/usr/include/isc/likely.h is in libbind-dev 1:9.11.3+dfsg-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | /*
 * Copyright (C) 2017  Internet Systems Consortium, Inc. ("ISC")
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
#ifndef ISC_LIKELY_H
#define ISC_LIKELY_H 1
/*%
 * Performance
 */
#ifdef HAVE_BUILTIN_EXPECT
#define ISC_LIKELY(x)            __builtin_expect(!!(x), 1)
#define ISC_UNLIKELY(x)          __builtin_expect(!!(x), 0)
#else
#define ISC_LIKELY(x)            (x)
#define ISC_UNLIKELY(x)          (x)
#endif
#endif /* ISC_LIKELY_H */
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