minmax: Introduce {min,max}_array()

Introduce min_array() (resp max_array()) in order to get the
minimal (resp maximum) of values present in an array.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/20230623085830.749991-8-herve.codina@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/include/linux/minmax.h b/include/linux/minmax.h
index 396df1121bffba9e3247018ec49256f25774b76d..798c6963909fcbd6ac0df2b4cb7c20fe4d0bbf3c 100644 (file)
--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -133,6 +133,70 @@
  */
 #define max_t(type, x, y)      __careful_cmp((type)(x), (type)(y), >)
 
+/*
+ * Remove a const qualifier from integer types
+ * _Generic(foo, type-name: association, ..., default: association) performs a
+ * comparison against the foo type (not the qualified type).
+ * Do not use the const keyword in the type-name as it will not match the
+ * unqualified type of foo.
+ */
+#define __unconst_integer_type_cases(type)     \
+       unsigned type:  (unsigned type)0,       \
+       signed type:    (signed type)0
+
+#define __unconst_integer_typeof(x) typeof(                    \
+       _Generic((x),                                           \
+               char: (char)0,                                  \
+               __unconst_integer_type_cases(char),             \
+               __unconst_integer_type_cases(short),            \
+               __unconst_integer_type_cases(int),              \
+               __unconst_integer_type_cases(long),             \
+               __unconst_integer_type_cases(long long),        \
+               default: (x)))
+
+/*
+ * Do not check the array parameter using __must_be_array().
+ * In the following legit use-case where the "array" passed is a simple pointer,
+ * __must_be_array() will return a failure.
+ * --- 8< ---
+ * int *buff
+ * ...
+ * min = min_array(buff, nb_items);
+ * --- 8< ---
+ *
+ * The first typeof(&(array)[0]) is needed in order to support arrays of both
+ * 'int *buff' and 'int buff[N]' types.
+ *
+ * The array can be an array of const items.
+ * typeof() keeps the const qualifier. Use __unconst_integer_typeof() in order
+ * to discard the const qualifier for the __element variable.
+ */
+#define __minmax_array(op, array, len) ({                              \
+       typeof(&(array)[0]) __array = (array);                          \
+       typeof(len) __len = (len);                                      \
+       __unconst_integer_typeof(__array[0]) __element = __array[--__len]; \
+       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