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

[Ravi Pokala]

From: <owner-src-committers at freebsd.org> on behalf of Warner Losh <imp at bsdimp.com>
Date: 2020-06-29, Monday at 13:26
To: Ravi Pokala <rpokala at freebsd.org>
Cc: Hans Petter Selasky <hselasky at freebsd.org>, src-committers <src-committers at freebsd.org>, <svn-src-all at freebsd.org>, <svn-src-head at freebsd.org>
Subject: Re: svn commit: r362781 - head/sys/compat/linuxkpi/common/include/linux

 

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?

 

Letters are cheap now, Warner; we can afford to spell out "type". :-)

 

-Ravi (rpokala@)

 

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_ */