[PATCH v2 0/1] Refine casting expression result to bigger size

[Hao Wu <hao.a.wu@intel.com>]

Please note that this patch is maily for feedback collection and the patch
only covers MdePkg. We are working on patches for other packages.


V2:
Follow the below rules to refine codes:
1). When the expression will not overflow within the rank of "int", remove
the explicit type casts:
c = a + b;

2). When the expression is possible to overflow the range of unsigned int/
int:
c = (UINT64)a + b;

V1:
There are cases that the operands of an expression are all with rank less
than UINT64/INT64 and the result of the expression is casted 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.

For the consideration of generated binaries size, the commit will keep the
size of the operands as the size of int, and explitly add a type cast
before converting the result to UINT64/INT64.

1). When there is no operand with type UINTN
(UINTN)  (a + b) -> (UINTN)(UINT32)  (a + b) or
(UINT64) (a + b) -> (UINT64)(UINT32) (a + b)

2). Otherwise
(UINT64) (a + b) -> (UINT64)(UINTN)  (a + b)

Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>

Hao Wu (1):
  MdePkg: Refine casting expression result to bigger size

 MdePkg/Library/BaseLib/String.c                              |  4 ++--
 MdePkg/Library/BasePeCoffLib/BasePeCoff.c                    | 12 +++++-------
 MdePkg/Library/BaseS3PciLib/S3PciLib.c                       |  4 ++--
 MdePkg/Library/SmmMemoryAllocationLib/MemoryAllocationLib.c  |  4 ++--
 MdePkg/Library/UefiMemoryAllocationLib/MemoryAllocationLib.c |  4 ++--
 5 files changed, 13 insertions(+), 15 deletions(-)

-- 
1.9.5.msysgit.0