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