On 18/08/2021 17:23, Neill Clift via Boost-users wrote:

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:

Good catch, see https://github.com/boostorg/multiprecision/pull/356

#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>

I'll look at that separately, thanks John. -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus