in UnicodeStringTable.

  If UnicodeStringTable is NULL, then EFI_SUCCESS is returned.
  Otherwise, each language code, and each Unicode string in the Unicode string 
  table are freed, and EFI_SUCCESS is returned.

  @param  UnicodeStringTable  A pointer to the table of Unicode strings.

  @retval EFI_SUCCESS         The Unicode string table was freed.

**/
EFI_STATUS
EFIAPI
FreeUnicodeStringTable (
  IN EFI_UNICODE_STRING_TABLE  *UnicodeStringTable
  )
{
  UINTN Index;

  //
  // If the Unicode String Table is NULL, then it is already freed
  //
  if (UnicodeStringTable == NULL) {
    return EFI_SUCCESS;
  }

  //
  // Loop through the Unicode String Table until we reach the end of table marker
  //
  for (Index = 0; UnicodeStringTable[Index].Language != NULL; Index++) {

    //
    // Free the Language string from the Unicode String Table
    //
    FreePool (UnicodeStringTable[Index].Language);

    //
    // Free the Unicode String from the Unicode String Table
    //
    if (UnicodeStringTable[Index].UnicodeString != NULL) {
      FreePool (UnicodeStringTable[Index].UnicodeString);
    }
  }

  //
  // Free the Unicode String Table itself
  //
  FreePool (UnicodeStringTable);

  return EFI_SUCCESS;
}

#ifndef DISABLE_NEW_DEPRECATED_INTERFACES

/**
  [ATTENTION] This function will be deprecated for security reason.

  Returns a pointer to an allocated buffer that contains the contents of a 
  variable retrieved through the UEFI Runtime Service GetVariable().  The 
  returned buffer is allocated using AllocatePool().  The caller is responsible
  for freeing this buffer with FreePool().

  If Name is NULL, then ASSERT().
  If Guid is NULL, then ASSERT().

  @param[in]  Name  The pointer to a Null-terminated Unicode string.
  @param[in]  Guid  The pointer to an EFI_GUID structure

  @retval NULL   The variable could not be retrieved.
  @retval NULL   There are not enough resources available for the variable contents.
  @retval Other  A pointer to allocated buffer containing the variable contents.

**/
VOID *
EFIAPI
GetVariable (
  IN CONST CHAR16    *Name,
  IN CONST EFI_GUID  *Guid
  )
{
  EFI_STATUS  Status;
  UINTN       Size;
  VOID        *Value;

  ASSERT (Name != NULL);
  ASSERT (Guid != NULL);

  //
  // Try to get the variable size.
  //
  Value = NULL;
  Size = 0;
  Status = gRT->GetVariable ((CHAR16 *) Name, (EFI_GUID *) Guid, NULL, &Size, Value);
  if (Status != EFI_BUFFER_TOO_SMALL) {
    return NULL;
  }

  //
  // Allocate buffer to get the variable.
  //
  Value = AllocatePool (Size);
  if (Value == NULL) {
    return NULL;
  }

  //
  // Get the variable data.
  //
  Status = gRT->GetVariable ((CHAR16 *) Name, (EFI_GUID *) Guid, NULL, &Size, Value);
  if (EFI_ERROR (Status)) {
    FreePool(Value);
    return NULL;
  }

  return Value;
}

/**
  [ATTENTION] This function will be deprecated for security reason.

  Returns a pointer to an allocated buffer that contains the contents of a 
  variable retrieved through the UEFI Runtime Service GetVariable().  This 
  function always uses the EFI_GLOBAL_VARIABLE GUID to retrieve variables.
  The returned buffer is allocated using AllocatePool().  The caller is 
  responsible for freeing this buffer with FreePool().

  If Name is NULL, then ASSERT().

  @param[in]  Name  The pointer to a Null-terminated Unicode string.

  @retval NULL   The variable could not be retrieved.
  @retval NULL   There are not enough resources available for the variable contents.
  @retval Other  A pointer to allocated buffer containing the variable contents.

**/
VOID *
EFIAPI
GetEfiGlobalVariable (
  IN CONST CHAR16  *Name
  )
{
  return GetVariable (Name, &gEfiGlobalVariableGuid);
}
#endif

/**
  Returns the status whether get the variable success. The function retrieves 
  variable  through the UEFI Runtime Service GetVariable().  The 
  returned buffer is allocated using AllocatePool().  The caller is responsible
  for freeing this buffer with FreePool().

  If Name  is NULL, then ASSERT().
  If Guid  is NULL, then ASSERT().
  If Value is NULL, then ASSERT().

  @param[in]  Name  The pointer to a Null-terminated Unicode string.
  @param[in]  Guid  The pointer to an EFI_GUID structure
  @param[out] Value The buffer point saved the variable info.
  @param[out] Size  The buffer size of the variable.

  @return EFI_OUT_OF_RESOURCES      Allocate buffer failed.
  @return EFI_SUCCESS               Find the specified variable.
  @return Others Errors             Return errors from call to gRT->GetVariable.

**/
EFI_STATUS
EFIAPI
GetVariable2 (
  IN CONST CHAR16    *Name,
  IN CONST EFI_GUID  *Guid,
  OUT VOID           **Value,
  OUT UINTN          *Size OPTIONAL
  )
{
  EFI_STATUS  Status;
  UINTN       BufferSize;

  ASSERT (Name != NULL && Guid != NULL && Value != NULL);

  //
  // Try to get the variable size.
  //
  BufferSize = 0;
  *Value     = NULL;
  if (Size != NULL) {
    *Size  = 0;
  }
  
  Status = gRT->GetVariable ((CHAR16 *) Name, (EFI_GUID *) Guid, NULL, &BufferSize, *Value);
  if (Status != EFI_BUFFER_TOO_SMALL) {
    return Status;
  }

  //
  // Allocate buffer to get the variable.
  //
  *Value = AllocatePool (BufferSize);
  ASSERT (*Value != NULL);
  if (*Value == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }

  //
  // Get the variable data.
  //
  Status = gRT->GetVariable ((CHAR16 *) Name, (EFI_GUID *) Guid, NULL, &BufferSize, *Value);
  if (EFI_ERROR (Status)) {
    FreePool(*Value);
    *Value = NULL;
  }

  if (Size != NULL) {
    *Size = BufferSize;
  }

  return Status;
}

/**
  Returns a pointer to an allocated buffer that contains the contents of a 
  variable retrieved through the UEFI Runtime Service GetVariable().  This 
  function always uses the EFI_GLOBAL_VARIABLE GUID to retrieve variables.
  The returned buffer is allocated using AllocatePool().  The caller is 
  responsible for freeing this buffer with FreePool().

  If Name is NULL, then ASSERT().
  If Value is NULL, then ASSERT().

  @param[in]  Name  The pointer to a Null-terminated Unicode string.
  @param[out] Value The buffer point saved the variable info.
  @param[out] Size  The buffer size of the variable.

  @return EFI_OUT_OF_RESOURCES      Allocate buffer failed.
  @return EFI_SUCCESS               Find the specified variable.
  @return Others Errors             Return errors from call to gRT->GetVariable.

**/
EFI_STATUS
EFIAPI
GetEfiGlobalVariable2 (
  IN CONST CHAR16    *Name,
  OUT VOID           **Value,
  OUT UINTN          *Size OPTIONAL
  )
{
  return GetVariable2 (Name, &gEfiGlobalVariableGuid, Value, Size);
}

/**
  Returns a pointer to an allocated buffer that contains the best matching language 
  from a set of supported languages.  
  
  This function supports both ISO 639-2 and RFC 4646 language codes, but language 
  code types may not be mixed in a single call to this function.  The language 
  code returned is allocated using AllocatePool().  The caller is responsible for 
  freeing the allocated buffer using FreePool().  This function supports a variable
  argument list that allows the caller to pass in a prioritized list of language 
  codes to test against all the language codes in SupportedLanguages. 

  If SupportedLanguages is NULL, then ASSERT().

  @param[in]  SupportedLanguages  A pointer to a Null-terminated ASCII string that
                                  contains a set of language codes in the format 
                                  specified by Iso639Language.
  @param[in]  Iso639Language      If TRUE, then all language codes are assumed to be
                                  in ISO 639-2 format.  If FALSE, then all language
                                  codes are assumed to be in RFC 4646 language format
  @param[in]  ...                 A variable argument list that contains pointers to 
                                  Null-terminated ASCII strings that contain one or more
                                  language codes in the format specified by Iso639Language.
                                  The first language code from each of these language
                                  code lists is used to determine if it is an exact or
                                  close match to any of the language codes in 
                                  SupportedLanguages.  Close matches only apply to RFC 4646
                                  language codes, and the matching algorithm from RFC 4647
                                  is used to determine if a close match is present.  If 
                                  an exact or close match is found, then the matching
                                  language code from SupportedLanguages is returned.  If
                                  no matches are found, then the next variable argument
                                  parameter is evaluated.  The variable argument list 
                                  is terminated by a NULL.

  @retval NULL   The best matching language could not be found in SupportedLanguages.
  @retval NULL   There are not enough resources available to return the best matching 
                 language.
  @retval Other  A pointer to a Null-terminated ASCII string that is the best matching 
                 language in SupportedLanguages.

**/
CHAR8 *
EFIAPI
GetBestLanguage (
  IN CONST CHAR8  *SupportedLanguages, 
  IN BOOLEAN      Iso639Language,
  ...
  )
{
  VA_LIST      Args;
  CHAR8        *Language;
  UINTN        CompareLength;
  UINTN        LanguageLength;
  CONST CHAR8  *Supported;
  CHAR8        *BestLanguage;

  ASSERT (SupportedLanguages != NULL);

  VA_START (Args, Iso639Language);
  while ((Language = VA_ARG (Args, CHAR8 *)) != NULL) {
    //
    // Default to ISO 639-2 mode
    //
    CompareLength  = 3;
    LanguageLength = MIN (3, AsciiStrLen (Language));

    //
    // If in RFC 4646 mode, then determine the length of the first RFC 4646 language code in Language
    //
    if (!Iso639Language) {
      for (LanguageLength = 0; Language[LanguageLength] != 0 && Language[LanguageLength] != ';'; LanguageLength++);
    }

    //
    // Trim back the length of Language used until it is empty
    //
    while (LanguageLength > 0) {
      //
      // Loop through all language codes in SupportedLanguages
      //
      for (Supported = SupportedLanguages; *Supported != '\0'; Supported += CompareLength) {
        //
        // In RFC 4646 mode, then Loop through all language codes in SupportedLanguages
        //
        if (!Iso639Language) {
          //
          // Skip ';' characters in Supported
          //
          for (; *Supported != '\0' && *Supported == ';'; Supported++);
          //
          // Determine the length of the next language code in Supported
          //
          for (CompareLength = 0; Supported[CompareLength] != 0 && Supported[CompareLength] != ';'; CompareLength++);
          //
          // If Language is longer than the Supported, then skip to the next language
          //
          if (LanguageLength > CompareLength) {
            continue;
          }
        }
        //
        // See if the first LanguageLength characters in Supported match Language
        //
        if (AsciiStrnCmp (Supported, Language, LanguageLength) == 0) {
          VA_END (Args);
          //
          // Allocate, copy, and return the best matching language code from SupportedLanguages
          //
          BestLanguage = AllocateZeroPool (CompareLength + 1);
          if (BestLanguage == NULL) {
            return NULL;
          }
          return CopyMem (BestLanguage, Supported, CompareLength);
        }
      }

      if (Iso639Language) {
        //
        // If ISO 639 mode, then each language can only be tested once
        //
        LanguageLength = 0;
      } else {
        //
        // If RFC 4646 mode, then trim Language from the right to the next '-' character 
        //
        for (LanguageLength--; LanguageLength > 0 && Language[LanguageLength] != '-'; LanguageLength--);
      }
    }
  }
  VA_END (Args);

  //
  // No matches were found 
  //
  return NULL;
}