1 files changed, 319 insertions, 0 deletions
diff --git a/include/linux/minmax.h b/include/linux/minmax.h
new file mode 100644
index 000000000000..eaaf5c008e4d
--- /dev/null
+++ b/include/linux/minmax.h
@@ -0,0 +1,319 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MINMAX_H
+#define _LINUX_MINMAX_H
+
+#include <linux/build_bug.h>
+#include <linux/compiler.h>
+#include <linux/const.h>
+#include <linux/types.h>
+
+/*
+ * min()/max()/clamp() macros must accomplish several things:
+ *
+ * - Avoid multiple evaluations of the arguments (so side-effects like
+ *   "x++" happen only once) when non-constant.
+ * - Perform signed v unsigned type-checking (to generate compile
+ *   errors instead of nasty runtime surprises).
+ * - Unsigned char/short are always promoted to signed int and can be
+ *   compared against signed or unsigned arguments.
+ * - Unsigned arguments can be compared against non-negative signed constants.
+ * - Comparison of a signed argument against an unsigned constant fails
+ *   even if the constant is below __INT_MAX__ and could be cast to int.
+ */
+#define __typecheck(x, y) \
+	(!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
+
+/*
+ * __sign_use for integer expressions:
+ *   bit #0 set if ok for unsigned comparisons
+ *   bit #1 set if ok for signed comparisons
+ *
+ * In particular, statically non-negative signed integer expressions
+ * are ok for both.
+ *
+ * NOTE! Unsigned types smaller than 'int' are implicitly converted to 'int'
+ * in expressions, and are accepted for signed conversions for now.
+ * This is debatable.
+ *
+ * Note that 'x' is the original expression, and 'ux' is the unique variable
+ * that contains the value.
+ *
+ * We use 'ux' for pure type checking, and 'x' for when we need to look at the
+ * value (but without evaluating it for side effects!
+ * Careful to only ever evaluate it with sizeof() or __builtin_constant_p() etc).
+ *
+ * Pointers end up being checked by the normal C type rules at the actual
+ * comparison, and these expressions only need to be careful to not cause
+ * warnings for pointer use.
+ */
+#define __sign_use(ux) (is_signed_type(typeof(ux)) ? \
+	(2 + __is_nonneg(ux)) : (1 + 2 * (sizeof(ux) < 4)))
+
+/*
+ * Check whether a signed value is always non-negative.
+ *
+ * A cast is needed to avoid any warnings from values that aren't signed
+ * integer types (in which case the result doesn't matter).
+ *
+ * On 64-bit any integer or pointer type can safely be cast to 'long long'.
+ * But on 32-bit we need to avoid warnings about casting pointers to integers
+ * of different sizes without truncating 64-bit values so 'long' or 'long long'
+ * must be used depending on the size of the value.
+ *
+ * This does not work for 128-bit signed integers since the cast would truncate
+ * them, but we do not use s128 types in the kernel (we do use 'u128',
+ * but they are handled by the !is_signed_type() case).
+ */
+#if __SIZEOF_POINTER__ == __SIZEOF_LONG_LONG__
+#define __is_nonneg(ux) statically_true((long long)(ux) >= 0)
+#else
+#define __is_nonneg(ux) statically_true( \
+	(typeof(__builtin_choose_expr(sizeof(ux) > 4, 1LL, 1L)))(ux) >= 0)
+#endif
+
+#define __types_ok(ux, uy) \
+	(__sign_use(ux) & __sign_use(uy))
+
+#define __types_ok3(ux, uy, uz) \
+	(__sign_use(ux) & __sign_use(uy) & __sign_use(uz))
+
+#define __cmp_op_min <
+#define __cmp_op_max >
+
+#define __cmp(op, x, y)	((x) __cmp_op_##op (y) ? (x) : (y))
+
+#define __cmp_once_unique(op, type, x, y, ux, uy) \
+	({ type ux = (x); type uy = (y); __cmp(op, ux, uy); })
+
+#define __cmp_once(op, type, x, y) \
+	__cmp_once_unique(op, type, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
+
+#define __careful_cmp_once(op, x, y, ux, uy) ({		\
+	__auto_type ux = (x); __auto_type uy = (y);	\
+	BUILD_BUG_ON_MSG(!__types_ok(ux, uy),		\
+		#op"("#x", "#y") signedness error");	\
+	__cmp(op, ux, uy); })
+
+#define __careful_cmp(op, x, y) \
+	__careful_cmp_once(op, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
+
+/**
+ * min - return minimum of two values of the same or compatible types
+ * @x: first value
+ * @y: second value
+ */
+#define min(x, y)	__careful_cmp(min, x, y)
+
+/**
+ * max - return maximum of two values of the same or compatible types
+ * @x: first value
+ * @y: second value
+ */
+#define max(x, y)	__careful_cmp(max, x, y)
+
+/**
+ * umin - return minimum of two non-negative values
+ *   Signed types are zero extended to match a larger unsigned type.
+ * @x: first value
+ * @y: second value
+ */
+#define umin(x, y)	\
+	__careful_cmp(min, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
+
+/**
+ * umax - return maximum of two non-negative values
+ * @x: first value
+ * @y: second value
+ */
+#define umax(x, y)	\
+	__careful_cmp(max, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
+
+#define __careful_op3(op, x, y, z, ux, uy, uz) ({			\
+	__auto_type ux = (x); __auto_type uy = (y);__auto_type uz = (z);\
+	BUILD_BUG_ON_MSG(!__types_ok3(ux, uy, uz),			\
+		#op"3("#x", "#y", "#z") signedness error");		\
+	__cmp(op, ux, __cmp(op, uy, uz)); })
+
+/**
+ * min3 - return minimum of three values
+ * @x: first value
+ * @y: second value
+ * @z: third value
+ */
+#define min3(x, y, z) \
+	__careful_op3(min, x, y, z, __UNIQUE_ID(x_), __UNIQUE_ID(y_), __UNIQUE_ID(z_))
+
+/**
+ * max3 - return maximum of three values
+ * @x: first value
+ * @y: second value
+ * @z: third value
+ */
+#define max3(x, y, z) \
+	__careful_op3(max, x, y, z, __UNIQUE_ID(x_), __UNIQUE_ID(y_), __UNIQUE_ID(z_))
+
+/**
+ * min_t - return minimum of two values, using the specified type
+ * @type: data type to use
+ * @x: first value
+ * @y: second value
+ */
+#define min_t(type, x, y) __cmp_once(min, type, x, y)
+
+/**
+ * max_t - return maximum of two values, using the specified type
+ * @type: data type to use
+ * @x: first value
+ * @y: second value
+ */
+#define max_t(type, x, y) __cmp_once(max, type, x, y)
+
+/**
+ * min_not_zero - return the minimum that is _not_ zero, unless both are zero
+ * @x: value1
+ * @y: value2
+ */
+#define min_not_zero(x, y) ({			\
+	typeof(x) __x = (x);			\
+	typeof(y) __y = (y);			\
+	__x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
+
+#define __clamp(val, lo, hi)	\
+	((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val)))
+
+#define __clamp_once(type, val, lo, hi, uval, ulo, uhi) ({			\
+	type uval = (val);							\
+	type ulo = (lo);							\
+	type uhi = (hi);							\
+	BUILD_BUG_ON_MSG(statically_true(ulo > uhi),				\
+		"clamp() low limit " #lo " greater than high limit " #hi);	\
+	BUILD_BUG_ON_MSG(!__types_ok3(uval, ulo, uhi),				\
+		"clamp("#val", "#lo", "#hi") signedness error");		\
+	__clamp(uval, ulo, uhi); })
+
+#define __careful_clamp(type, val, lo, hi) \
+	__clamp_once(type, val, lo, hi, __UNIQUE_ID(v_), __UNIQUE_ID(l_), __UNIQUE_ID(h_))
+
+/**
+ * clamp - return a value clamped to a given range with typechecking
+ * @val: current value
+ * @lo: lowest allowable value
+ * @hi: highest allowable value
+ *
+ * This macro checks @val/@lo/@hi to make sure they have compatible
+ * signedness.
+ */
+#define clamp(val, lo, hi) __careful_clamp(__auto_type, val, lo, hi)
+
+/**
+ * clamp_t - return a value clamped to a given range using a given type
+ * @type: the type of variable to use
+ * @val: current value
+ * @lo: minimum allowable value
+ * @hi: maximum allowable value
+ *
+ * This macro does no typechecking and uses temporary variables of type
+ * @type to make all the comparisons.
+ */
+#define clamp_t(type, val, lo, hi) __careful_clamp(type, val, lo, hi)
+
+/**
+ * clamp_val - return a value clamped to a given range using val's type
+ * @val: current value
+ * @lo: minimum allowable value
+ * @hi: maximum allowable value
+ *
+ * This macro does no typechecking and uses temporary variables of whatever
+ * type the input argument @val is.  This is useful when @val is an unsigned
+ * type and @lo and @hi are literals that will otherwise be assigned a signed
+ * integer type.
+ */
+#define clamp_val(val, lo, hi) __careful_clamp(typeof(val), val, lo, hi)
+
+/*
+ * 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 __unqual_scalar_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);					\
+	__unqual_scalar_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)
+
+static inline bool in_range64(u64 val, u64 start, u64 len)
+{
+	return (val - start) < len;
+}
+
+static inline bool in_range32(u32 val, u32 start, u32 len)
+{
+	return (val - start) < len;
+}
+
+/**
+ * in_range - Determine if a value lies within a range.
+ * @val: Value to test.
+ * @start: First value in range.
+ * @len: Number of values in range.
+ *
+ * This is more efficient than "if (start <= val && val < (start + len))".
+ * It also gives a different answer if @start + @len overflows the size of
+ * the type by a sufficient amount to encompass @val.  Decide for yourself
+ * which behaviour you want, or prove that start + len never overflow.
+ * Do not blindly replace one form with the other.
+ */
+#define in_range(val, start, len)					\
+	((sizeof(start) | sizeof(len) | sizeof(val)) <= sizeof(u32) ?	\
+		in_range32(val, start, len) : in_range64(val, start, len))
+
+/**
+ * swap - swap values of @a and @b
+ * @a: first value
+ * @b: second value
+ */
+#define swap(a, b) \
+	do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
+
+/*
+ * Use these carefully: no type checking, and uses the arguments
+ * multiple times. Use for obvious constants only.
+ */
+#define MIN(a, b) __cmp(min, a, b)
+#define MAX(a, b) __cmp(max, a, b)
+#define MIN_T(type, a, b) __cmp(min, (type)(a), (type)(b))
+#define MAX_T(type, a, b) __cmp(max, (type)(a), (type)(b))
+
+#endif	/* _LINUX_MINMAX_H */