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 several things: 12 * 13 * - Avoid multiple evaluations of the arguments (so side-effects like 14 * "x++" happen only once) when non-constant. 15 * - Perform signed v unsigned type-checking (to generate compile 16 * errors instead of nasty runtime surprises). 17 * - Unsigned char/short are always promoted to signed int and can be 18 * compared against signed or unsigned arguments. 19 * - Unsigned arguments can be compared against non-negative signed constants. 20 * - Comparison of a signed argument against an unsigned constant fails 21 * even if the constant is below __INT_MAX__ and could be cast to int. 22 */ 23 #define __typecheck(x, y) \ 24 (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1))) 25 26 /* 27 * __sign_use for integer expressions: 28 * bit #0 set if ok for unsigned comparisons 29 * bit #1 set if ok for signed comparisons 30 * 31 * In particular, statically non-negative signed integer expressions 32 * are ok for both. 33 * 34 * NOTE! Unsigned types smaller than 'int' are implicitly converted to 'int' 35 * in expressions, and are accepted for signed conversions for now. 36 * This is debatable. 37 * 38 * Note that 'x' is the original expression, and 'ux' is the unique variable 39 * that contains the value. 40 * 41 * We use 'ux' for pure type checking, and 'x' for when we need to look at the 42 * value (but without evaluating it for side effects! 43 * Careful to only ever evaluate it with sizeof() or __builtin_constant_p() etc). 44 * 45 * Pointers end up being checked by the normal C type rules at the actual 46 * comparison, and these expressions only need to be careful to not cause 47 * warnings for pointer use. 48 */ 49 #define __sign_use(ux) (is_signed_type(typeof(ux)) ? \ 50 (2 + __is_nonneg(ux)) : (1 + 2 * (sizeof(ux) < 4))) 51 52 /* 53 * Check whether a signed value is always non-negative. 54 * 55 * A cast is needed to avoid any warnings from values that aren't signed 56 * integer types (in which case the result doesn't matter). 57 * 58 * On 64-bit any integer or pointer type can safely be cast to 'long long'. 59 * But on 32-bit we need to avoid warnings about casting pointers to integers 60 * of different sizes without truncating 64-bit values so 'long' or 'long long' 61 * must be used depending on the size of the value. 62 * 63 * This does not work for 128-bit signed integers since the cast would truncate 64 * them, but we do not use s128 types in the kernel (we do use 'u128', 65 * but they are handled by the !is_signed_type() case). 66 */ 67 #if __SIZEOF_POINTER__ == __SIZEOF_LONG_LONG__ 68 #define __is_nonneg(ux) statically_true((long long)(ux) >= 0) 69 #else 70 #define __is_nonneg(ux) statically_true( \ 71 (typeof(__builtin_choose_expr(sizeof(ux) > 4, 1LL, 1L)))(ux) >= 0) 72 #endif 73 74 #define __types_ok(ux, uy) \ 75 (__sign_use(ux) & __sign_use(uy)) 76 77 #define __types_ok3(ux, uy, uz) \ 78 (__sign_use(ux) & __sign_use(uy) & __sign_use(uz)) 79 80 #define __cmp_op_min < 81 #define __cmp_op_max > 82 83 #define __cmp(op, x, y) ((x) __cmp_op_##op (y) ? (x) : (y)) 84 85 #define __cmp_once_unique(op, type, x, y, ux, uy) \ 86 ({ type ux = (x); type uy = (y); __cmp(op, ux, uy); }) 87 88 #define __cmp_once(op, type, x, y) \ 89 __cmp_once_unique(op, type, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_)) 90 91 #define __careful_cmp_once(op, x, y, ux, uy) ({ \ 92 __auto_type ux = (x); __auto_type uy = (y); \ 93 BUILD_BUG_ON_MSG(!__types_ok(ux, uy), \ 94 #op"("#x", "#y") signedness error"); \ 95 __cmp(op, ux, uy); }) 96 97 #define __careful_cmp(op, x, y) \ 98 __careful_cmp_once(op, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_)) 99 100 /** 101 * min - return minimum of two values of the same or compatible types 102 * @x: first value 103 * @y: second value 104 */ 105 #define min(x, y) __careful_cmp(min, x, y) 106 107 /** 108 * max - return maximum of two values of the same or compatible types 109 * @x: first value 110 * @y: second value 111 */ 112 #define max(x, y) __careful_cmp(max, x, y) 113 114 /** 115 * umin - return minimum of two non-negative values 116 * Signed types are zero extended to match a larger unsigned type. 117 * @x: first value 118 * @y: second value 119 */ 120 #define umin(x, y) \ 121 __careful_cmp(min, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull) 122 123 /** 124 * umax - return maximum of two non-negative values 125 * @x: first value 126 * @y: second value 127 */ 128 #define umax(x, y) \ 129 __careful_cmp(max, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull) 130 131 #define __careful_op3(op, x, y, z, ux, uy, uz) ({ \ 132 __auto_type ux = (x); __auto_type uy = (y);__auto_type uz = (z);\ 133 BUILD_BUG_ON_MSG(!__types_ok3(ux, uy, uz), \ 134 #op"3("#x", "#y", "#z") signedness error"); \ 135 __cmp(op, ux, __cmp(op, uy, uz)); }) 136 137 /** 138 * min3 - return minimum of three values 139 * @x: first value 140 * @y: second value 141 * @z: third value 142 */ 143 #define min3(x, y, z) \ 144 __careful_op3(min, x, y, z, __UNIQUE_ID(x_), __UNIQUE_ID(y_), __UNIQUE_ID(z_)) 145 146 /** 147 * max3 - return maximum of three values 148 * @x: first value 149 * @y: second value 150 * @z: third value 151 */ 152 #define max3(x, y, z) \ 153 __careful_op3(max, x, y, z, __UNIQUE_ID(x_), __UNIQUE_ID(y_), __UNIQUE_ID(z_)) 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) __cmp_once(min, type, x, 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) __cmp_once(max, type, x, y) 170 171 /** 172 * min_not_zero - return the minimum that is _not_ zero, unless both are zero 173 * @x: value1 174 * @y: value2 175 */ 176 #define min_not_zero(x, y) ({ \ 177 typeof(x) __x = (x); \ 178 typeof(y) __y = (y); \ 179 __x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); }) 180 181 #define __clamp(val, lo, hi) \ 182 ((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val))) 183 184 #define __clamp_once(type, val, lo, hi, uval, ulo, uhi) ({ \ 185 type uval = (val); \ 186 type ulo = (lo); \ 187 type uhi = (hi); \ 188 BUILD_BUG_ON_MSG(statically_true(ulo > uhi), \ 189 "clamp() low limit " #lo " greater than high limit " #hi); \ 190 BUILD_BUG_ON_MSG(!__types_ok3(uval, ulo, uhi), \ 191 "clamp("#val", "#lo", "#hi") signedness error"); \ 192 __clamp(uval, ulo, uhi); }) 193 194 #define __careful_clamp(type, val, lo, hi) \ 195 __clamp_once(type, val, lo, hi, __UNIQUE_ID(v_), __UNIQUE_ID(l_), __UNIQUE_ID(h_)) 196 197 /** 198 * clamp - return a value clamped to a given range with typechecking 199 * @val: current value 200 * @lo: lowest allowable value 201 * @hi: highest allowable value 202 * 203 * This macro checks @val/@lo/@hi to make sure they have compatible 204 * signedness. 205 */ 206 #define clamp(val, lo, hi) __careful_clamp(__auto_type, val, lo, hi) 207 208 /** 209 * clamp_t - return a value clamped to a given range using a given type 210 * @type: the type of variable to use 211 * @val: current value 212 * @lo: minimum allowable value 213 * @hi: maximum allowable value 214 * 215 * This macro does no typechecking and uses temporary variables of type 216 * @type to make all the comparisons. 217 */ 218 #define clamp_t(type, val, lo, hi) __careful_clamp(type, val, lo, hi) 219 220 /** 221 * clamp_val - return a value clamped to a given range using val's type 222 * @val: current value 223 * @lo: minimum allowable value 224 * @hi: maximum allowable value 225 * 226 * This macro does no typechecking and uses temporary variables of whatever 227 * type the input argument @val is. This is useful when @val is an unsigned 228 * type and @lo and @hi are literals that will otherwise be assigned a signed 229 * integer type. 230 */ 231 #define clamp_val(val, lo, hi) __careful_clamp(typeof(val), val, lo, hi) 232 233 /* 234 * Do not check the array parameter using __must_be_array(). 235 * In the following legit use-case where the "array" passed is a simple pointer, 236 * __must_be_array() will return a failure. 237 * --- 8< --- 238 * int *buff 239 * ... 240 * min = min_array(buff, nb_items); 241 * --- 8< --- 242 * 243 * The first typeof(&(array)[0]) is needed in order to support arrays of both 244 * 'int *buff' and 'int buff[N]' types. 245 * 246 * The array can be an array of const items. 247 * typeof() keeps the const qualifier. Use __unqual_scalar_typeof() in order 248 * to discard the const qualifier for the __element variable. 249 */ 250 #define __minmax_array(op, array, len) ({ \ 251 typeof(&(array)[0]) __array = (array); \ 252 typeof(len) __len = (len); \ 253 __unqual_scalar_typeof(__array[0]) __element = __array[--__len];\ 254 while (__len--) \ 255 __element = op(__element, __array[__len]); \ 256 __element; }) 257 258 /** 259 * min_array - return minimum of values present in an array 260 * @array: array 261 * @len: array length 262 * 263 * Note that @len must not be zero (empty array). 264 */ 265 #define min_array(array, len) __minmax_array(min, array, len) 266 267 /** 268 * max_array - return maximum of values present in an array 269 * @array: array 270 * @len: array length 271 * 272 * Note that @len must not be zero (empty array). 273 */ 274 #define max_array(array, len) __minmax_array(max, array, len) 275 in_range64(u64 val,u64 start,u64 len)276 static inline bool in_range64(u64 val, u64 start, u64 len) 277 { 278 return (val - start) < len; 279 } 280 in_range32(u32 val,u32 start,u32 len)281 static inline bool in_range32(u32 val, u32 start, u32 len) 282 { 283 return (val - start) < len; 284 } 285 286 /** 287 * in_range - Determine if a value lies within a range. 288 * @val: Value to test. 289 * @start: First value in range. 290 * @len: Number of values in range. 291 * 292 * This is more efficient than "if (start <= val && val < (start + len))". 293 * It also gives a different answer if @start + @len overflows the size of 294 * the type by a sufficient amount to encompass @val. Decide for yourself 295 * which behaviour you want, or prove that start + len never overflow. 296 * Do not blindly replace one form with the other. 297 */ 298 #define in_range(val, start, len) \ 299 ((sizeof(start) | sizeof(len) | sizeof(val)) <= sizeof(u32) ? \ 300 in_range32(val, start, len) : in_range64(val, start, len)) 301 302 /** 303 * swap - swap values of @a and @b 304 * @a: first value 305 * @b: second value 306 */ 307 #define swap(a, b) \ 308 do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0) 309 310 /* 311 * Use these carefully: no type checking, and uses the arguments 312 * multiple times. Use for obvious constants only. 313 */ 314 #define MIN(a, b) __cmp(min, a, b) 315 #define MAX(a, b) __cmp(max, a, b) 316 #define MIN_T(type, a, b) __cmp(min, (type)(a), (type)(b)) 317 #define MAX_T(type, a, b) __cmp(max, (type)(a), (type)(b)) 318 319 #endif /* _LINUX_MINMAX_H */ 320