[reactos] 12/72: [NTFS] Simplify and optimize InternalSetResidentAttributeLength(), as suggested by Pierre.

[Trevor Thompson]

https://git.reactos.org/?p=reactos.git;a=commitdiff;h=c08d37d182408f69533644...

commit c08d37d182408f69533644257ee8cc10e6a16f6b
Author: Trevor Thompson [e-mail]
AuthorDate: Thu Jul 7 08:17:07 2016 +0000

[NTFS]
    Simplify and optimize InternalSetResidentAttributeLength(), as suggested by Pierre.

svn path=/branches/GSoC_2016/NTFS/; revision=71837
---
 drivers/filesystems/ntfs/mft.c | 34 ++++++++++++++--------------------
 1 file changed, 14 insertions(+), 20 deletions(-)

diff --git a/drivers/filesystems/ntfs/mft.c b/drivers/filesystems/ntfs/mft.c
index a5111c18ee..aa203bbe9d 100644
--- a/drivers/filesystems/ntfs/mft.c
+++ b/drivers/filesystems/ntfs/mft.c
@@ -178,43 +178,37 @@ InternalSetResidentAttributeLength(PNTFS_ATTR_CONTEXT AttrContext,
                                    ULONG AttrOffset,
                                    ULONG DataSize)
 {
-    ULONG EndMarker = AttributeEnd;
-    ULONG FinalMarker = FILE_RECORD_END;
+    PNTFS_ATTR_RECORD Destination = (PNTFS_ATTR_RECORD)((ULONG_PTR)FileRecord + AttrOffset);
     ULONG NextAttributeOffset;
-    ULONG Offset;
-    USHORT Padding;

DPRINT("InternalSetResidentAttributeLength( %p, %p, %lu, %lu )\n", AttrContext, FileRecord, AttrOffset, DataSize);

// update ValueLength Field
-    AttrContext->Record.Resident.ValueLength = DataSize;
-    Offset = AttrOffset + FIELD_OFFSET(NTFS_ATTR_RECORD, Resident.ValueLength);
-    RtlCopyMemory((PCHAR)FileRecord + Offset, &DataSize, sizeof(ULONG));
+    AttrContext->Record.Resident.ValueLength =
+    Destination->Resident.ValueLength = DataSize;

// calculate the record length and end marker offset
-    AttrContext->Record.Length = DataSize + AttrContext->Record.Resident.ValueOffset;
+    AttrContext->Record.Length =
+    Destination->Length = DataSize + AttrContext->Record.Resident.ValueOffset;
     NextAttributeOffset = AttrOffset + AttrContext->Record.Length;

// Ensure NextAttributeOffset is aligned to an 8-byte boundary
     if (NextAttributeOffset % 8 != 0)
     {
-        Padding = 8 - (NextAttributeOffset % 8);
+        USHORT Padding = 8 - (NextAttributeOffset % 8);
         NextAttributeOffset += Padding;
         AttrContext->Record.Length += Padding;
+        Destination->Length += Padding;
     }
+    
+    // advance Destination to the final "attribute" and write the end type
+    (ULONG_PTR)Destination += Destination->Length;
+    Destination->Type = AttributeEnd;

-    // update the record length
-    Offset = AttrOffset + FIELD_OFFSET(NTFS_ATTR_RECORD, Length);
-    RtlCopyMemory((PCHAR)FileRecord + Offset, &AttrContext->Record.Length, sizeof(ULONG));
+    // write the final marker (which shares the same offset and type as the Length field)
+    Destination->Length = FILE_RECORD_END;

-    // write the end marker 
-    RtlCopyMemory((PCHAR)FileRecord + NextAttributeOffset, &EndMarker, sizeof(ULONG));
-
-    // write the final marker
-    Offset = NextAttributeOffset + sizeof(ULONG);
-    RtlCopyMemory((PCHAR)FileRecord + Offset, &FinalMarker, sizeof(ULONG));
-
-    FileRecord->BytesInUse = Offset + sizeof(ULONG);
+    FileRecord->BytesInUse = NextAttributeOffset + (sizeof(ULONG) * 2);
 }

NTSTATUS