From ReactOS

Windows XP version of LARGE_STRING

typedef struct _LARGE_UNICODE_STRING
{
  ULONG Length;           // 000
  ULONG MaximumLength:31; // 004
  ULONG bAnsi:1;          // 004
  PWSTR Buffer;           // 008
} LARGE_UNICODE_STRING *PLARGE_UNICODE_STRING;
//
//
typedef struct _LARGE_STRING
{
  ULONG Length;
  ULONG MaximumLength:31;
  ULONG bAnsi:1;
  PVOID Buffer;
} LARGE_STRING, *PLARGE_STRING;
//
// Based on ANSI_STRING
//
typedef struct _LARGE_ANSI_STRING
{
  ULONG Length;
  ULONG MaximumLength:31;
  ULONG bAnsi:1;
  PCHAR Buffer;
} LARGE_ANSI_STRING, *PLARGE_ANSI_STRING;

References

• Windows Symbol files, userkdx.dll, !dso