FatPkg: Refine casting expression result to bigger size

There are cases that the operands of an expression are all with rank less
than UINT64/INT64 and the result of the expression is explicitly cast to
UINT64/INT64 to fit the target size.

An example will be:
UINT32 a,b;
// a and b can be any unsigned int type with rank less than UINT64, like
// UINT8, UINT16, etc.
UINT64 c;
c = (UINT64) (a + b);

Some static code checkers may warn that the expression result might
overflow within the rank of "int" (integer promotions) and the result is
then cast to a bigger size.

The commit refines codes by the following rules:
1). When the expression is possible to overflow the range of unsigned int/
int:
c = (UINT64)a + b;

2). When the expression will not overflow within the rank of "int", remove
the explicit type casts:
c = a + b;

3). When the expression will be cast to pointer of possible greater size:
UINT32 a,b;
VOID *c;
c = (VOID *)(UINTN)(a + b); --> c = (VOID *)((UINTN)a + b);

4). When one side of a comparison expression contains only operands with
rank less than UINT32:
UINT8 a;
UINT16 b;
UINTN c;
if ((UINTN)(a + b) > c) {...} --> if (((UINT32)a + b) > c) {...}

For rule 4), if we remove the 'UINTN' type cast like:
if (a + b > c) {...}
The VS compiler will complain with warning C4018 (signed/unsigned
mismatch, level 3 warning) due to promoting 'a + b' to type 'int'.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>

2 files changed, 4 insertions, 4 deletions

diff --git a/FatPkg/EnhancedFatDxe/ReadWrite.c b/FatPkg/EnhancedFatDxe/ReadWrite.c
index a6e0ec4c13..ad3c260412 100644
--- a/FatPkg/EnhancedFatDxe/ReadWrite.c
+++ b/FatPkg/EnhancedFatDxe/ReadWrite.c
@@ -1,7 +1,7 @@
 /** @file

   Functions that perform file read/write.

 

-Copyright (c) 2005 - 2015, Intel Corporation. All rights reserved.<BR>

+Copyright (c) 2005 - 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

@@ -173,7 +173,7 @@ Done:
     // Update IFile->Position, if everything is all right

     //

     CurrentPos      = ODir->CurrentPos;

-    IFile->Position = (UINT64) (CurrentPos * sizeof (FAT_DIRECTORY_ENTRY));

+    IFile->Position = CurrentPos * sizeof (FAT_DIRECTORY_ENTRY);

   }

 

   return Status;

diff --git a/FatPkg/FatPei/FatLiteAccess.c b/FatPkg/FatPei/FatLiteAccess.c
index 110634508b..a92c5bff99 100644
--- a/FatPkg/FatPei/FatLiteAccess.c
+++ b/FatPkg/FatPei/FatLiteAccess.c
@@ -1,7 +1,7 @@
 /** @file

   FAT file system access routines for FAT recovery PEIM

 

-Copyright (c) 2006 - 2013, Intel Corporation. All rights reserved.<BR>

+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

@@ -393,7 +393,7 @@ FatReadFile (
   } else {

 

     if ((File->Attributes & FAT_ATTR_DIRECTORY) == 0) {

-      Size = Size < (File->FileSize - File->CurrentPos) ? Size : (UINTN) (File->FileSize - File->CurrentPos);

+      Size = Size < (File->FileSize - File->CurrentPos) ? Size : (File->FileSize - File->CurrentPos);

     }

     //

     // This is a normal cluster based file