Function acos

include/half.hpp:3657–3672

Arc cosine function. This function is exact to rounding for all rounding modes. See also:** Documentation for [std::acos](https://en.cppreference.com/w/cpp/numeric/math/acos). \param arg function argument \return arc cosine value of \a arg \exception FE_INVALID for signaling NaN or if abs(\a arg) > 1 \exception FE_OVERFLOW, ...UNDERFLOW, ...INEXACT according to rounding

	/// \exception FE_INVALID for signaling NaN or if abs(\a arg) > 1
	/// \exception FE_OVERFLOW, ...UNDERFLOW, ...INEXACT according to rounding
	inline half acos(half arg)
	{
	#ifdef HALF_ARITHMETIC_TYPE
		return half(detail::binary, detail::float2half<half::round_style>(std::acos(detail::half2float<detail::internal_t>(arg.data_))));
	#else
		unsigned int abs = arg.data_ & 0x7FFF, sign = arg.data_ >> 15;
		if(!abs)
			return half(detail::binary, detail::rounded<half::round_style,true>(0x3E48, 0, 1));
		if(abs >= 0x3C00)
			return half(detail::binary,	(abs>0x7C00) ? detail::signal(arg.data_) : (abs>0x3C00) ? detail::invalid() :
										sign ? detail::rounded<half::round_style,true>(0x4248, 0, 1) : 0);
		std::pair<detail::uint32,detail::uint32> cs = detail::atan2_args(abs);
		detail::uint32 m = detail::atan2(cs.second, cs.first, 28);
		return half(detail::binary, detail::fixed2half<half::round_style,31,false,true,true>(sign ? (0xC90FDAA2-m) : m, 15, 0, sign));
	#endif
	}

	/// Arc tangent function.
	/// This function is exact to rounding for all rounding modes.