1/*
2 * Copyright (c) 2015 Apple Inc. All rights reserved.
3 *
4 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
9 * compliance with the License. The rights granted to you under the License
10 * may not be used to create, or enable the creation or redistribution of,
11 * unlawful or unlicensed copies of an Apple operating system, or to
12 * circumvent, violate, or enable the circumvention or violation of, any
13 * terms of an Apple operating system software license agreement.
14 *
15 * Please obtain a copy of the License at
16 * http://www.opensource.apple.com/apsl/ and read it before using this file.
17 *
18 * The Original Code and all software distributed under the License are
19 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
20 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
21 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
22 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
23 * Please see the License for the specific language governing rights and
24 * limitations under the License.
25 *
26 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
27 */
28
29/*
30 * Facilities for performing type- and overflow-checked arithmetic. These
31 * functions return non-zero if overflow occured, zero otherwise. In either case,
32 * the potentially overflowing operation is fully performed, mod the size of the
33 * output type. See:
34 * http://clang.llvm.org/docs/LanguageExtensions.html#checked-arithmetic-builtins
35 * for full details.
36 *
37 * The compiler enforces that users of os_*_overflow() check the return value to
38 * determine whether overflow occured.
39 */
40
41#ifndef _OS_OVERFLOW_H
42#define _OS_OVERFLOW_H
43
44#include <sys/cdefs.h>
45#include <stdbool.h>
46#include <os/base.h>
47
48bool __header_always_inline OS_WARN_RESULT
49__os_warn_unused(__const bool x)
50{
51 return x;
52}
53
54#if __has_builtin(__builtin_add_overflow) && \
55 __has_builtin(__builtin_sub_overflow) && \
56 __has_builtin(__builtin_mul_overflow)
57
58#define os_add_overflow(a, b, res) __os_warn_unused(__builtin_add_overflow((a), (b), (res)))
59#define os_sub_overflow(a, b, res) __os_warn_unused(__builtin_sub_overflow((a), (b), (res)))
60#define os_mul_overflow(a, b, res) __os_warn_unused(__builtin_mul_overflow((a), (b), (res)))
61
62#else
63
64/* compile-time assertion that 'x' and 'y' are equivalent types */
65#ifdef __cplusplus
66#define __OS_TYPE_CHECK(x, y) do { \
67 __typeof__(x) _x; \
68 __typeof__(y) _y; \
69 (void)(&_x == &_y, "overflow arithmetic: incompatible types"); \
70} while (0)
71#else
72#define __OS_TYPE_CHECK(x, y) do { \
73 _Static_assert(__builtin_types_compatible_p(__typeof(x),__typeof(y)), \
74 "overflow arithmetic: incompatible types"); \
75} while (0)
76#endif
77
78#define __os_add_overflow_func(T,U,V) _Generic((T), \
79 unsigned: __builtin_uadd_overflow, \
80 unsigned long: __builtin_uaddl_overflow, \
81 unsigned long long: __builtin_uaddll_overflow, \
82 int: __builtin_sadd_overflow, \
83 long: __builtin_saddl_overflow, \
84 long long: __builtin_saddll_overflow \
85 )(T,U,V)
86
87#define __os_sub_overflow_func(T,U,V) _Generic((T), \
88 unsigned: __builtin_usub_overflow, \
89 unsigned long: __builtin_usubl_overflow, \
90 unsigned long long: __builtin_usubll_overflow, \
91 int: __builtin_ssub_overflow, \
92 long: __builtin_ssubl_overflow, \
93 long long: __builtin_ssubll_overflow \
94 )(T,U,V)
95
96#define __os_mul_overflow_func(T,U,V) _Generic((T), \
97 unsigned: __builtin_umul_overflow, \
98 unsigned long: __builtin_umull_overflow, \
99 unsigned long long: __builtin_umulll_overflow, \
100 int: __builtin_smul_overflow, \
101 long: __builtin_smull_overflow, \
102 long long: __builtin_smulll_overflow \
103 )(T,U,V)
104
105#define os_add_overflow(a, b, res) __os_warn_unused(__extension__({ \
106 __OS_TYPE_CHECK((a), (b)); \
107 __OS_TYPE_CHECK((b), *(res)); \
108 __os_add_overflow_func((a), (b), (res)); \
109}))
110
111#define os_sub_overflow(a, b, res) __os_warn_unused(__extension__({ \
112 __OS_TYPE_CHECK((a), (b)); \
113 __OS_TYPE_CHECK((b), *(res)); \
114 __os_sub_overflow_func((a), (b), (res)); \
115}))
116
117#define os_mul_overflow(a, b, res) __os_warn_unused(__extension__({ \
118 __OS_TYPE_CHECK((a), (b)); \
119 __OS_TYPE_CHECK((b), *(res)); \
120 __os_mul_overflow_func((a), (b), (res)); \
121}))
122
123#endif /* __has_builtin(...) */
124
125/* os_add3_overflow(a, b, c) -> (a + b + c) */
126#define os_add3_overflow(a, b, c, res) __os_warn_unused(__extension__({ \
127 __typeof(*(res)) _tmp; \
128 bool _s, _t; \
129 _s = os_add_overflow((a), (b), &_tmp); \
130 _t = os_add_overflow((c), _tmp, (res)); \
131 _s | _t; \
132}))
133
134/* os_mul3_overflow(a, b, c) -> (a * b * c) */
135#define os_mul3_overflow(a, b, c, res) __os_warn_unused(__extension__({ \
136 __typeof(*(res)) _tmp; \
137 bool _s, _t; \
138 _s = os_mul_overflow((a), (b), &_tmp); \
139 _t = os_mul_overflow((c), _tmp, (res)); \
140 _s | _t; \
141}))
142
143/* os_add_and_mul_overflow(a, b, x) -> (a + b)*x */
144#define os_add_and_mul_overflow(a, b, x, res) __os_warn_unused(__extension__({ \
145 __typeof(*(res)) _tmp; \
146 bool _s, _t; \
147 _s = os_add_overflow((a), (b), &_tmp); \
148 _t = os_mul_overflow((x), _tmp, (res)); \
149 _s | _t; \
150}))
151
152/* os_mul_and_add_overflow(a, x, b) -> a*x + b */
153#define os_mul_and_add_overflow(a, x, b, res) __os_warn_unused(__extension__({ \
154 __typeof(*(res)) _tmp; \
155 bool _s, _t; \
156 _s = os_mul_overflow((a), (x), &_tmp); \
157 _t = os_add_overflow((b), _tmp, (res)); \
158 _s | _t; \
159}))
160
161#define os_convert_overflow(a, res) os_add_overflow((a), 0, (res))
162
163#endif /* _OS_OVERFLOW_H */
164