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	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) -> ax + 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 */