libkern/os/overflow.h

   1 /*
   2  * Copyright (c) 2015-2018 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
  48 bool __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 # error os_overflow expects type-generic builtins
  64 #endif /* __has_builtin(...) */
  65
  66 /* os_add3_overflow(a, b, c) -> (a + b + c) */
  67 #define os_add3_overflow(a, b, c, res) __os_warn_unused(__extension__({ \
  68         __typeof(*(res)) _tmp; \
  69         bool _s, _t; \
  70         _s = os_add_overflow((a), (b), &_tmp); \
  71         _t = os_add_overflow((c), _tmp, (res)); \
  72         _s | _t; \
  73 }))
  74
  75 /* os_mul3_overflow(a, b, c) -> (a * b * c) */
  76 #define os_mul3_overflow(a, b, c, res) __os_warn_unused(__extension__({ \
  77         __typeof(*(res)) _tmp; \
  78         bool _s, _t; \
  79         _s = os_mul_overflow((a), (b), &_tmp); \
  80         _t = os_mul_overflow((c), _tmp, (res)); \
  81         _s | _t; \
  82 }))
  83
  84 /* os_add_and_mul_overflow(a, b, x) -> (a + b)*x */
  85 #define os_add_and_mul_overflow(a, b, x, res) __os_warn_unused(__extension__({ \
  86         __typeof(*(res)) _tmp; \
  87         bool _s, _t; \
  88         _s = os_add_overflow((a), (b), &_tmp); \
  89         _t = os_mul_overflow((x), _tmp, (res)); \
  90         _s | _t; \
  91 }))
  92
  93 /* os_mul_and_add_overflow(a, x, b) -> a*x + b */
  94 #define os_mul_and_add_overflow(a, x, b, res) __os_warn_unused(__extension__({ \
  95         __typeof(*(res)) _tmp; \
  96         bool _s, _t; \
  97         _s = os_mul_overflow((a), (x), &_tmp); \
  98         _t = os_add_overflow((b), _tmp, (res)); \
  99         _s | _t; \
 100 }))
 101
 102 /* os_convert_overflow(a) -> a [converted to the result type] */
 103 #define os_convert_overflow(a, res) os_add_overflow((a), 0, (res))
 104
 105 /* os_inc_overflow(res) -> *res += 1 */
 106 #define os_inc_overflow(res) __os_warn_unused(__extension__({ \
 107         __typeof((res)) _tmp = (res); \
 108         os_add_overflow(*_tmp, 1, _tmp); \
 109 }))
 110
 111 /* os_dec_overflow(res) -> *res -= 1 */
 112 #define os_dec_overflow(res) __os_warn_unused(__extension__({ \
 113         __typeof((res)) _tmp = (res); \
 114         os_sub_overflow(*_tmp, 1, _tmp); \
 115 }))
 116
 117
 118 #endif /* _OS_OVERFLOW_H */