Boost uses unoptimized subtraction because of typo in intel_intrinsics.hpp

From: Neill Clift (NeillClift_at_[hidden])
Date: 2021-08-18 16:23:46

Hi,
In my program I am seeing my code use the slower (I assume) subtract_unsigned_constexpr rather than subtract_unsigned with he borrow chain handled intrinsics.
This seems to be happening because of these lines in intel_intrinsics.hpp:

#if defined(__clang__) && (__clang__ < 9)
// We appear to crash the compiler if we try to use these intrinsics?
#undef BOOST_MP_HAS_IMMINTRIN_H
#endif

__clang__ is not the version but just the value 1. I expect this should be the major version instead:

#define __clang__ 1
#define __clang_major__ 12
#define __clang_minor__ 0

As an aside 128bit support does work in windows with clang. I have to force it on like this:

#define __STRICT_ANSI__
#define BOOST_HAS_INT128
#define BOOST_MP_HAS_IMMINTRIN_H

#include <boost/multiprecision/cpp_int.hpp>

Thanks.
Neill.