include/linux/minmax.h

   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 */