1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_MINMAX_H
3 #define _LINUX_MINMAX_H
5 #include <linux/compiler.h>
6 #include <linux/const.h>
7 #include <linux/types.h>
10 * min()/max()/clamp() macros must accomplish three things:
12 * - Avoid multiple evaluations of the arguments (so side-effects like
13 * "x++" happen only once) when non-constant.
14 * - Retain result as a constant expressions when called with only
15 * constant expressions (to avoid tripping VLA warnings in stack
17 * - Perform signed v unsigned type-checking (to generate compile
18 * errors instead of nasty runtime surprises).
19 * - Unsigned char/short are always promoted to signed int and can be
20 * compared against signed or unsigned arguments.
21 * - Unsigned arguments can be compared against non-negative signed constants.
22 * - Comparison of a signed argument against an unsigned constant fails
23 * even if the constant is below __INT_MAX__ and could be cast to int.
25 #define __typecheck(x, y) \
26 (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
28 /* is_signed_type() isn't a constexpr for pointer types */
29 #define __is_signed(x) \
30 __builtin_choose_expr(__is_constexpr(is_signed_type(typeof(x))), \
31 is_signed_type(typeof(x)), 0)
33 /* True for a non-negative signed int constant */
34 #define __is_noneg_int(x) \
35 (__builtin_choose_expr(__is_constexpr(x) && __is_signed(x), x, -1) >= 0)
37 #define __types_ok(x, y) \
38 (__is_signed(x) == __is_signed(y) || \
39 __is_signed((x) + 0) == __is_signed((y) + 0) || \
40 __is_noneg_int(x) || __is_noneg_int(y))
42 #define __cmp_op_min <
43 #define __cmp_op_max >
45 #define __cmp(op, x, y) ((x) __cmp_op_##op (y) ? (x) : (y))
47 #define __cmp_once(op, x, y, unique_x, unique_y) ({ \
48 typeof(x) unique_x = (x); \
49 typeof(y) unique_y = (y); \
50 static_assert(__types_ok(x, y), \
51 #op "(" #x ", " #y ") signedness error, fix types or consider u" #op "() before " #op "_t()"); \
52 __cmp(op, unique_x, unique_y); })
54 #define __careful_cmp(op, x, y) \
55 __builtin_choose_expr(__is_constexpr((x) - (y)), \
57 __cmp_once(op, x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y)))
59 #define __clamp(val, lo, hi) \
60 ((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val)))
62 #define __clamp_once(val, lo, hi, unique_val, unique_lo, unique_hi) ({ \
63 typeof(val) unique_val = (val); \
64 typeof(lo) unique_lo = (lo); \
65 typeof(hi) unique_hi = (hi); \
66 static_assert(__builtin_choose_expr(__is_constexpr((lo) > (hi)), \
67 (lo) <= (hi), true), \
68 "clamp() low limit " #lo " greater than high limit " #hi); \
69 static_assert(__types_ok(val, lo), "clamp() 'lo' signedness error"); \
70 static_assert(__types_ok(val, hi), "clamp() 'hi' signedness error"); \
71 __clamp(unique_val, unique_lo, unique_hi); })
73 #define __careful_clamp(val, lo, hi) ({ \
74 __builtin_choose_expr(__is_constexpr((val) - (lo) + (hi)), \
75 __clamp(val, lo, hi), \
76 __clamp_once(val, lo, hi, __UNIQUE_ID(__val), \
77 __UNIQUE_ID(__lo), __UNIQUE_ID(__hi))); })
80 * min - return minimum of two values of the same or compatible types
84 #define min(x, y) __careful_cmp(min, x, y)
87 * max - return maximum of two values of the same or compatible types
91 #define max(x, y) __careful_cmp(max, x, y)
94 * umin - return minimum of two non-negative values
95 * Signed types are zero extended to match a larger unsigned type.
100 __careful_cmp(min, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
103 * umax - return maximum of two non-negative values
108 __careful_cmp(max, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
111 * min3 - return minimum of three values
116 #define min3(x, y, z) min((typeof(x))min(x, y), z)
119 * max3 - return maximum of three values
124 #define max3(x, y, z) max((typeof(x))max(x, y), z)
127 * min_not_zero - return the minimum that is _not_ zero, unless both are zero
131 #define min_not_zero(x, y) ({ \
132 typeof(x) __x = (x); \
133 typeof(y) __y = (y); \
134 __x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
137 * clamp - return a value clamped to a given range with strict typechecking
138 * @val: current value
139 * @lo: lowest allowable value
140 * @hi: highest allowable value
142 * This macro does strict typechecking of @lo/@hi to make sure they are of the
143 * same type as @val. See the unnecessary pointer comparisons.
145 #define clamp(val, lo, hi) __careful_clamp(val, lo, hi)
148 * ..and if you can't take the strict
149 * types, you can specify one yourself.
151 * Or not use min/max/clamp at all, of course.
155 * min_t - return minimum of two values, using the specified type
156 * @type: data type to use
160 #define min_t(type, x, y) __careful_cmp(min, (type)(x), (type)(y))
163 * max_t - return maximum of two values, using the specified type
164 * @type: data type to use
168 #define max_t(type, x, y) __careful_cmp(max, (type)(x), (type)(y))
171 * Do not check the array parameter using __must_be_array().
172 * In the following legit use-case where the "array" passed is a simple pointer,
173 * __must_be_array() will return a failure.
177 * min = min_array(buff, nb_items);
180 * The first typeof(&(array)[0]) is needed in order to support arrays of both
181 * 'int *buff' and 'int buff[N]' types.
183 * The array can be an array of const items.
184 * typeof() keeps the const qualifier. Use __unqual_scalar_typeof() in order
185 * to discard the const qualifier for the __element variable.
187 #define __minmax_array(op, array, len) ({ \
188 typeof(&(array)[0]) __array = (array); \
189 typeof(len) __len = (len); \
190 __unqual_scalar_typeof(__array[0]) __element = __array[--__len];\
192 __element = op(__element, __array[__len]); \
196 * min_array - return minimum of values present in an array
200 * Note that @len must not be zero (empty array).
202 #define min_array(array, len) __minmax_array(min, array, len)
205 * max_array - return maximum of values present in an array
209 * Note that @len must not be zero (empty array).
211 #define max_array(array, len) __minmax_array(max, array, len)
214 * clamp_t - return a value clamped to a given range using a given type
215 * @type: the type of variable to use
216 * @val: current value
217 * @lo: minimum allowable value
218 * @hi: maximum allowable value
220 * This macro does no typechecking and uses temporary variables of type
221 * @type to make all the comparisons.
223 #define clamp_t(type, val, lo, hi) __careful_clamp((type)(val), (type)(lo), (type)(hi))
226 * clamp_val - return a value clamped to a given range using val's type
227 * @val: current value
228 * @lo: minimum allowable value
229 * @hi: maximum allowable value
231 * This macro does no typechecking and uses temporary variables of whatever
232 * type the input argument @val is. This is useful when @val is an unsigned
233 * type and @lo and @hi are literals that will otherwise be assigned a signed
236 #define clamp_val(val, lo, hi) clamp_t(typeof(val), val, lo, hi)
238 static inline bool in_range64(u64 val, u64 start, u64 len)
240 return (val - start) < len;
243 static inline bool in_range32(u32 val, u32 start, u32 len)
245 return (val - start) < len;
249 * in_range - Determine if a value lies within a range.
250 * @val: Value to test.
251 * @start: First value in range.
252 * @len: Number of values in range.
254 * This is more efficient than "if (start <= val && val < (start + len))".
255 * It also gives a different answer if @start + @len overflows the size of
256 * the type by a sufficient amount to encompass @val. Decide for yourself
257 * which behaviour you want, or prove that start + len never overflow.
258 * Do not blindly replace one form with the other.
260 #define in_range(val, start, len) \
261 ((sizeof(start) | sizeof(len) | sizeof(val)) <= sizeof(u32) ? \
262 in_range32(val, start, len) : in_range64(val, start, len))
265 * swap - swap values of @a and @b
270 do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
272 #endif /* _LINUX_MINMAX_H */