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 /*
30 * __sign_use for integer expressions:
31 * bit #0 set if ok for unsigned comparisons
32 * bit #1 set if ok for signed comparisons
33 *
34 * In particular, statically non-negative signed integer
35 * expressions are ok for both.
36 *
37 * NOTE! Unsigned types smaller than 'int' are implicitly
38 * converted to 'int' in expressions, and are accepted for
39 * signed conversions for now. This is debatable.
40 *
41 * Note that 'x' is the original expression, and 'ux' is
42 * the unique variable that contains the value.
43 *
44 * We use 'ux' for pure type checking, and 'x' for when
45 * we need to look at the value (but without evaluating
46 * it for side effects! Careful to only ever evaluate it
47 * with sizeof() or __builtin_constant_p() etc).
48 *
49 * Pointers end up being checked by the normal C type
50 * rules at the actual comparison, and these expressions
51 * only need to be careful to not cause warnings for
52 * pointer use.
53 */
54 #define __signed_type_use(x,ux) (2+__is_nonneg(x,ux))
55 #define __unsigned_type_use(x,ux) (1+2*(sizeof(ux)<4))
56 #define __sign_use(x,ux) (is_signed_type(typeof(ux))? \
57 __signed_type_use(x,ux):__unsigned_type_use(x,ux))
58
59 /*
60 * To avoid warnings about casting pointers to integers
61 * of different sizes, we need that special sign type.
62 *
63 * On 64-bit we can just always use 'long', since any
64 * integer or pointer type can just be cast to that.
65 *
66 * This does not work for 128-bit signed integers since
67 * the cast would truncate them, but we do not use s128
68 * types in the kernel (we do use 'u128', but they will
69 * be handled by the !is_signed_type() case).
70 *
71 * NOTE! The cast is there only to avoid any warnings
72 * from when values that aren't signed integer types.
73 */
74 #ifdef CONFIG_64BIT
75 #define __signed_type(ux) long
76 #else
77 #define __signed_type(ux) typeof(__builtin_choose_expr(sizeof(ux)>4,1LL,1L))
78 #endif
79 #define __is_nonneg(x,ux) statically_true((__signed_type(ux))(x)>=0)
80
81 #define __types_ok(x,y,ux,uy) \
82 (__sign_use(x,ux) & __sign_use(y,uy))
83
84 #define __types_ok3(x,y,z,ux,uy,uz) \
85 (__sign_use(x,ux) & __sign_use(y,uy) & __sign_use(z,uz))
86
87 #define __cmp_op_min <
88 #define __cmp_op_max >
89
90 #define __cmp(op, x, y) ((x) __cmp_op_##op (y) ? (x) : (y))
91
92 #define __cmp_once_unique(op, type, x, y, ux, uy) \
93 ({ type ux = (x); type uy = (y); __cmp(op, ux, uy); })
94
95 #define __cmp_once(op, type, x, y) \
96 __cmp_once_unique(op, type, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
97
98 #define __careful_cmp_once(op, x, y, ux, uy) ({ \
99 __auto_type ux = (x); __auto_type uy = (y); \
100 BUILD_BUG_ON_MSG(!__types_ok(x,y,ux,uy), \
101 #op"("#x", "#y") signedness error"); \
102 __cmp(op, ux, uy); })
103
104 #define __careful_cmp(op, x, y) \
105 __careful_cmp_once(op, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
106
107 #define __clamp(val, lo, hi) \
108 ((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val)))
109
110 #define __clamp_once(val, lo, hi, uval, ulo, uhi) ({ \
111 __auto_type uval = (val); \
112 __auto_type ulo = (lo); \
113 __auto_type uhi = (hi); \
114 static_assert(__builtin_choose_expr(__is_constexpr((lo) > (hi)), \
115 (lo) <= (hi), true), \
116 "clamp() low limit " #lo " greater than high limit " #hi); \
117 BUILD_BUG_ON_MSG(!__types_ok3(val,lo,hi,uval,ulo,uhi), \
118 "clamp("#val", "#lo", "#hi") signedness error"); \
119 __clamp(uval, ulo, uhi); })
120
121 #define __careful_clamp(val, lo, hi) \
122 __clamp_once(val, lo, hi, __UNIQUE_ID(v_), __UNIQUE_ID(l_), __UNIQUE_ID(h_))
123
124 /**
125 * min - return minimum of two values of the same or compatible types
126 * @x: first value
127 * @y: second value
128 */
129 #define min(x, y) __careful_cmp(min, x, y)
130
131 /**
132 * max - return maximum of two values of the same or compatible types
133 * @x: first value
134 * @y: second value
135 */
136 #define max(x, y) __careful_cmp(max, x, y)
137
138 /**
139 * umin - return minimum of two non-negative values
140 * Signed types are zero extended to match a larger unsigned type.
141 * @x: first value
142 * @y: second value
143 */
144 #define umin(x, y) \
145 __careful_cmp(min, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
146
147 /**
148 * umax - return maximum of two non-negative values
149 * @x: first value
150 * @y: second value
151 */
152 #define umax(x, y) \
153 __careful_cmp(max, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
154
155 #define __careful_op3(op, x, y, z, ux, uy, uz) ({ \
156 __auto_type ux = (x); __auto_type uy = (y);__auto_type uz = (z);\
157 BUILD_BUG_ON_MSG(!__types_ok3(x,y,z,ux,uy,uz), \
158 #op"3("#x", "#y", "#z") signedness error"); \
159 __cmp(op, ux, __cmp(op, uy, uz)); })
160
161 /**
162 * min3 - return minimum of three values
163 * @x: first value
164 * @y: second value
165 * @z: third value
166 */
167 #define min3(x, y, z) \
168 __careful_op3(min, x, y, z, __UNIQUE_ID(x_), __UNIQUE_ID(y_), __UNIQUE_ID(z_))
169
170 /**
171 * max3 - return maximum of three values
172 * @x: first value
173 * @y: second value
174 * @z: third value
175 */
176 #define max3(x, y, z) \
177 __careful_op3(max, x, y, z, __UNIQUE_ID(x_), __UNIQUE_ID(y_), __UNIQUE_ID(z_))
178
179 /**
180 * min_not_zero - return the minimum that is _not_ zero, unless both are zero
181 * @x: value1
182 * @y: value2
183 */
184 #define min_not_zero(x, y) ({ \
185 typeof(x) __x = (x); \
186 typeof(y) __y = (y); \
187 __x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
188
189 /**
190 * clamp - return a value clamped to a given range with strict typechecking
191 * @val: current value
192 * @lo: lowest allowable value
193 * @hi: highest allowable value
194 *
195 * This macro does strict typechecking of @lo/@hi to make sure they are of the
196 * same type as @val. See the unnecessary pointer comparisons.
197 */
198 #define clamp(val, lo, hi) __careful_clamp(val, lo, hi)
199
200 /*
201 * ..and if you can't take the strict
202 * types, you can specify one yourself.
203 *
204 * Or not use min/max/clamp at all, of course.
205 */
206
207 /**
208 * min_t - return minimum of two values, using the specified type
209 * @type: data type to use
210 * @x: first value
211 * @y: second value
212 */
213 #define min_t(type, x, y) __cmp_once(min, type, x, y)
214
215 /**
216 * max_t - return maximum of two values, using the specified type
217 * @type: data type to use
218 * @x: first value
219 * @y: second value
220 */
221 #define max_t(type, x, y) __cmp_once(max, type, x, y)
222
223 /*
224 * Do not check the array parameter using __must_be_array().
225 * In the following legit use-case where the "array" passed is a simple pointer,
226 * __must_be_array() will return a failure.
227 * --- 8< ---
228 * int *buff
229 * ...
230 * min = min_array(buff, nb_items);
231 * --- 8< ---
232 *
233 * The first typeof(&(array)[0]) is needed in order to support arrays of both
234 * 'int *buff' and 'int buff[N]' types.
235 *
236 * The array can be an array of const items.
237 * typeof() keeps the const qualifier. Use __unqual_scalar_typeof() in order
238 * to discard the const qualifier for the __element variable.
239 */
240 #define __minmax_array(op, array, len) ({ \
241 typeof(&(array)[0]) __array = (array); \
242 typeof(len) __len = (len); \
243 __unqual_scalar_typeof(__array[0]) __element = __array[--__len];\
244 while (__len--) \
245 __element = op(__element, __array[__len]); \
246 __element; })
247
248 /**
249 * min_array - return minimum of values present in an array
250 * @array: array
251 * @len: array length
252 *
253 * Note that @len must not be zero (empty array).
254 */
255 #define min_array(array, len) __minmax_array(min, array, len)
256
257 /**
258 * max_array - return maximum of values present in an array
259 * @array: array
260 * @len: array length
261 *
262 * Note that @len must not be zero (empty array).
263 */
264 #define max_array(array, len) __minmax_array(max, array, len)
265
266 /**
267 * clamp_t - return a value clamped to a given range using a given type
268 * @type: the type of variable to use
269 * @val: current value
270 * @lo: minimum allowable value
271 * @hi: maximum allowable value
272 *
273 * This macro does no typechecking and uses temporary variables of type
274 * @type to make all the comparisons.
275 */
276 #define clamp_t(type, val, lo, hi) __careful_clamp((type)(val), (type)(lo), (type)(hi))
277
278 /**
279 * clamp_val - return a value clamped to a given range using val's type
280 * @val: current value
281 * @lo: minimum allowable value
282 * @hi: maximum allowable value
283 *
284 * This macro does no typechecking and uses temporary variables of whatever
285 * type the input argument @val is. This is useful when @val is an unsigned
286 * type and @lo and @hi are literals that will otherwise be assigned a signed
287 * integer type.
288 */
289 #define clamp_val(val, lo, hi) clamp_t(typeof(val), val, lo, hi)
290
291 static inline bool in_range64(u64 val, u64 start, u64 len)
292 {
293 return (val - start) < len;
294 }
295
296 static inline bool in_range32(u32 val, u32 start, u32 len)
297 {
298 return (val - start) < len;
299 }
300
301 /**
302 * in_range - Determine if a value lies within a range.
303 * @val: Value to test.
304 * @start: First value in range.
305 * @len: Number of values in range.
306 *
307 * This is more efficient than "if (start <= val && val < (start + len))".
308 * It also gives a different answer if @start + @len overflows the size of
309 * the type by a sufficient amount to encompass @val. Decide for yourself
310 * which behaviour you want, or prove that start + len never overflow.
311 * Do not blindly replace one form with the other.
312 */
313 #define in_range(val, start, len) \
314 ((sizeof(start) | sizeof(len) | sizeof(val)) <= sizeof(u32) ? \
315 in_range32(val, start, len) : in_range64(val, start, len))
316
317 /**
318 * swap - swap values of @a and @b
319 * @a: first value
320 * @b: second value
321 */
322 #define swap(a, b) \
323 do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
324
325 /*
326 * Use these carefully: no type checking, and uses the arguments
327 * multiple times. Use for obvious constants only.
328 */
329 #define MIN(a,b) __cmp(min,a,b)
330 #define MAX(a,b) __cmp(max,a,b)
331 #define MIN_T(type,a,b) __cmp(min,(type)(a),(type)(b))
332 #define MAX_T(type,a,b) __cmp(max,(type)(a),(type)(b))
333
334 #endif /* _LINUX_MINMAX_H */
335
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