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/* nbdkit
* Copyright Red Hat
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* * Neither the name of Red Hat nor the names of its contributors may be
* used to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
* PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/* This header file defines macros and functions for checking overflow in
* common integer arithmetic operations.
*
* The macros use:
* - the "statement expression" GCC extension,
* - the "typeof" GCC extension,
* - the __builtin_add_overflow() and __builtin_mul_overflow() GCC/Clang
* built-ins.
*
* If either built-in is unavailable, the corresponding macro replaces it with
* a call to an inline C function.
*/
#ifndef NBDKIT_CHECKED_OVERFLOW_H
#define NBDKIT_CHECKED_OVERFLOW_H
#if !defined (__GNUC__) && !defined (__clang__)
#error "this file may need to be ported to your compiler"
#endif
#include <stdbool.h>
#include <stdint.h>
#include "static-assert.h"
#include "unique-name.h"
/* Add "a" and "b", both of (possibly different) unsigned integer types, and
* store the sum in "*r", which must also have some unsigned integer type.
*
* Each macro argument is evaluated exactly once, as long as it does not have
* variably modified type.
*
* The macro evaluates to "false" if "*r" can represent the mathematical sum.
* Otherwise, the macro evaluates to "true", and the low order bits of the
* mathematical sum are stored to "*r".
*/
#if HAVE_DECL___BUILTIN_ADD_OVERFLOW
#define ADD_OVERFLOW(a, b, r) ADD_OVERFLOW_BUILTIN ((a), (b), (r))
#else
#define ADD_OVERFLOW(a, b, r) ADD_OVERFLOW_FALLBACK ((a), (b), (r))
#endif
/* Multiply "a" and "b", both of (possibly different) unsigned integer types,
* and store the product in "*r", which must also have some unsigned integer
* type.
*
* Each macro argument is evaluated exactly once, as long as it does not have
* variably modified type.
*
* The macro evaluates to "false" if "*r" can represent the mathematical
* product. Otherwise, the macro evaluates to "true", and the low order bits of
* the mathematical product are stored to "*r".
*/
#if HAVE_DECL___BUILTIN_MUL_OVERFLOW
#define MUL_OVERFLOW(a, b, r) MUL_OVERFLOW_BUILTIN ((a), (b), (r))
#else
#define MUL_OVERFLOW(a, b, r) MUL_OVERFLOW_FALLBACK ((a), (b), (r))
#endif
/* The ADD_OVERFLOW_BUILTIN and MUL_OVERFLOW_BUILTIN function-like macros
* enforce the unsignedness of all their operands even though the underlying
* compiler built-ins, __builtin_add_overflow() and __builtin_mul_overflow(),
* don't depend on that. The explanation is that the fallback implementation
* does depend on the unsignedness of all operands, and the codebase should
* seamlessly build regardless of the built-in vs. fallback choice.
*
* Each macro argument is evaluated exactly once, as long as it does not have
* variably modified type.
*/
#if HAVE_DECL___BUILTIN_ADD_OVERFLOW
#define ADD_OVERFLOW_BUILTIN(a, b, r) \
({ \
STATIC_ASSERT_UNSIGNED_INT (a); \
STATIC_ASSERT_UNSIGNED_INT (b); \
STATIC_ASSERT_UNSIGNED_INT (*(r)); \
__builtin_add_overflow ((a), (b), (r)); \
})
#endif
#if HAVE_DECL___BUILTIN_MUL_OVERFLOW
#define MUL_OVERFLOW_BUILTIN(a, b, r) \
({ \
STATIC_ASSERT_UNSIGNED_INT (a); \
STATIC_ASSERT_UNSIGNED_INT (b); \
STATIC_ASSERT_UNSIGNED_INT (*(r)); \
__builtin_mul_overflow ((a), (b), (r)); \
})
#endif
/* The fallback macros call inline C functions. The unsignedness of all
* operands is enforced in order to keep the conversion to uintmax_t
* value-preserving, and to keep the conversion back from uintmax_t independent
* of the C language implementation.
*
* Each macro argument is evaluated exactly once, as long as it does not have
* variably modified type.
*
* The fallback macros and the inline C functions are defined regardless of
* HAVE_DECL___BUILTIN_ADD_OVERFLOW and HAVE_DECL___BUILTIN_MUL_OVERFLOW so
* that the test suite can always test the fallback.
*/
#define ADD_OVERFLOW_FALLBACK(a, b, r) \
ADD_OVERFLOW_FALLBACK_1 ((a), (b), (r), \
NBDKIT_UNIQUE_NAME (_overflow), \
NBDKIT_UNIQUE_NAME (_tmp))
#define ADD_OVERFLOW_FALLBACK_1(a, b, r, overflow, tmp) \
({ \
bool overflow; \
uintmax_t tmp; \
\
STATIC_ASSERT_UNSIGNED_INT (a); \
STATIC_ASSERT_UNSIGNED_INT (b); \
STATIC_ASSERT_UNSIGNED_INT (*(r)); \
overflow = check_add_overflow ((a), (b), \
(typeof (*(r)))-1, \
&tmp); \
*(r) = tmp; \
overflow; \
})
#define MUL_OVERFLOW_FALLBACK(a, b, r) \
MUL_OVERFLOW_FALLBACK_1 ((a), (b), (r), \
NBDKIT_UNIQUE_NAME (_overflow), \
NBDKIT_UNIQUE_NAME (_tmp))
#define MUL_OVERFLOW_FALLBACK_1(a, b, r, overflow, tmp) \
({ \
bool overflow; \
uintmax_t tmp; \
\
STATIC_ASSERT_UNSIGNED_INT (a); \
STATIC_ASSERT_UNSIGNED_INT (b); \
STATIC_ASSERT_UNSIGNED_INT (*(r)); \
overflow = check_mul_overflow ((a), (b), \
(typeof (*(r)))-1, \
&tmp); \
*(r) = tmp; \
overflow; \
})
/* Assert, at compile time, that the expression "x" has some unsigned integer
* type.
*
* The expression "x" is not evaluated, unless it has variably modified type.
*/
#define STATIC_ASSERT_UNSIGNED_INT(x) \
STATIC_ASSERT ((typeof (x))-1 > 0, _x_has_uint_type)
/* Assign the sum "a + b" to "*r", using uintmax_t modular arithmetic.
*
* Return true iff the addition overflows or the result exceeds "max".
*/
static inline bool
check_add_overflow (uintmax_t a, uintmax_t b, uintmax_t max, uintmax_t *r)
{
bool in_range;
*r = a + b;
in_range = a <= UINTMAX_MAX - b && *r <= max;
return !in_range;
}
/* Assign the product "a * b" to "*r", using uintmax_t modular arithmetic.
*
* Return true iff the multiplication overflows or the result exceeds "max".
*/
static inline bool
check_mul_overflow (uintmax_t a, uintmax_t b, uintmax_t max, uintmax_t *r)
{
bool in_range;
*r = a * b;
in_range = b == 0 || (a <= UINTMAX_MAX / b && *r <= max);
return !in_range;
}
#endif /* NBDKIT_CHECKED_OVERFLOW_H */
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