Test and fix mixed precision arithmetic with component types.

include/boost/multiprecision/detail/no_et_ops.hpp

@@ -52,7 +52,7 @@ namespace boost {
       BOOST_MP_FORCEINLINE BOOST_MP_CXX14_CONSTEXPR typename std::enable_if<is_compatible_arithmetic_type<V, number<B, et_off> >::value, number<B, et_off> >::type
          operator+(const number<B, et_off>& a, const V& b)
       {
-         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(a);
+         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(a, b);
          number<B, et_off>                                                    result;
          using default_ops::eval_add;
          eval_add(result.backend(), a.backend(), number<B, et_off>::canonical_value(b));
@@ -62,7 +62,7 @@ namespace boost {
       BOOST_MP_FORCEINLINE BOOST_MP_CXX14_CONSTEXPR typename std::enable_if<is_compatible_arithmetic_type<V, number<B, et_off> >::value && !is_equivalent_number_type<V, B>::value, number<B, et_off> >::type
          operator+(const V& a, const number<B, et_off>& b)
       {
-         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(b);
+         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(b, a);
          number<B, et_off>                                                    result;
          using default_ops::eval_add;
          eval_add(result.backend(), b.backend(), number<B, et_off>::canonical_value(a));
@@ -84,7 +84,7 @@ namespace boost {
       BOOST_MP_FORCEINLINE BOOST_MP_CXX14_CONSTEXPR typename std::enable_if<is_compatible_arithmetic_type<V, number<B, et_off> >::value, number<B, et_off> >::type
          operator-(const number<B, et_off>& a, const V& b)
       {
-         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(a);
+         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(a, b);
          number<B, et_off>                                                    result;
          using default_ops::eval_subtract;
          eval_subtract(result.backend(), a.backend(), number<B, et_off>::canonical_value(b));
@@ -94,7 +94,7 @@ namespace boost {
       BOOST_MP_FORCEINLINE BOOST_MP_CXX14_CONSTEXPR typename std::enable_if<is_compatible_arithmetic_type<V, number<B, et_off> >::value && !is_equivalent_number_type<V, B>::value, number<B, et_off> >::type
          operator-(const V& a, const number<B, et_off>& b)
       {
-         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(b);
+         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(b, a);
          number<B, et_off>                                                    result;
          using default_ops::eval_subtract;
          eval_subtract(result.backend(), number<B, et_off>::canonical_value(a), b.backend());
@@ -116,7 +116,7 @@ namespace boost {
       BOOST_MP_FORCEINLINE BOOST_MP_CXX14_CONSTEXPR typename std::enable_if<is_compatible_arithmetic_type<V, number<B, et_off> >::value, number<B, et_off> >::type
          operator*(const number<B, et_off>& a, const V& b)
       {
-         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(a);
+         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(a, b);
          number<B, et_off>                                                    result;
          using default_ops::eval_multiply;
          eval_multiply(result.backend(), a.backend(), number<B, et_off>::canonical_value(b));
@@ -126,7 +126,7 @@ namespace boost {
       BOOST_MP_FORCEINLINE BOOST_MP_CXX14_CONSTEXPR typename std::enable_if<is_compatible_arithmetic_type<V, number<B, et_off> >::value && !is_equivalent_number_type<V, B>::value, number<B, et_off> >::type
          operator*(const V& a, const number<B, et_off>& b)
       {
-         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(b);
+         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(b, a);
          number<B, et_off>                                                    result;
          using default_ops::eval_multiply;
          eval_multiply(result.backend(), b.backend(), number<B, et_off>::canonical_value(a));
@@ -148,7 +148,7 @@ namespace boost {
       BOOST_MP_FORCEINLINE BOOST_MP_CXX14_CONSTEXPR typename std::enable_if<is_compatible_arithmetic_type<V, number<B, et_off> >::value, number<B, et_off> >::type
          operator/(const number<B, et_off>& a, const V& b)
       {
-         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(a);
+         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(a, b);
          number<B, et_off>                                                    result;
          using default_ops::eval_divide;
          eval_divide(result.backend(), a.backend(), number<B, et_off>::canonical_value(b));
@@ -158,7 +158,7 @@ namespace boost {
       BOOST_MP_FORCEINLINE BOOST_MP_CXX14_CONSTEXPR typename std::enable_if<is_compatible_arithmetic_type<V, number<B, et_off> >::value && !is_equivalent_number_type<V, B>::value, number<B, et_off> >::type
          operator/(const V& a, const number<B, et_off>& b)
       {
-         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(b);
+         detail::scoped_default_precision<multiprecision::number<B, et_off> > precision_guard(b, a);
          number<B, et_off>                                                    result;
          using default_ops::eval_divide;
          eval_divide(result.backend(), number<B, et_off>::canonical_value(a), b.backend());

include/boost/multiprecision/detail/precision.hpp

@@ -197,6 +197,20 @@ inline BOOST_MP_CXX14_CONSTEXPR void maybe_promote_precision(T* obj)
 #define BOOST_MP_CONSTEXPR_IF_VARIABLE_PRECISION(T) if (boost::multiprecision::detail::is_variable_precision<T>::value)
 #endif
 
+template <class T>
+struct scoped_target_precision
+{
+   variable_precision_options opts;
+   scoped_target_precision() : opts(T::thread_default_variable_precision_options())
+   {
+      T::thread_default_variable_precision_options(variable_precision_options::preserve_target_precision, variable_precision_options::precision_group);
+   }
+   ~scoped_target_precision()
+   {
+      T::thread_default_variable_precision_options(opts);
+   }
+};
+
 }
 }
 } // namespace boost::multiprecision::detail

include/boost/multiprecision/mpc.hpp

@@ -562,7 +562,7 @@ struct mpc_complex_backend<0> : public detail::mpc_complex_imp<0>
    }
    template <unsigned D>
    mpc_complex_backend(const mpfr_float_backend<D>& val)
-       : detail::mpc_complex_imp<0>(mpfr_get_prec(val.data()))
+       : detail::mpc_complex_imp<0>(this->preserve_source_precision() ? mpfr_get_prec(val.data()) : multiprecision::detail::digits10_2_2(this->get_default_precision()))
    {
       mpc_set_fr(this->m_data, val.data(), GMP_RNDN);
    }
@@ -707,7 +707,8 @@ struct mpc_complex_backend<0> : public detail::mpc_complex_imp<0>
    template <unsigned D>
    mpc_complex_backend& operator=(const mpfr_float_backend<D>& val)
    {
-      mpc_set_prec(this->m_data, mpfr_get_prec(val.data()));
+      if(this->preserve_source_precision())
+         mpc_set_prec(this->m_data, mpfr_get_prec(val.data()));
       mpc_set_fr(this->m_data, val.data(), GMP_RNDN);
       return *this;
    }
@@ -1160,10 +1161,13 @@ inline void assign_components(mpc_complex_backend<D1>& result, const mpfr_float_
    // This is called from class number's constructors, so if we have variable
    // precision, then copy the precision of the source variables.
    //
-   if (!D1)
+   BOOST_IF_CONSTEXPR(!D1)
    {
-      unsigned long prec = (std::max)(mpfr_get_prec(a.data()), mpfr_get_prec(b.data()));
+      if ((result.thread_default_variable_precision_options() & variable_precision_options::precision_group) == variable_precision_options::preserve_source_precision)
-      mpc_set_prec(result.data(), prec);
+      {
+         unsigned long prec = (std::max)(mpfr_get_prec(a.data()), mpfr_get_prec(b.data()));
+         mpc_set_prec(result.data(), prec);
+      }
    }
    using default_ops::eval_fpclassify;
    if (eval_fpclassify(a) == (int)FP_NAN)

include/boost/multiprecision/mpfi.hpp

@@ -15,6 +15,7 @@
 #include <boost/math/special_functions/fpclassify.hpp>
 #include <boost/multiprecision/detail/big_lanczos.hpp>
 #include <boost/multiprecision/detail/digits.hpp>
+#include <boost/multiprecision/detail/precision.hpp>
 #include <boost/multiprecision/detail/atomic.hpp>
 #include <boost/multiprecision/traits/max_digits10.hpp>
 #include <boost/multiprecision/mpfr.hpp>
@@ -93,6 +94,13 @@ struct mpfi_float_imp
       if (o.m_data[0].left._mpfr_d)
          mpfi_set(m_data, o.m_data);
    }
+   template <unsigned D, mpfr_allocation_type AllocationType>
+   mpfi_float_imp(const mpfr_float_imp<D, AllocationType>& o)
+   {
+      mpfi_init2(m_data, preserve_source_precision() ? mpfr_get_prec(o.data()) : boost::multiprecision::detail::digits10_2_2(get_default_precision()));
+      if (o.data()[0]._mpfr_d)
+         mpfi_set_fr(m_data, o.data());
+   }
    // rvalue copy
    mpfi_float_imp(mpfi_float_imp&& o) noexcept
    {
@@ -386,6 +394,10 @@ struct mpfi_float_backend : public detail::mpfi_float_imp<digits10>
    {
       mpfi_set(this->m_data, val.data());
    }
+   template <unsigned D, mpfr_allocation_type AllocationType>
+   mpfi_float_backend(const mpfr_float_backend<D, AllocationType>& val, typename std::enable_if<D <= digits10>::type* = 0)
+       : detail::mpfi_float_imp<digits10>(val) {}
+
    template <unsigned D>
    explicit mpfi_float_backend(const mpfi_float_backend<D>& val, typename std::enable_if<!(D <= digits10)>::type* = 0)
        : detail::mpfi_float_imp<digits10>()
@@ -463,6 +475,11 @@ struct mpfi_float_backend<0> : public detail::mpfi_float_imp<0>
       mpfi_set(this->m_data, val);
    }
    mpfi_float_backend(const mpfi_float_backend& o) : detail::mpfi_float_imp<0>(o) {}
+
+   template <unsigned D, mpfr_allocation_type AllocationType>
+   mpfi_float_backend(const mpfr_float_backend<D, AllocationType>& val)
+       : detail::mpfi_float_imp<0>(val) {}
+
    // rvalue copy
    mpfi_float_backend(mpfi_float_backend&& o) noexcept : detail::mpfi_float_imp<0>(static_cast<detail::mpfi_float_imp<0>&&>(o))
    {}
@@ -475,6 +492,7 @@ struct mpfi_float_backend<0> : public detail::mpfi_float_imp<0>
    mpfi_float_backend(const V& a, const V& b, unsigned digits10)
        : detail::mpfi_float_imp<0>(multiprecision::detail::digits10_2_2(digits10))
    {
+      boost::multiprecision::detail::scoped_target_precision<mpfi_float_backend<0> > opts;
       assign_components(*this, a, b);
    }
 
@@ -850,6 +868,19 @@ inline void eval_convert_to(long double* result, const mpfi_float_backend<digits
 template <unsigned D1, unsigned D2, mpfr_allocation_type AllocationType>
 inline void assign_components(mpfi_float_backend<D1>& result, const mpfr_float_backend<D2, AllocationType>& a, const mpfr_float_backend<D2, AllocationType>& b)
 {
+   //
+   // This is called from class number's constructors, so if we have variable
+   // precision, then copy the precision of the source variables.
+   //
+   BOOST_IF_CONSTEXPR(!D1)
+   {
+      if ((result.thread_default_variable_precision_options() & variable_precision_options::precision_group) == variable_precision_options::preserve_source_precision)
+      {
+         unsigned long prec = (std::max)(mpfr_get_prec(a.data()), mpfr_get_prec(b.data()));
+         mpfi_set_prec(result.data(), prec);
+      }
+   }
+
    using default_ops::eval_fpclassify;
    if (eval_fpclassify(a) == (int)FP_NAN)
    {

include/boost/multiprecision/number.hpp

@@ -409,6 +409,23 @@ class number
    typename std::enable_if<std::is_convertible<V, self_type>::value, number<Backend, ExpressionTemplates>&>::type
       BOOST_MP_CXX14_CONSTEXPR operator+=(const V& v)
    {
+      detail::scoped_default_precision<number<Backend, ExpressionTemplates> > precision_guard(*this, v);
+      //
+      // If the current precision of *this differs from that of value v, then we
+      // create a temporary (which will have the correct precision thanks to precision_guard)
+      // and then move the result into *this.  In C++17 we add a leading "if constexpr"
+      // which causes this code to be eliminated in the common case that this type is
+      // not actually variable precision.  Pre C++17 this code should still be mostly
+      // optimised away, but we can't prevent instantiation of the dead code leading
+      // to longer build and possibly link times.
+      //
+      BOOST_MP_CONSTEXPR_IF_VARIABLE_PRECISION(number)
+         if (precision_guard.precision() != boost::multiprecision::detail::current_precision_of(*this))
+         {
+            number t(*this + v);
+            return *this = std::move(t);
+         }
+
       using default_ops::eval_add;
       eval_add(m_backend, canonical_value(v));
       return *this;
@@ -457,6 +474,23 @@ class number
    BOOST_MP_CXX14_CONSTEXPR typename std::enable_if<std::is_convertible<V, self_type>::value, number<Backend, ExpressionTemplates>&>::type
    operator-=(const V& v)
    {
+      detail::scoped_default_precision<number<Backend, ExpressionTemplates> > precision_guard(*this, v);
+      //
+      // If the current precision of *this differs from that of value v, then we
+      // create a temporary (which will have the correct precision thanks to precision_guard)
+      // and then move the result into *this.  In C++17 we add a leading "if constexpr"
+      // which causes this code to be eliminated in the common case that this type is
+      // not actually variable precision.  Pre C++17 this code should still be mostly
+      // optimised away, but we can't prevent instantiation of the dead code leading
+      // to longer build and possibly link times.
+      //
+      BOOST_MP_CONSTEXPR_IF_VARIABLE_PRECISION(number)
+         if (precision_guard.precision() != boost::multiprecision::detail::current_precision_of(*this))
+         {
+            number t(*this - v);
+            return *this = std::move(t);
+         }
+
       using default_ops::eval_subtract;
       eval_subtract(m_backend, canonical_value(v));
       return *this;
@@ -536,6 +570,23 @@ class number
    BOOST_MP_CXX14_CONSTEXPR typename std::enable_if<std::is_convertible<V, self_type>::value, number<Backend, ExpressionTemplates>&>::type
    operator*=(const V& v)
    {
+      detail::scoped_default_precision<number<Backend, ExpressionTemplates> > precision_guard(*this, v);
+      //
+      // If the current precision of *this differs from that of value v, then we
+      // create a temporary (which will have the correct precision thanks to precision_guard)
+      // and then move the result into *this.  In C++17 we add a leading "if constexpr"
+      // which causes this code to be eliminated in the common case that this type is
+      // not actually variable precision.  Pre C++17 this code should still be mostly
+      // optimised away, but we can't prevent instantiation of the dead code leading
+      // to longer build and possibly link times.
+      //
+      BOOST_MP_CONSTEXPR_IF_VARIABLE_PRECISION(number)
+         if (precision_guard.precision() != boost::multiprecision::detail::current_precision_of(*this))
+         {
+            number t(*this + v);
+            return *this = std::move(t);
+         }
+
       using default_ops::eval_multiply;
       eval_multiply(m_backend, canonical_value(v));
       return *this;
@@ -689,6 +740,23 @@ class number
    BOOST_MP_FORCEINLINE BOOST_MP_CXX14_CONSTEXPR typename std::enable_if<std::is_convertible<V, self_type>::value, number<Backend, ExpressionTemplates>&>::type
    operator/=(const V& v)
    {
+      detail::scoped_default_precision<number<Backend, ExpressionTemplates> > precision_guard(*this, v);
+      //
+      // If the current precision of *this differs from that of value v, then we
+      // create a temporary (which will have the correct precision thanks to precision_guard)
+      // and then move the result into *this.  In C++17 we add a leading "if constexpr"
+      // which causes this code to be eliminated in the common case that this type is
+      // not actually variable precision.  Pre C++17 this code should still be mostly
+      // optimised away, but we can't prevent instantiation of the dead code leading
+      // to longer build and possibly link times.
+      //
+      BOOST_MP_CONSTEXPR_IF_VARIABLE_PRECISION(number)
+         if (precision_guard.precision() != boost::multiprecision::detail::current_precision_of(*this))
+         {
+            number t(*this + v);
+            return *this = std::move(t);
+         }
+
       using default_ops::eval_divide;
       eval_divide(m_backend, canonical_value(v));
       return *this;

test/test_preserve_source_precision.cpp

@@ -101,6 +101,78 @@ void test()
    BOOST_CHECK_EQUAL(a.precision(), 100);
    a = new_value<T>();
    BOOST_CHECK_EQUAL(a.precision(), 35);
+
+   if constexpr (!std::is_same_v<T, typename T::value_type>)
+   {
+      //
+      // If we have a component type: ie we are an interval or a complex number, then
+      // operations involving the component type should match those of T:
+      //
+      using component_t = typename T::value_type;
+      component_t::thread_default_precision(100);
+      component_t::thread_default_variable_precision_options(boost::multiprecision::variable_precision_options::preserve_source_precision);
+
+      component_t cp1("0.1"), cp2("0.3"), cp3("0.11"), cp4("0.1231");
+
+      BOOST_CHECK_EQUAL(cp1.precision(), 100);
+      BOOST_CHECK_EQUAL(cp2.precision(), 100);
+
+      component_t::thread_default_precision(35);
+
+      T aa(cp1);
+      BOOST_CHECK_EQUAL(aa.precision(), 100);
+      T cc(cp1, cp2);
+      BOOST_CHECK_EQUAL(cc.precision(), 100);
+      T dd(cp1, cp2, 55);
+      BOOST_CHECK_EQUAL(dd.precision(), 55);
+      aa = new_value<T>();
+      BOOST_CHECK_EQUAL(aa.precision(), 35);
+      if constexpr (std::is_assignable_v<T, component_t>)
+      {
+         aa = cp1;
+         BOOST_CHECK_EQUAL(aa.precision(), 100);
+         aa = new_value<T>();
+         BOOST_CHECK_EQUAL(aa.precision(), 35);
+         aa = std::move(cp1);
+         BOOST_CHECK_EQUAL(aa.precision(), 100);
+         aa = new_value<T>();
+         BOOST_CHECK_EQUAL(aa.precision(), 35);
+      }
+      T bb(std::move(cp2));
+      BOOST_CHECK_EQUAL(bb.precision(), 100);
+      bb = new_value<T>();
+      BOOST_CHECK_EQUAL(bb.precision(), 35);
+
+      if constexpr (boost::multiprecision::is_compatible_arithmetic_type<component_t, T>::value)
+      {
+         aa = bb + cp3;
+         BOOST_CHECK_EQUAL(aa.precision(), 100);
+         aa = new_value<T>();
+         BOOST_CHECK_EQUAL(aa.precision(), 35);
+         aa = cp3 * bb;
+         BOOST_CHECK_EQUAL(aa.precision(), 100);
+         aa = new_value<T>();
+         BOOST_CHECK_EQUAL(aa.precision(), 35);
+         aa += cp3;
+         BOOST_CHECK_EQUAL(aa.precision(), 100);
+         aa = new_value<T>();
+         aa -= cp3;
+         BOOST_CHECK_EQUAL(aa.precision(), 100);
+         aa = new_value<T>();
+         BOOST_CHECK_EQUAL(aa.precision(), 35);
+         aa *= cp4;
+         BOOST_CHECK_EQUAL(aa.precision(), 100);
+         aa = new_value<T>();
+         aa /= cp4;
+         BOOST_CHECK_EQUAL(aa.precision(), 100);
+         aa = new_value<T>();
+         BOOST_CHECK_EQUAL(aa.precision(), 35);
+         aa -= bb * cp3;
+         BOOST_CHECK_EQUAL(aa.precision(), 100);
+         aa = new_value<T>();
+         BOOST_CHECK_EQUAL(aa.precision(), 35);
+      }
+   }
 }
 
 int main()

test/test_preserve_target_precision.cpp

@@ -77,6 +77,52 @@ void test()
    BOOST_CHECK_EQUAL(a.precision(), 35);
    a -= b * hp3;
    BOOST_CHECK_EQUAL(a.precision(), 35);
+
+   if constexpr (!std::is_same_v<T, typename T::value_type>)
+   {
+      //
+      // If we have a component type: ie we are an interval or a complex number, then
+      // operations involving the component type should match those of T:
+      //
+      using component_t = typename T::value_type;
+      component_t::thread_default_precision(100);
+      component_t::thread_default_variable_precision_options(boost::multiprecision::variable_precision_options::preserve_source_precision);
+
+      component_t cp1("0.1"), cp2("0.3"), cp3("0.11"), cp4("0.1231");
+
+      BOOST_CHECK_EQUAL(cp1.precision(), 100);
+      BOOST_CHECK_EQUAL(cp2.precision(), 100);
+
+      T::thread_default_precision(35);
+
+      T aa(cp1);
+      BOOST_CHECK_EQUAL(aa.precision(), 35);
+      T cc(cp1, cp2);
+      BOOST_CHECK_EQUAL(cc.precision(), 35);
+      T dd(cp1, cp2, 20);
+      BOOST_CHECK_EQUAL(dd.precision(), 20);
+      aa = cp1;
+      BOOST_CHECK_EQUAL(aa.precision(), 35);
+      aa = std::move(cp1);
+      BOOST_CHECK_EQUAL(aa.precision(), 35);
+      T bb(std::move(cp2));
+      BOOST_CHECK_EQUAL(bb.precision(), 35);
+
+      aa = bb + cp3;
+      BOOST_CHECK_EQUAL(aa.precision(), 35);
+      aa = cp3 * bb;
+      BOOST_CHECK_EQUAL(aa.precision(), 35);
+      aa += cp3;
+      BOOST_CHECK_EQUAL(aa.precision(), 35);
+      aa -= cp3;
+      BOOST_CHECK_EQUAL(aa.precision(), 35);
+      aa *= cp4;
+      BOOST_CHECK_EQUAL(aa.precision(), 35);
+      aa /= cp4;
+      BOOST_CHECK_EQUAL(aa.precision(), 35);
+      aa -= bb * cp3;
+      BOOST_CHECK_EQUAL(aa.precision(), 35);
+   }
 }
 
 int main()