svn commit: r362781 - head/sys/compat/linuxkpi/common/include/linux

[Ian Lepore]

On Mon, 2020-06-29 at 14:26 -0600, Warner Losh wrote:
> On Mon, Jun 29, 2020, 2:15 PM Ravi Pokala <rpokala at freebsd.org>
> wrote:
> 
> > -----Original Message-----
> > From: <owner-src-committers at freebsd.org> on behalf of Hans Petter
> > Selasky
> > <hselasky at FreeBSD.org>
> > Date: 2020-06-29, Monday at 06:08
> > To: <src-committers at freebsd.org>, <svn-src-all at freebsd.org>, <
> > svn-src-head at freebsd.org>
> > Subject: svn commit: r362781 -
> > head/sys/compat/linuxkpi/common/include/linux
> > 
> >     Author: hselasky
> >     Date: Mon Jun 29 13:08:40 2020
> >     New Revision: 362781
> >     URL: https://svnweb.freebsd.org/changeset/base/362781
> > 
> >     Log:
> >       Implement is_signed(), type_max() and type_min() function
> > macros in
> > the
> >       LinuxKPI.
> > 
> >       MFC after:        1 week
> >       Sponsored by:     Mellanox Technologies
> > 
> >     Modified:
> >       head/sys/compat/linuxkpi/common/include/linux/kernel.h
> > 
> >     Modified:
> > head/sys/compat/linuxkpi/common/include/linux/kernel.h
> > 
> > ===================================================================
> > ===========
> >     --- head/sys/compat/linuxkpi/common/include/linux/kernel.h  Mon
> > Jun 29
> > 12:59:09 2020        (r362780)
> >     +++ head/sys/compat/linuxkpi/common/include/linux/kernel.h  Mon
> > Jun 29
> > 13:08:40 2020        (r362781)
> >     @@ -564,4 +564,20 @@ linux_ratelimited(linux_ratelimit_t *rl)
> >      #define    __is_constexpr(x) \
> >         __builtin_constant_p(x)
> > 
> > Hi Hans,
> > 
> >     +#define            is_signed(x) (((x)-1 / (x)2) == (x)0)
> > 
> > It took me several reads to understand this, until I figured out
> > that 'x'
> > is not a variable, it's the name of a *type*.
> > 
> > If 'x' is a variable, then '(x)-1' is subtraction, but '(x)2' and
> > '(x)0'
> > are nonsensical.
> > 
> > If 'x' is a *type*, then '(x)-1' is typecasting '-1', and similarly
> > for
> > '(x)2' and '(x)0'.
> > 
> > So, perhaps a comment, or a better name for 'x'?
> > 
> 
> I had similar thoughts. Maybe 't' instead?
> 

Or maybe since there's no one-character restriction on macro variable
names, something actually descriptive like 'datatype'.  

-- Ian

> Warner
> 
> Thanks,
> > 
> > Ravi (rpokala@)
> > 
> >     +#define            type_max(x) (
> >      \
> >     +  (sizeof(x) >= 8) ? (is_signed(x) ? INT64_MAX : UINT64_MAX)
> > :     \
> >     +  (sizeof(x) >= 4) ? (is_signed(x) ? INT32_MAX : UINT32_MAX)
> > :     \
> >     +  (sizeof(x) >= 2) ? (is_signed(x) ? INT16_MAX : UINT16_MAX)
> > :     \
> >     +                (is_signed(x) ? INT8_MAX : UINT8_MAX)      \
> >     +)
> >     +
> >     +#define            type_min(x)
> > (                                   \
> >     +  (sizeof(x) >= 8) ? (is_signed(x) ? INT64_MIN : 0) :      \
> >     +  (sizeof(x) >= 4) ? (is_signed(x) ? INT32_MIN : 0) :      \
> >     +  (sizeof(x) >= 2) ? (is_signed(x) ? INT16_MIN : 0) :      \
> >     +                (is_signed(x) ? INT8_MIN : 0)      \
> >     +)
> >     +
> >      #endif     /* _LINUX_KERNEL_H_ */
> > 
> > 
> >