linux-kernel - Re: [PATCH v3 06/12] minmax: Introduce {min,max}

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Date:   Tue, 13 Jun 2023 10:00:00 +0200
From:   Herve Codina <herve.codina@...tlin.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        alsa-devel@...a-project.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v3 06/12] minmax: Introduce {min,max}_array()

Hi Andy,

On Mon, 12 Jun 2023 17:10:40 +0300
Andy Shevchenko <andy.shevchenko@...il.com> wrote:

> On Mon, Jun 12, 2023 at 3:30 PM Herve Codina <herve.codina@...tlin.com> wrote:
> >
> > Introduce min_array() (resp max_array()) in order to get the
> > minimal (resp maximum) of values present in an array.  
> 
> Some comments below, after addressing them,
> Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
> 
> > Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> > ---
> >  include/linux/minmax.h | 26 ++++++++++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> >
> > diff --git a/include/linux/minmax.h b/include/linux/minmax.h
> > index 396df1121bff..37a211f22404 100644
> > --- a/include/linux/minmax.h
> > +++ b/include/linux/minmax.h
> > @@ -133,6 +133,32 @@
> >   */
> >  #define max_t(type, x, y)      __careful_cmp((type)(x), (type)(y), >)
> >
> > +#define __minmax_array(op, array, len) ({                      \  
> 
> Maybe it's my MUA, maybe the code contains spaces, can you switch to
> TABs if it's the case?
> 
> > +       typeof(array) __array = (array);                        \  
> 
> We have __must_be_array()

Using __must_be_array() will lead to some failure.
Indeed, we can have:
  --- 8< ---
  int *buff
  ...
  min = min_array(buff, nb_item);
  --- 8< ---

In this case, __must_be_array() will report that buff is not an array.

To avoid any confusion, what do you think if I renamed {min,max}_array()
to {min,max}_buffer() and replace __array by __buff and use *(__buff + xxx)
instead of array[xxx] in the macro.

This will lead to:
--- 8< ---
#define __minmax_buffer(op, buff, len) ({			\
	typeof(buff) __buff = (buff);			\
	typeof(len) __len = (len);				\
	typeof(*buff + 0) __element = *(__buff + --__len);	\
	while (__len--)						\
		__element = op(__element, *(__buff + __len]));	\
	__element; })

#define min_buffer(buffer, len) __minmax_array(min, buffer, len)
#define max_buffer(buffer, len) __minmax_array(max, buffer, len)
--- 8< ---

Regards,
Hervé

> 
> You will need to fix the inclusions in minmax.h at the same time, it needs
> linux/build_bug.h (which includes compiler.h needed for __UNIQUE_ID()
> and for the above mentioned one).
> 
> > +       typeof(len) __len = (len);                              \
> > +       typeof(*__array + 0) __element = __array[--__len];      \  
> 
> After above, this can be written as __array[0].
> 
> > +       while (__len--)                                         \
> > +               __element = op(__element, __array[__len]);      \
> > +       __element; })
> > +
> > +/**
> > + * min_array - return minimum of values present in an array
> > + * @array: array
> > + * @len: array length
> > + *
> > + * Note that @len must not be zero (empty array).
> > + */
> > +#define min_array(array, len) __minmax_array(min, array, len)
> > +
> > +/**
> > + * max_array - return maximum of values present in an array
> > + * @array: array
> > + * @len: array length
> > + *
> > + * Note that @len must not be zero (empty array).
> > + */
> > +#define max_array(array, len) __minmax_array(max, array, len)
> > +
> >  /**
> >   * clamp_t - return a value clamped to a given range using a given type
> >   * @type: the type of variable to use  
>