tech-userlevel archive

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Old Index]

Re: type behavior of sys/endian.h

On Jul 25, 2009, at 9:41 PM, David Holland wrote:

On Wed, Jul 22, 2009 at 01:12:42AM +0200, Joerg Sonnenberger wrote:
Or maybe they should be made inline functions instead so they don't
fail silently if passed pointers.

So we have two approach:
(1) Cast the value directly.
(2) Use inline functions.

When doing (2), fxp(4) doesn't compile as the follow construct triggers
a gcc warning:
with mask being some signed small constant. This even happens if mask is
unsigned or already of the correct width.

le16toh(~1)      -> nothing
le16toh(~1U) -> "large integer implicitly truncated to unsigned type"
le16toh(~32767)  -> nothing
le16toh(~32767U) -> "large integer implicitly truncated to unsigned type" le16toh(~32769) -> "large integer implicitly truncated to unsigned type" le16toh(~32769U) -> "large integer implicitly truncated to unsigned type"

This makes no sense, and I think gcc must be doing something wrong
internally, more than just printing a not-quite-relevant message. But
everything involving shorts is aggravating, so maybe not.

This make perfect sense to me.  The two values without a warning
convert from int to short with no loss of representation.  All the
other have value outside -32768..32767 and thus must be truncated to fit.

The warning happens when N != (short) N or N != (unsigned short) N
depending on whether N is unsigned.

Home | Main Index | Thread Index | Old Index