NetworkPkg: 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: Wu Jiaxin <jiaxin.wu@intel.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/NetworkPkg/UefiPxeBcDxe/PxeBcImpl.c b/NetworkPkg/UefiPxeBcDxe/PxeBcImpl.c
index e24c573e32..36477e9f80 100644
--- a/NetworkPkg/UefiPxeBcDxe/PxeBcImpl.c
+++ b/NetworkPkg/UefiPxeBcDxe/PxeBcImpl.c
@@ -1,7 +1,7 @@
 /** @file

   This implementation of EFI_PXE_BASE_CODE_PROTOCOL and EFI_LOAD_FILE_PROTOCOL.

 

-  Copyright (c) 2007 - 2016, Intel Corporation. All rights reserved.<BR>

+  Copyright (c) 2007 - 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

@@ -95,8 +95,8 @@ EfiPxeBcStart (
     //

     // Configure block size for TFTP as a default value to handle all link layers.

     //

-    Private->BlockSize = (UINTN) (Private->Ip6MaxPacketSize -

-                           PXEBC_DEFAULT_UDP_OVERHEAD_SIZE - PXEBC_DEFAULT_TFTP_OVERHEAD_SIZE);

+    Private->BlockSize = Private->Ip6MaxPacketSize -

+                           PXEBC_DEFAULT_UDP_OVERHEAD_SIZE - PXEBC_DEFAULT_TFTP_OVERHEAD_SIZE;

 

     //

     // PXE over IPv6 starts here, initialize the fields and list header.

@@ -148,8 +148,8 @@ EfiPxeBcStart (
     //

     // Configure block size for TFTP as a default value to handle all link layers.

     //

-    Private->BlockSize = (UINTN) (Private->Ip4MaxPacketSize -

-                           PXEBC_DEFAULT_UDP_OVERHEAD_SIZE - PXEBC_DEFAULT_TFTP_OVERHEAD_SIZE);

+    Private->BlockSize = Private->Ip4MaxPacketSize -

+                           PXEBC_DEFAULT_UDP_OVERHEAD_SIZE - PXEBC_DEFAULT_TFTP_OVERHEAD_SIZE;

 

     //

     // PXE over IPv4 starts here, initialize the fields.