1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_MINMAX_H
3#define _LINUX_MINMAX_H
4
5#include <linux/build_bug.h>
6#include <linux/compiler.h>
7#include <linux/const.h>
8#include <linux/types.h>
9
10/*
11 * min()/max()/clamp() macros must accomplish three things:
12 *
13 * - Avoid multiple evaluations of the arguments (so side-effects like
14 * "x++" happen only once) when non-constant.
15 * - Retain result as a constant expressions when called with only
16 * constant expressions (to avoid tripping VLA warnings in stack
17 * allocation usage).
18 * - Perform signed v unsigned type-checking (to generate compile
19 * errors instead of nasty runtime surprises).
20 * - Unsigned char/short are always promoted to signed int and can be
21 * compared against signed or unsigned arguments.
22 * - Unsigned arguments can be compared against non-negative signed constants.
23 * - Comparison of a signed argument against an unsigned constant fails
24 * even if the constant is below __INT_MAX__ and could be cast to int.
25 */
26#define __typecheck(x, y) \
27 (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
28
29/* is_signed_type() isn't a constexpr for pointer types */
30#define __is_signed(x) \
31 __builtin_choose_expr(__is_constexpr(is_signed_type(typeof(x))), \
32 is_signed_type(typeof(x)), 0)
33
34/* True for a non-negative signed int constant */
35#define __is_noneg_int(x) \
36 (__builtin_choose_expr(__is_constexpr(x) && __is_signed(x), x, -1) >= 0)
37
38#define __types_ok(x, y) \
39 (__is_signed(x) == __is_signed(y) || \
40 __is_signed((x) + 0) == __is_signed((y) + 0) || \
41 __is_noneg_int(x) || __is_noneg_int(y))
42
43#define __cmp_op_min <
44#define __cmp_op_max >
45
46#define __cmp(op, x, y) ((x) __cmp_op_##op (y) ? (x) : (y))
47
48#define __cmp_once(op, x, y, unique_x, unique_y) ({ \
49 typeof(x) unique_x = (x); \
50 typeof(y) unique_y = (y); \
51 static_assert(__types_ok(x, y), \
52 #op "(" #x ", " #y ") signedness error, fix types or consider u" #op "() before " #op "_t()"); \
53 __cmp(op, unique_x, unique_y); })
54
55#define __careful_cmp(op, x, y) \
56 __builtin_choose_expr(__is_constexpr((x) - (y)), \
57 __cmp(op, x, y), \
58 __cmp_once(op, x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y)))
59
60#define __clamp(val, lo, hi) \
61 ((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val)))
62
63#define __clamp_once(val, lo, hi, unique_val, unique_lo, unique_hi) ({ \
64 typeof(val) unique_val = (val); \
65 typeof(lo) unique_lo = (lo); \
66 typeof(hi) unique_hi = (hi); \
67 static_assert(__builtin_choose_expr(__is_constexpr((lo) > (hi)), \
68 (lo) <= (hi), true), \
69 "clamp() low limit " #lo " greater than high limit " #hi); \
70 static_assert(__types_ok(val, lo), "clamp() 'lo' signedness error"); \
71 static_assert(__types_ok(val, hi), "clamp() 'hi' signedness error"); \
72 __clamp(unique_val, unique_lo, unique_hi); })
73
74#define __careful_clamp(val, lo, hi) ({ \
75 __builtin_choose_expr(__is_constexpr((val) - (lo) + (hi)), \
76 __clamp(val, lo, hi), \
77 __clamp_once(val, lo, hi, __UNIQUE_ID(__val), \
78 __UNIQUE_ID(__lo), __UNIQUE_ID(__hi))); })
79
80/**
81 * min - return minimum of two values of the same or compatible types
82 * @x: first value
83 * @y: second value
84 */
85#define min(x, y) __careful_cmp(min, x, y)
86
87/**
88 * max - return maximum of two values of the same or compatible types
89 * @x: first value
90 * @y: second value
91 */
92#define max(x, y) __careful_cmp(max, x, y)
93
94/**
95 * umin - return minimum of two non-negative values
96 * Signed types are zero extended to match a larger unsigned type.
97 * @x: first value
98 * @y: second value
99 */
100#define umin(x, y) \
101 __careful_cmp(min, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
102
103/**
104 * umax - return maximum of two non-negative values
105 * @x: first value
106 * @y: second value
107 */
108#define umax(x, y) \
109 __careful_cmp(max, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
110
111/**
112 * min3 - return minimum of three values
113 * @x: first value
114 * @y: second value
115 * @z: third value
116 */
117#define min3(x, y, z) min((typeof(x))min(x, y), z)
118
119/**
120 * max3 - return maximum of three values
121 * @x: first value
122 * @y: second value
123 * @z: third value
124 */
125#define max3(x, y, z) max((typeof(x))max(x, y), z)
126
127/**
128 * min_not_zero - return the minimum that is _not_ zero, unless both are zero
129 * @x: value1
130 * @y: value2
131 */
132#define min_not_zero(x, y) ({ \
133 typeof(x) __x = (x); \
134 typeof(y) __y = (y); \
135 __x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
136
137/**
138 * clamp - return a value clamped to a given range with strict typechecking
139 * @val: current value
140 * @lo: lowest allowable value
141 * @hi: highest allowable value
142 *
143 * This macro does strict typechecking of @lo/@hi to make sure they are of the
144 * same type as @val. See the unnecessary pointer comparisons.
145 */
146#define clamp(val, lo, hi) __careful_clamp(val, lo, hi)
147
148/*
149 * ..and if you can't take the strict
150 * types, you can specify one yourself.
151 *
152 * Or not use min/max/clamp at all, of course.
153 */
154
155/**
156 * min_t - return minimum of two values, using the specified type
157 * @type: data type to use
158 * @x: first value
159 * @y: second value
160 */
161#define min_t(type, x, y) __careful_cmp(min, (type)(x), (type)(y))
162
163/**
164 * max_t - return maximum of two values, using the specified type
165 * @type: data type to use
166 * @x: first value
167 * @y: second value
168 */
169#define max_t(type, x, y) __careful_cmp(max, (type)(x), (type)(y))
170
171/*
172 * Do not check the array parameter using __must_be_array().
173 * In the following legit use-case where the "array" passed is a simple pointer,
174 * __must_be_array() will return a failure.
175 * --- 8< ---
176 * int *buff
177 * ...
178 * min = min_array(buff, nb_items);
179 * --- 8< ---
180 *
181 * The first typeof(&(array)[0]) is needed in order to support arrays of both
182 * 'int *buff' and 'int buff[N]' types.
183 *
184 * The array can be an array of const items.
185 * typeof() keeps the const qualifier. Use __unqual_scalar_typeof() in order
186 * to discard the const qualifier for the __element variable.
187 */
188#define __minmax_array(op, array, len) ({ \
189 typeof(&(array)[0]) __array = (array); \
190 typeof(len) __len = (len); \
191 __unqual_scalar_typeof(__array[0]) __element = __array[--__len];\
192 while (__len--) \
193 __element = op(__element, __array[__len]); \
194 __element; })
195
196/**
197 * min_array - return minimum of values present in an array
198 * @array: array
199 * @len: array length
200 *
201 * Note that @len must not be zero (empty array).
202 */
203#define min_array(array, len) __minmax_array(min, array, len)
204
205/**
206 * max_array - return maximum of values present in an array
207 * @array: array
208 * @len: array length
209 *
210 * Note that @len must not be zero (empty array).
211 */
212#define max_array(array, len) __minmax_array(max, array, len)
213
214/**
215 * clamp_t - return a value clamped to a given range using a given type
216 * @type: the type of variable to use
217 * @val: current value
218 * @lo: minimum allowable value
219 * @hi: maximum allowable value
220 *
221 * This macro does no typechecking and uses temporary variables of type
222 * @type to make all the comparisons.
223 */
224#define clamp_t(type, val, lo, hi) __careful_clamp((type)(val), (type)(lo), (type)(hi))
225
226/**
227 * clamp_val - return a value clamped to a given range using val's type
228 * @val: current value
229 * @lo: minimum allowable value
230 * @hi: maximum allowable value
231 *
232 * This macro does no typechecking and uses temporary variables of whatever
233 * type the input argument @val is. This is useful when @val is an unsigned
234 * type and @lo and @hi are literals that will otherwise be assigned a signed
235 * integer type.
236 */
237#define clamp_val(val, lo, hi) clamp_t(typeof(val), val, lo, hi)
238
239static inline bool in_range64(u64 val, u64 start, u64 len)
240{
241 return (val - start) < len;
242}
243
244static inline bool in_range32(u32 val, u32 start, u32 len)
245{
246 return (val - start) < len;
247}
248
249/**
250 * in_range - Determine if a value lies within a range.
251 * @val: Value to test.
252 * @start: First value in range.
253 * @len: Number of values in range.
254 *
255 * This is more efficient than "if (start <= val && val < (start + len))".
256 * It also gives a different answer if @start + @len overflows the size of
257 * the type by a sufficient amount to encompass @val. Decide for yourself
258 * which behaviour you want, or prove that start + len never overflow.
259 * Do not blindly replace one form with the other.
260 */
261#define in_range(val, start, len) \
262 ((sizeof(start) | sizeof(len) | sizeof(val)) <= sizeof(u32) ? \
263 in_range32(val, start, len) : in_range64(val, start, len))
264
265/**
266 * swap - swap values of @a and @b
267 * @a: first value
268 * @b: second value
269 */
270#define swap(a, b) \
271 do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
272
273#endif /* _LINUX_MINMAX_H */
274

source code of linux/include/linux/minmax.h