[BOOT:LIB] Implement EfiInitpConvertEfiFilePath()

Also implemented RtlULongSub() and EfiInitpAppendPathString()

SDK/INC/NT/ntrtl.h

@@ -18,6 +18,7 @@ Abstract:
 
 #include <string.h>
 #include <ntdef.h>
+#include <ntstatus.h>
 
 //
 // Memory operations.
@@ -27,6 +28,47 @@ Abstract:
 #define RtlFillMemory(Destination, Length, Fill)   memset((Destination), (Fill), (Length))
 #define RtlZeroMemory(Destination, Length)         memset((Destination), 0, (Length))
 
+#define ULONG_ERROR 0xFFFFFFFFUL
+
+FORCEINLINE
+NTSTATUS
+RtlULongSub (
+   IN ULONG ulMinuend,
+   IN ULONG ulSubtrahend,
+   IN OUT PULONG pulResult
+   )
+
+/*++
+
+Routine Description:
+
+    Calculates the difference of two ULONG values.
+
+Arguments:
+
+    ulMinuend - The value to subtract ulSubtrahend from.
+
+    ulSubtrahend - The value to subtract from ulMinuend.
+
+    pulResult - Pointer to a ULONG to store the difference in.
+
+Return Value:
+
+    STATUS_SUCCESS if successful.
+    STATUS_INTEGER_OVERFLOW if unsuccessful.
+
+--*/
+
+{
+    if (ulMinuend >= ulSubtrahend) {
+        *pulResult = ulMinuend - ulSubtrahend;
+        return STATUS_SUCCESS;
+    }
+
+    *pulResult = ULONG_ERROR;
+    return STATUS_INTEGER_OVERFLOW;
+}
+
 VOID
 NTAPI
 RtlInitUnicodeString (

SDK/INC/NT/ntstatus.h

@@ -29,6 +29,7 @@ Abstract:
 #define STATUS_DISK_CORRUPT_ERROR      ((NTSTATUS) 0xC0000032L)
 #define STATUS_DEVICE_ALREADY_ATTACHED ((NTSTATUS) 0xC0000038L)
 #define STATUS_DISK_FULL               ((NTSTATUS) 0xC000007FL)
+#define STATUS_INTEGER_OVERFLOW        ((NTSTATUS) 0xC0000095L)
 #define STATUS_INSUFFICIENT_RESOURCES  ((NTSTATUS) 0xC000009AL)
 #define STATUS_MEDIA_WRITE_PROTECTED   ((NTSTATUS) 0xC00000A2L)
 #define STATUS_DEVICE_NOT_READY        ((NTSTATUS) 0xC00000A3L)