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+/*-
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+ * Copyright (c) 2018 Taylor R. Campbell
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+ * All rights reserved.
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+ *
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+ * Redistribution and use in source and binary forms, with or without
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+ * modification, are permitted provided that the following conditions
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+ * are met:
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+ * 1. Redistributions of source code must retain the above copyright
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+ * notice, this list of conditions and the following disclaimer.
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+ * 2. Redistributions in binary form must reproduce the above copyright
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+ * notice, this list of conditions and the following disclaimer in the
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+ * documentation and/or other materials provided with the distribution.
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+ *
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+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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+ * SUCH DAMAGE.
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+ */
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+
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+/**
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+ * \file ctassert.h
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+ *
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+ * \brief Compile-time assertions: CTASSERT(expression).
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+ */
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+
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+#ifndef TOR_CTASSERT_H
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+#define TOR_CTASSERT_H
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+
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+#include "lib/cc/compat_compiler.h"
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+
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+/**
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+ * CTASSERT(expression)
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+ *
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+ * Trigger a compiler error if expression is false.
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+ */
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+#if __STDC_VERSION__ >= 201112L
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+
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+/* If C11 is available, just use _Static_assert. */
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+#define CTASSERT(x) _Static_assert(x, #x)
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+
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+#else
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+
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+/*
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+ * If C11 is not available, expand __COUNTER__, or __INCLUDE_LEVEL__
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+ * and __LINE__, or just __LINE__, with an intermediate preprocessor
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+ * macro CTASSERT_EXPN, and then use CTASSERT_DECL to paste the
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+ * expansions together into a unique name.
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+ *
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+ * We use this name as a typedef of an array type with a positive
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+ * length if the assertion is true, and a negative length of the
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+ * assertion is false, which is invalid and hence triggers a compiler
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+ * error.
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+ */
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+#if defined(__COUNTER__)
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+#define CTASSERT(x) CTASSERT_EXPN(x, c, __COUNTER__)
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+#elif defined(__INCLUDE_LEVEL__)
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+#define CTASSERT(x) CTASSERT_EXPN(x, __INCLUDE_LEVEL__, __LINE__)
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+#else
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+#define CTASSERT(x) CTASSERT_EXPN(x, l, __LINE__) /* hope it's unique enough */
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+#endif
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+
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+#define CTASSERT_EXPN(x, a, b) CTASSERT_DECL(x, a, b)
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+#define CTASSERT_DECL(x, a, b) \
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+ typedef char tor_ctassert_##a##_##b[(x) ? 1 : -1] ATTR_UNUSED
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+
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+#endif
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+
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+#endif /* !defined(TOR_CTASSERT_H) */
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Taylor R Campbell