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 in_range64(u64 val,u64 start,u64 len)291 static inline bool in_range64(u64 val, u64 start, u64 len) 292 { 293 return (val - start) < len; 294 } 295 in_range32(u32 val,u32 start,u32 len)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