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249 lines
8.0 KiB
249 lines
8.0 KiB
/* SPDX-License-Identifier: GPL-2.0 OR MIT */ |
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#ifndef __LINUX_OVERFLOW_H |
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#define __LINUX_OVERFLOW_H |
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#include <linux/compiler.h> |
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#include <linux/limits.h> |
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#include <linux/const.h> |
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/* |
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* We need to compute the minimum and maximum values representable in a given |
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* type. These macros may also be useful elsewhere. It would seem more obvious |
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* to do something like: |
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* |
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* #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0) |
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* #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0) |
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* |
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* Unfortunately, the middle expressions, strictly speaking, have |
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* undefined behaviour, and at least some versions of gcc warn about |
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* the type_max expression (but not if -fsanitize=undefined is in |
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* effect; in that case, the warning is deferred to runtime...). |
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* |
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* The slightly excessive casting in type_min is to make sure the |
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* macros also produce sensible values for the exotic type _Bool. [The |
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* overflow checkers only almost work for _Bool, but that's |
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* a-feature-not-a-bug, since people shouldn't be doing arithmetic on |
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* _Bools. Besides, the gcc builtins don't allow _Bool* as third |
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* argument.] |
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* |
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* Idea stolen from |
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* https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html - |
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* credit to Christian Biere. |
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*/ |
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#define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type))) |
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#define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T))) |
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#define type_min(T) ((T)((T)-type_max(T)-(T)1)) |
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/* |
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* Avoids triggering -Wtype-limits compilation warning, |
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* while using unsigned data types to check a < 0. |
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*/ |
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#define is_non_negative(a) ((a) > 0 || (a) == 0) |
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#define is_negative(a) (!(is_non_negative(a))) |
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/* |
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* Allows for effectively applying __must_check to a macro so we can have |
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* both the type-agnostic benefits of the macros while also being able to |
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* enforce that the return value is, in fact, checked. |
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*/ |
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static inline bool __must_check __must_check_overflow(bool overflow) |
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{ |
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return unlikely(overflow); |
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} |
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/** |
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* check_add_overflow() - Calculate addition with overflow checking |
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* @a: first addend |
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* @b: second addend |
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* @d: pointer to store sum |
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* |
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* Returns 0 on success. |
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* |
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* *@d holds the results of the attempted addition, but is not considered |
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* "safe for use" on a non-zero return value, which indicates that the |
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* sum has overflowed or been truncated. |
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*/ |
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#define check_add_overflow(a, b, d) \ |
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__must_check_overflow(__builtin_add_overflow(a, b, d)) |
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/** |
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* check_sub_overflow() - Calculate subtraction with overflow checking |
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* @a: minuend; value to subtract from |
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* @b: subtrahend; value to subtract from @a |
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* @d: pointer to store difference |
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* |
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* Returns 0 on success. |
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* |
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* *@d holds the results of the attempted subtraction, but is not considered |
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* "safe for use" on a non-zero return value, which indicates that the |
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* difference has underflowed or been truncated. |
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*/ |
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#define check_sub_overflow(a, b, d) \ |
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__must_check_overflow(__builtin_sub_overflow(a, b, d)) |
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/** |
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* check_mul_overflow() - Calculate multiplication with overflow checking |
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* @a: first factor |
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* @b: second factor |
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* @d: pointer to store product |
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* |
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* Returns 0 on success. |
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* |
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* *@d holds the results of the attempted multiplication, but is not |
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* considered "safe for use" on a non-zero return value, which indicates |
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* that the product has overflowed or been truncated. |
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*/ |
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#define check_mul_overflow(a, b, d) \ |
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__must_check_overflow(__builtin_mul_overflow(a, b, d)) |
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/** |
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* check_shl_overflow() - Calculate a left-shifted value and check overflow |
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* @a: Value to be shifted |
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* @s: How many bits left to shift |
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* @d: Pointer to where to store the result |
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* |
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* Computes *@d = (@a << @s) |
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* |
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* Returns true if '*@d' cannot hold the result or when '@a << @s' doesn't |
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* make sense. Example conditions: |
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* |
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* - '@a << @s' causes bits to be lost when stored in *@d. |
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* - '@s' is garbage (e.g. negative) or so large that the result of |
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* '@a << @s' is guaranteed to be 0. |
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* - '@a' is negative. |
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* - '@a << @s' sets the sign bit, if any, in '*@d'. |
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* |
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* '*@d' will hold the results of the attempted shift, but is not |
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* considered "safe for use" if true is returned. |
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*/ |
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#define check_shl_overflow(a, s, d) __must_check_overflow(({ \ |
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typeof(a) _a = a; \ |
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typeof(s) _s = s; \ |
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typeof(d) _d = d; \ |
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u64 _a_full = _a; \ |
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unsigned int _to_shift = \ |
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is_non_negative(_s) && _s < 8 * sizeof(*d) ? _s : 0; \ |
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*_d = (_a_full << _to_shift); \ |
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(_to_shift != _s || is_negative(*_d) || is_negative(_a) || \ |
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(*_d >> _to_shift) != _a); \ |
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})) |
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/** |
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* size_mul() - Calculate size_t multiplication with saturation at SIZE_MAX |
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* @factor1: first factor |
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* @factor2: second factor |
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* |
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* Returns: calculate @factor1 * @factor2, both promoted to size_t, |
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* with any overflow causing the return value to be SIZE_MAX. The |
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* lvalue must be size_t to avoid implicit type conversion. |
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*/ |
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static inline size_t __must_check size_mul(size_t factor1, size_t factor2) |
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{ |
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size_t bytes; |
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if (check_mul_overflow(factor1, factor2, &bytes)) |
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return SIZE_MAX; |
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return bytes; |
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} |
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/** |
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* size_add() - Calculate size_t addition with saturation at SIZE_MAX |
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* @addend1: first addend |
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* @addend2: second addend |
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* |
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* Returns: calculate @addend1 + @addend2, both promoted to size_t, |
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* with any overflow causing the return value to be SIZE_MAX. The |
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* lvalue must be size_t to avoid implicit type conversion. |
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*/ |
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static inline size_t __must_check size_add(size_t addend1, size_t addend2) |
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{ |
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size_t bytes; |
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if (check_add_overflow(addend1, addend2, &bytes)) |
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return SIZE_MAX; |
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return bytes; |
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} |
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/** |
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* size_sub() - Calculate size_t subtraction with saturation at SIZE_MAX |
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* @minuend: value to subtract from |
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* @subtrahend: value to subtract from @minuend |
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* |
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* Returns: calculate @minuend - @subtrahend, both promoted to size_t, |
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* with any overflow causing the return value to be SIZE_MAX. For |
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* composition with the size_add() and size_mul() helpers, neither |
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* argument may be SIZE_MAX (or the result with be forced to SIZE_MAX). |
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* The lvalue must be size_t to avoid implicit type conversion. |
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*/ |
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static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) |
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{ |
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size_t bytes; |
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if (minuend == SIZE_MAX || subtrahend == SIZE_MAX || |
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check_sub_overflow(minuend, subtrahend, &bytes)) |
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return SIZE_MAX; |
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return bytes; |
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} |
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/** |
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* array_size() - Calculate size of 2-dimensional array. |
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* @a: dimension one |
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* @b: dimension two |
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* |
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* Calculates size of 2-dimensional array: @a * @b. |
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* |
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* Returns: number of bytes needed to represent the array or SIZE_MAX on |
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* overflow. |
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*/ |
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#define array_size(a, b) size_mul(a, b) |
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/** |
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* array3_size() - Calculate size of 3-dimensional array. |
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* @a: dimension one |
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* @b: dimension two |
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* @c: dimension three |
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* |
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* Calculates size of 3-dimensional array: @a * @b * @c. |
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* |
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* Returns: number of bytes needed to represent the array or SIZE_MAX on |
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* overflow. |
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*/ |
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#define array3_size(a, b, c) size_mul(size_mul(a, b), c) |
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/** |
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* flex_array_size() - Calculate size of a flexible array member |
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* within an enclosing structure. |
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* @p: Pointer to the structure. |
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* @member: Name of the flexible array member. |
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* @count: Number of elements in the array. |
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* |
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* Calculates size of a flexible array of @count number of @member |
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* elements, at the end of structure @p. |
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* |
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* Return: number of bytes needed or SIZE_MAX on overflow. |
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*/ |
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#define flex_array_size(p, member, count) \ |
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__builtin_choose_expr(__is_constexpr(count), \ |
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(count) * sizeof(*(p)->member) + __must_be_array((p)->member), \ |
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size_mul(count, sizeof(*(p)->member) + __must_be_array((p)->member))) |
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/** |
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* struct_size() - Calculate size of structure with trailing flexible array. |
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* @p: Pointer to the structure. |
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* @member: Name of the array member. |
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* @count: Number of elements in the array. |
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* |
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* Calculates size of memory needed for structure @p followed by an |
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* array of @count number of @member elements. |
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* |
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* Return: number of bytes needed or SIZE_MAX on overflow. |
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*/ |
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#define struct_size(p, member, count) \ |
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__builtin_choose_expr(__is_constexpr(count), \ |
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sizeof(*(p)) + flex_array_size(p, member, count), \ |
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size_add(sizeof(*(p)), flex_array_size(p, member, count))) |
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#endif /* __LINUX_OVERFLOW_H */
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