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UefiCpuPkg: 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: Jeff Fan <jeff.fan@intel.com>
This commit is contained in:
Hao Wu
2017-02-17 11:54:10 +08:00
parent 3ee1680978
commit 8491e302e1
5 changed files with 13 additions and 13 deletions
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4
UefiCpuPkg/CpuIo2Dxe/CpuIo2Dxe.c
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@ -1,7 +1,7 @@
/** @file
Produces the CPU I/O 2 Protocol.
Copyright (c) 2009 - 2012, Intel Corporation. All rights reserved.<BR>
Copyright (c) 2009 - 2017, Intel Corporation. All rights reserved.<BR>
Copyright (c) 2017, AMD Incorporated. All rights reserved.<BR>
This program and the accompanying materials
@ -141,7 +141,7 @@ CpuIoCheckParameter (
//
// Check to see if Address is aligned
//
if ((Address & (UINT64)(mInStride[Width] - 1)) != 0) {
if ((Address & ((UINT64)mInStride[Width] - 1)) != 0) {
return EFI_UNSUPPORTED;
}