[PATCH 1/6] kernel: add clamp(), clamp_t() and clamp_val() macros - Kernel

This is a discussion on [PATCH 1/6] kernel: add clamp(), clamp_t() and clamp_val() macros - Kernel ; Adds macros similar to min/max/min_t/max_t. Also, change the variable names used in the min/max macros to avoid shadowed variable warnings when min/max min_t/max_t are nested. clamp_val is useful when clamping to constants so all types are taken from typeof() the ...

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Thread: [PATCH 1/6] kernel: add clamp(), clamp_t() and clamp_val() macros

  1. [PATCH 1/6] kernel: add clamp(), clamp_t() and clamp_val() macros

    Adds macros similar to min/max/min_t/max_t.

    Also, change the variable names used in the min/max macros to
    avoid shadowed variable warnings when min/max min_t/max_t are
    nested.

    clamp_val is useful when clamping to constants so all types are
    taken from typeof() the first arg.

    Small formatting changes to make all the macros have a similar
    form.

    Signed-off-by: Harvey Harrison
    ---
    Andrew, this is a rollup of my original patch already in -mm with
    checkpatch warnings fixed up and one additional macro based on
    limit_value found in the b43 driver, called clamp_val.

    clamp_t is no longer used, but I introduce it anyway as some future
    user may want to force the return type similar to how min_t/max_t
    operate.

    include/linux/kernel.h | 66 ++++++++++++++++++++++++++++++++++-------------
    1 files changed, 48 insertions(+), 18 deletions(-)

    diff --git a/include/linux/kernel.h b/include/linux/kernel.h
    index 2df44e7..b9331ac 100644
    --- a/include/linux/kernel.h
    +++ b/include/linux/kernel.h
    @@ -335,33 +335,63 @@ static inline int __attribute__ ((format (printf, 1, 2))) pr_debug(const char *
    #endif /* __LITTLE_ENDIAN */

    /*
    - * min()/max() macros that also do
    + * min()/max()/clamp() macros that also do
    * strict type-checking.. See the
    * "unnecessary" pointer comparison.
    */
    -#define min(x,y) ({ \
    - typeof(x) _x = (x); \
    - typeof(y) _y = (y); \
    - (void) (&_x == &_y); \
    - _x < _y ? _x : _y; })
    -
    -#define max(x,y) ({ \
    - typeof(x) _x = (x); \
    - typeof(y) _y = (y); \
    - (void) (&_x == &_y); \
    - _x > _y ? _x : _y; })
    +#define min(x, y) ({ \
    + typeof(x) _min1 = (x); \
    + typeof(y) _min2 = (y); \
    + (void) (&_min1 == &_min2); \
    + _min1 < _min2 ? _min1 : _min2; })
    +
    +#define max(x, y) ({ \
    + typeof(x) _max1 = (x); \
    + typeof(y) _max2 = (y); \
    + (void) (&_max1 == &_max2); \
    + _max1 > _max2 ? _max1 : _max2; })
    +
    +#define clamp(val, min, max) ({ \
    + typeof(val) __val = (val); \
    + typeof(min) __min = (min); \
    + typeof(max) __max = (max); \
    + (void) (&__val == &__min); \
    + (void) (&__val == &__max); \
    + __val = __val < __min ? __min: __val; \
    + __val > __max ? __max: __val; })
    +
    +/*
    + * Useful when min and max are constants.
    + */
    +#define clamp_val(val, min, max) ({ \
    + typeof(val) __val = (val); \
    + typeof(val) __min = (min); \
    + typeof(val) __max = (max); \
    + __val = __val < __min ? __min: __val; \
    + __val > __max ? __max: __val; })

    /*
    * ..and if you can't take the strict
    * types, you can specify one yourself.
    *
    - * Or not use min/max at all, of course.
    + * Or not use min/max/clamp at all, of course.
    */
    -#define min_t(type,x,y) \
    - ({ type __x = (x); type __y = (y); __x < __y ? __x: __y; })
    -#define max_t(type,x,y) \
    - ({ type __x = (x); type __y = (y); __x > __y ? __x: __y; })
    -
    +#define min_t(type, x, y) ({ \
    + type __min1 = (x); \
    + type __min2 = (y); \
    + __min1 < __min2 ? __min1: __min2; })
    +
    +#define max_t(type, x, y) ({ \
    + type __max1 = (x); \
    + type __max2 = (y); \
    + __max1 > __max2 ? __max1: __max2; })
    +
    +#define clamp_t(type, val, min, max) ({ \
    + type __val = (val); \
    + type __min = (min); \
    + type __max = (max); \
    + __val = __val < __min ? __min: __val; \
    + __val > __max ? __max: __val; })

    /**
    * container_of - cast a member of a structure out to the containing structure
    --
    1.5.4.4.592.g32d4c


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  2. Re: [PATCH 1/6] kernel: add clamp(), clamp_t() and clamp_val() macros

    On Tue, 11 Mar 2008 14:11:34 -0700 Harvey Harrison wrote:

    > Adds macros similar to min/max/min_t/max_t.
    >
    > Also, change the variable names used in the min/max macros to
    > avoid shadowed variable warnings when min/max min_t/max_t are
    > nested.
    >
    > clamp_val is useful when clamping to constants so all types are
    > taken from typeof() the first arg.
    >
    > Small formatting changes to make all the macros have a similar
    > form.
    >
    > Signed-off-by: Harvey Harrison
    > ---
    > Andrew, this is a rollup of my original patch already in -mm with
    > checkpatch warnings fixed up and one additional macro based on
    > limit_value found in the b43 driver, called clamp_val.


    Well, this is why I dislike replacement patches. You don't know what
    changed, and the replacement patch can fail to incproporate fixes from
    third parties.

    > include/linux/kernel.h | 66 ++++++++++++++++++++++++++++++++++-------------
    > 1 files changed, 48 insertions(+), 18 deletions(-)


    And so it did. You lost my patch which removes the clamp() implementation
    from v4l. Instead it seems that you put it into [2/6]. Which means that
    this patch on its own will break the build, thus screwing up life for
    git-bisect users.

    Please don't screw up git-bisect users' lives.

    > clamp_t is no longer used, but I introduce it anyway as some future
    > user may want to force the return type similar to how min_t/max_t
    > operate.


    eh, just nuke it.

    > 1.5.4.4.592.g32d4c


    Is all this new infrastructure actually used? We seem to be adding more
    complexity than we're taking away.

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  3. Re: [PATCH 1/6] kernel: add clamp(), clamp_t() and clamp_val() macros

    On Tuesday 11 March 2008 22:11:34 Harvey Harrison wrote:
    > Adds macros similar to min/max/min_t/max_t.
    >
    > Also, change the variable names used in the min/max macros to
    > avoid shadowed variable warnings when min/max min_t/max_t are
    > nested.
    >
    > clamp_val is useful when clamping to constants so all types are
    > taken from typeof() the first arg.
    >
    > Small formatting changes to make all the macros have a similar
    > form.
    >
    > Signed-off-by: Harvey Harrison
    > ---
    > Andrew, this is a rollup of my original patch already in -mm with
    > checkpatch warnings fixed up and one additional macro based on
    > limit_value found in the b43 driver, called clamp_val.
    >
    > clamp_t is no longer used, but I introduce it anyway as some future
    > user may want to force the return type similar to how min_t/max_t
    > operate.
    >
    > include/linux/kernel.h | 66 ++++++++++++++++++++++++++++++++++-------------
    > 1 files changed, 48 insertions(+), 18 deletions(-)
    >
    > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
    > index 2df44e7..b9331ac 100644
    > --- a/include/linux/kernel.h
    > +++ b/include/linux/kernel.h
    > @@ -335,33 +335,63 @@ static inline int __attribute__ ((format (printf, 1, 2))) pr_debug(const char *
    > #endif /* __LITTLE_ENDIAN */
    >
    > /*
    > - * min()/max() macros that also do
    > + * min()/max()/clamp() macros that also do
    > * strict type-checking.. See the
    > * "unnecessary" pointer comparison.
    > */
    > -#define min(x,y) ({ \
    > - typeof(x) _x = (x); \
    > - typeof(y) _y = (y); \
    > - (void) (&_x == &_y); \
    > - _x < _y ? _x : _y; })
    > -
    > -#define max(x,y) ({ \
    > - typeof(x) _x = (x); \
    > - typeof(y) _y = (y); \
    > - (void) (&_x == &_y); \
    > - _x > _y ? _x : _y; })
    > +#define min(x, y) ({ \
    > + typeof(x) _min1 = (x); \
    > + typeof(y) _min2 = (y); \
    > + (void) (&_min1 == &_min2); \
    > + _min1 < _min2 ? _min1 : _min2; })
    > +
    > +#define max(x, y) ({ \
    > + typeof(x) _max1 = (x); \
    > + typeof(y) _max2 = (y); \
    > + (void) (&_max1 == &_max2); \
    > + _max1 > _max2 ? _max1 : _max2; })
    > +
    > +#define clamp(val, min, max) ({ \
    > + typeof(val) __val = (val); \
    > + typeof(min) __min = (min); \
    > + typeof(max) __max = (max); \
    > + (void) (&__val == &__min); \
    > + (void) (&__val == &__max); \
    > + __val = __val < __min ? __min: __val; \
    > + __val > __max ? __max: __val; })
    > +
    > +/*
    > + * Useful when min and max are constants.
    > + */
    > +#define clamp_val(val, min, max) ({ \


    So why not call it clamp_const()?
    One could even use __builtin_constant_p() and make clamp() use
    either clamp_const() or clamp_nonconst() from above automagically.
    I'd prefer that.

    > + typeof(val) __val = (val); \
    > + typeof(val) __min = (min); \
    > + typeof(val) __max = (max); \
    > + __val = __val < __min ? __min: __val; \
    > + __val > __max ? __max: __val; })
    >
    > /*
    > * ..and if you can't take the strict
    > * types, you can specify one yourself.
    > *
    > - * Or not use min/max at all, of course.
    > + * Or not use min/max/clamp at all, of course.
    > */
    > -#define min_t(type,x,y) \
    > - ({ type __x = (x); type __y = (y); __x < __y ? __x: __y; })
    > -#define max_t(type,x,y) \
    > - ({ type __x = (x); type __y = (y); __x > __y ? __x: __y; })
    > -
    > +#define min_t(type, x, y) ({ \
    > + type __min1 = (x); \
    > + type __min2 = (y); \
    > + __min1 < __min2 ? __min1: __min2; })
    > +
    > +#define max_t(type, x, y) ({ \
    > + type __max1 = (x); \
    > + type __max2 = (y); \
    > + __max1 > __max2 ? __max1: __max2; })
    > +
    > +#define clamp_t(type, val, min, max) ({ \
    > + type __val = (val); \
    > + type __min = (min); \
    > + type __max = (max); \
    > + __val = __val < __min ? __min: __val; \
    > + __val > __max ? __max: __val; })
    >
    > /**
    > * container_of - cast a member of a structure out to the containing structure




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  4. Re: [PATCH 1/6] kernel: add clamp(), clamp_t() and clamp_val() macros

    On Wed, 2008-03-12 at 16:13 +0100, Michael Buesch wrote:
    > So why not call it clamp_const()?
    > One could even use __builtin_constant_p() and make clamp() use
    > either clamp_const() or clamp_nonconst() from above automagically.
    > I'd prefer that.


    Did you mean something like this? No more clamp_val, just clamp and
    clamp_t. clamp_t forces all the types, clamp looks at the min and max
    args, and if they are constants, uses the type of val instead. If not
    a constant, the strict typechecking is done.

    From: Harvey Harrison
    Subject: [PATCH] kernel: add clamp(), clamp_t() macros

    Adds macros similar to min/max/min_t/max_t.

    Also, change the variable names used in the min/max macros to
    avoid shadowed variable warnings when min/max min_t/max_t are
    nested.

    Small formatting changes to make all the macros have a similar
    form.

    Signed-off-by: Harvey Harrison
    ---
    include/linux/kernel.h | 68 +++++++++++++++++++++++++++++++++++------------
    1 files changed, 50 insertions(+), 18 deletions(-)

    diff --git a/include/linux/kernel.h b/include/linux/kernel.h
    index 2df44e7..0d4cb5f 100644
    --- a/include/linux/kernel.h
    +++ b/include/linux/kernel.h
    @@ -335,33 +335,65 @@ static inline int __attribute__ ((format (printf, 1, 2))) pr_debug(const char *
    #endif /* __LITTLE_ENDIAN */

    /*
    - * min()/max() macros that also do
    + * min()/max()/clamp() macros that also do
    * strict type-checking.. See the
    * "unnecessary" pointer comparison.
    */
    -#define min(x,y) ({ \
    - typeof(x) _x = (x); \
    - typeof(y) _y = (y); \
    - (void) (&_x == &_y); \
    - _x < _y ? _x : _y; })
    -
    -#define max(x,y) ({ \
    - typeof(x) _x = (x); \
    - typeof(y) _y = (y); \
    - (void) (&_x == &_y); \
    - _x > _y ? _x : _y; })
    +#define min(x, y) ({ \
    + typeof(x) _min1 = (x); \
    + typeof(y) _min2 = (y); \
    + (void) (&_min1 == &_min2); \
    + _min1 < _min2 ? _min1 : _min2; })
    +
    +#define max(x, y) ({ \
    + typeof(x) _max1 = (x); \
    + typeof(y) _max2 = (y); \
    + (void) (&_max1 == &_max2); \
    + _max1 > _max2 ? _max1 : _max2; })
    +
    +#define clamp(val, min, max) ({ \
    + typeof(val) __val = (val); \
    + \
    + if (__builtin_constant_p(min)) { \
    + typeof(val) __min = (min); \
    + __val = __val < __min ? __min: __val; \
    + } else { \
    + typeof(min) __min = (min); \
    + (void) (&__val == &__min); \
    + __val = __val < __min ? __min: __val; \
    + } \
    + \
    + if (__builtin_constant_p(max)) { \
    + typeof(val) __max = (max); \
    + __val > __max ? __max: __val; \
    + } else { \
    + typeof(max) __max = (max); \
    + (void) (&__val == &__max); \
    + __val > __max ? __max: __val; \
    + } })

    /*
    * ..and if you can't take the strict
    * types, you can specify one yourself.
    *
    - * Or not use min/max at all, of course.
    + * Or not use min/max/clamp at all, of course.
    */
    -#define min_t(type,x,y) \
    - ({ type __x = (x); type __y = (y); __x < __y ? __x: __y; })
    -#define max_t(type,x,y) \
    - ({ type __x = (x); type __y = (y); __x > __y ? __x: __y; })
    -
    +#define min_t(type, x, y) ({ \
    + type __min1 = (x); \
    + type __min2 = (y); \
    + __min1 < __min2 ? __min1: __min2; })
    +
    +#define max_t(type, x, y) ({ \
    + type __max1 = (x); \
    + type __max2 = (y); \
    + __max1 > __max2 ? __max1: __max2; })
    +
    +#define clamp_t(type, val, min, max) ({ \
    + type __val = (val); \
    + type __min = (min); \
    + type __max = (max); \
    + __val = __val < __min ? __min: __val; \
    + __val > __max ? __max: __val; })

    /**
    * container_of - cast a member of a structure out to the containing structure
    --
    1.5.4.4.592.g32d4c



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  5. Re: [PATCH 1/6] kernel: add clamp(), clamp_t() and clamp_val() macros

    On Wednesday 12 March 2008 17:54:26 Harvey Harrison wrote:
    > On Wed, 2008-03-12 at 16:13 +0100, Michael Buesch wrote:
    > > So why not call it clamp_const()?
    > > One could even use __builtin_constant_p() and make clamp() use
    > > either clamp_const() or clamp_nonconst() from above automagically.
    > > I'd prefer that.

    >
    > Did you mean something like this? No more clamp_val, just clamp and
    > clamp_t. clamp_t forces all the types, clamp looks at the min and max
    > args, and if they are constants, uses the type of val instead. If not
    > a constant, the strict typechecking is done.


    > +#define clamp(val, min, max) ({ \
    > + typeof(val) __val = (val); \
    > + \
    > + if (__builtin_constant_p(min)) { \
    > + typeof(val) __min = (min); \
    > + __val = __val < __min ? __min: __val; \
    > + } else { \
    > + typeof(min) __min = (min); \
    > + (void) (&__val == &__min); \
    > + __val = __val < __min ? __min: __val; \
    > + } \
    > + \
    > + if (__builtin_constant_p(max)) { \
    > + typeof(val) __max = (max); \
    > + __val > __max ? __max: __val; \
    > + } else { \
    > + typeof(max) __max = (max); \
    > + (void) (&__val == &__max); \
    > + __val > __max ? __max: __val; \
    > + } })


    Yeah, something like that.
    Does returning of the value work over an indentation level, too?
    I dunno this detail of the language.
    But I'd prefer the following for readability anyway:

    + if (__builtin_constant_p(max)) { \
    + typeof(val) __max = (max); \
    + __val = __val > __max ? __max: __val; \
    + } else { \
    + typeof(max) __max = (max); \
    + (void) (&__val == &__max); \
    + __val = __val > __max ? __max: __val; \
    + }
    + __val; })

    Probably you can also only put the pointer check into the constant check:

    +#define clamp(val, min, max) ({ \
    + typeof(val) __val = (val); \
    + typeof(min) __min = (min); \
    + typeof(max) __max = (max); \
    + if (!__builtin_constant_p(min)) \
    + (void) (&__val == &__min); \
    + __val = __val < __min ? __min: __val; \
    + if (!__builtin_constant_p(max)) \
    + (void) (&__val == &__max); \
    + __val = __val > __max ? __max: __val; \
    + __val; })

    But it seems that this evaluates the arguments twice, so my idea turns out
    to be not too good anyway. hm..

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  6. Re: [PATCH 1/6] kernel: add clamp(), clamp_t() and clamp_val() macros

    On Wed, 2008-03-12 at 18:20 +0100, Michael Buesch wrote:
    > On Wednesday 12 March 2008 17:54:26 Harvey Harrison wrote:
    > > On Wed, 2008-03-12 at 16:13 +0100, Michael Buesch wrote:
    > > > So why not call it clamp_const()?
    > > > One could even use __builtin_constant_p() and make clamp() use
    > > > either clamp_const() or clamp_nonconst() from above automagically.
    > > > I'd prefer that.

    > >
    > > Did you mean something like this? No more clamp_val, just clamp and
    > > clamp_t. clamp_t forces all the types, clamp looks at the min and max
    > > args, and if they are constants, uses the type of val instead. If not
    > > a constant, the strict typechecking is done.

    >
    > > +#define clamp(val, min, max) ({ \
    > > + typeof(val) __val = (val); \
    > > + \
    > > + if (__builtin_constant_p(min)) { \
    > > + typeof(val) __min = (min); \
    > > + __val = __val < __min ? __min: __val; \
    > > + } else { \
    > > + typeof(min) __min = (min); \
    > > + (void) (&__val == &__min); \
    > > + __val = __val < __min ? __min: __val; \
    > > + } \
    > > + \
    > > + if (__builtin_constant_p(max)) { \
    > > + typeof(val) __max = (max); \
    > > + __val > __max ? __max: __val; \
    > > + } else { \
    > > + typeof(max) __max = (max); \
    > > + (void) (&__val == &__max); \
    > > + __val > __max ? __max: __val; \
    > > + } })

    >
    > Yeah, something like that.
    > Does returning of the value work over an indentation level, too?
    > I dunno this detail of the language.
    > But I'd prefer the following for readability anyway:
    >
    > + if (__builtin_constant_p(max)) { \
    > + typeof(val) __max = (max); \
    > + __val = __val > __max ? __max: __val; \
    > + } else { \
    > + typeof(max) __max = (max); \
    > + (void) (&__val == &__max); \
    > + __val = __val > __max ? __max: __val; \
    > + }
    > + __val; })


    Yeah, that is better. (and even works).

    Harvey

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