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NetworkPkg: Refine casting expression result to bigger size

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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>
This commit is contained in:
Hao Wu
2017-02-16 14:58:03 +08:00
parent bcee1b9f17
commit ce5c3273c3
5 changed files with 15 additions and 15 deletions
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10
NetworkPkg/UefiPxeBcDxe/PxeBcImpl.c
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@@ -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.