/usr/include/clc/math/mad.inc is in libclc-dev 0.2.0+git20180312-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 | _CLC_OVERLOAD _CLC_DECL __CLC_GENTYPE mad(__CLC_GENTYPE a, __CLC_GENTYPE b, __CLC_GENTYPE c);
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