xnu-3248.40.184.tar.gz

[apple/xnu.git] / libkern / os / overflow.h

diff --git a/libkern/os/overflow.h b/libkern/os/overflow.h
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+/*
+ * Copyright (c) 2015 Apple Inc. All rights reserved.
+ *
+ * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
+ *
+ * This file contains Original Code and/or Modifications of Original Code
+ * as defined in and that are subject to the Apple Public Source License
+ * Version 2.0 (the 'License'). You may not use this file except in
+ * compliance with the License. The rights granted to you under the License
+ * may not be used to create, or enable the creation or redistribution of,
+ * unlawful or unlicensed copies of an Apple operating system, or to
+ * circumvent, violate, or enable the circumvention or violation of, any
+ * terms of an Apple operating system software license agreement.
+ *
+ * Please obtain a copy of the License at
+ * http://www.opensource.apple.com/apsl/ and read it before using this file.
+ *
+ * The Original Code and all software distributed under the License are
+ * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
+ * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
+ * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
+ * Please see the License for the specific language governing rights and
+ * limitations under the License.
+ *
+ * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
+ */
+
+/*
+ * Facilities for performing type- and overflow-checked arithmetic. These
+ * functions return non-zero if overflow occured, zero otherwise. In either case,
+ * the potentially overflowing operation is fully performed, mod the size of the
+ * output type. See:
+ * http://clang.llvm.org/docs/LanguageExtensions.html#checked-arithmetic-builtins
+ * for full details.
+ *
+ * The compiler enforces that users of os_*_overflow() check the return value to
+ * determine whether overflow occured.
+ */
+
+#ifndef _OS_OVERFLOW_H
+#define _OS_OVERFLOW_H
+
+#include <sys/cdefs.h>
+
+/* compile-time assertion that 'x' and 'y' are equivalent types */
+#define __OS_TYPE_CHECK(x, y) do { \
+       _Static_assert(__builtin_types_compatible_p(typeof(x),typeof(y)), \
+                       "overflow arithmetic: incompatible types"); \
+} while (0)
+
+#define __os_add_overflow_func(T,U,V) _Generic((T), \
+               unsigned:           __builtin_uadd_overflow, \
+               unsigned long:      __builtin_uaddl_overflow, \
+               unsigned long long: __builtin_uaddll_overflow, \
+               int:                __builtin_sadd_overflow, \
+               long:               __builtin_saddl_overflow, \
+               long long:          __builtin_saddll_overflow \
+       )(T,U,V)
+
+#define __os_sub_overflow_func(T,U,V) _Generic((T), \
+               unsigned:           __builtin_usub_overflow, \
+               unsigned long:      __builtin_usubl_overflow, \
+               unsigned long long: __builtin_usubll_overflow, \
+               int:                __builtin_ssub_overflow, \
+               long:               __builtin_ssubl_overflow, \
+               long long:          __builtin_ssubll_overflow \
+       )(T,U,V)
+
+#define __os_mul_overflow_func(T,U,V) _Generic((T), \
+               unsigned:           __builtin_umul_overflow, \
+               unsigned long:      __builtin_umull_overflow, \
+               unsigned long long: __builtin_umulll_overflow, \
+               int:                __builtin_smul_overflow, \
+               long:               __builtin_smull_overflow, \
+               long long:          __builtin_smulll_overflow \
+       )(T,U,V)
+
+int __header_always_inline __attribute__((__warn_unused_result__))
+__os_warn_unused(const int x)
+{
+       return x;
+}
+
+#define os_add_overflow(a, b, res) __os_warn_unused(({ \
+       __OS_TYPE_CHECK((a), (b)); \
+       __OS_TYPE_CHECK((b), *(res)); \
+       __os_add_overflow_func((a), (b), (res)); \
+}))
+
+#define os_add3_overflow(a, b, c, res) __os_warn_unused(({ \
+       typeof(a) _tmp; \
+       int _s, _t; \
+       _s = os_add_overflow((a), (b), &_tmp); \
+       _t = os_add_overflow((c), _tmp, (res)); \
+       _s | _t; \
+}))
+
+#define os_sub_overflow(a, b, res) __os_warn_unused(({ \
+       __OS_TYPE_CHECK((a), (b)); \
+       __OS_TYPE_CHECK((b), *(res)); \
+       __os_sub_overflow_func((a), (b), (res)); \
+}))
+
+#define os_mul_overflow(a, b, res) __os_warn_unused(({ \
+       __OS_TYPE_CHECK((a), (b)); \
+       __OS_TYPE_CHECK((b), *(res)); \
+       __os_mul_overflow_func((a), (b), (res)); \
+}))
+
+#endif /* _OS_OVERFLOW_H */