On 10/08/12 10:05, Sergey Isakov wrote:
> Hi sirs,
> I encounter next problem.
> ----------
> c:\tiano\edk2\mdepkg\library\baselib\math64.c(89) : warning C6334:
> sizeof operator applied to an expression with an operator might yield
> unexpected results.
> ----------
> The code is the follow
> ------
> //
> // Test if this compiler supports arithmetic shift
> //
> TestValue = (((-1) << (sizeof (-1) * 8 - 1)) >> (sizeof (-1) * 8 - 1));
> if (TestValue == -1) {
> //
> // Arithmetic shift is supported
>
> ------
> It seems VS2012 don't like sizeof(-1).
> Switch off some warning?
>From search results for this warning message, VS2012 apparently warns
that the operand of the sizeof operator is not evaluated.
ISO C99 6.5.3.4 The sizeof operator
2 [...] If the type of the operand is a variable length array type,
the operand is evaluated; otherwise, the operand is not evaluated
[...]
However, VS2012 should rather warn about the sub-expression below,
because it invokes undefined behavior (C99 6.5.7p4):
(-1) << (sizeof (-1) * 8 - 1)
Laszlo
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