From 66df6d63d158e65211cdcef866e2afa8fd4f4cfa Mon Sep 17 00:00:00 2001
From: ckormanyos <ckormanyos@yahoo.com>
Date: Tue, 7 Apr 2026 22:05:19 +0200
Subject: [PATCH 1/3] Attempt constepr-ification of hash functions

---
 include/boost/multiprecision/complex_adaptor.hpp     |  2 +-
 .../multiprecision/concepts/mp_number_archetypes.hpp |  2 +-
 include/boost/multiprecision/cpp_bin_float.hpp       |  2 +-
 include/boost/multiprecision/cpp_dec_float.hpp       |  2 +-
 .../cpp_df_qf/cpp_df_qf_detail_ccmath_limits.hpp     |  4 +++-
 include/boost/multiprecision/cpp_int/misc.hpp        |  2 +-
 include/boost/multiprecision/debug_adaptor.hpp       |  2 +-
 include/boost/multiprecision/detail/hash.hpp         | 12 ++++++------
 include/boost/multiprecision/float128.hpp            |  2 +-
 include/boost/multiprecision/gmp.hpp                 |  6 +++---
 include/boost/multiprecision/logged_adaptor.hpp      |  2 +-
 include/boost/multiprecision/mpc.hpp                 |  2 +-
 include/boost/multiprecision/mpfi.hpp                |  2 +-
 include/boost/multiprecision/mpfr.hpp                |  2 +-
 include/boost/multiprecision/number.hpp              |  8 ++++----
 include/boost/multiprecision/rational_adaptor.hpp    |  2 +-
 include/boost/multiprecision/tommath.hpp             |  2 +-
 17 files changed, 29 insertions(+), 27 deletions(-)

diff --git a/include/boost/multiprecision/complex_adaptor.hpp b/include/boost/multiprecision/complex_adaptor.hpp
index 40ec4d74d..4f08ed0b7 100644
--- a/include/boost/multiprecision/complex_adaptor.hpp
+++ b/include/boost/multiprecision/complex_adaptor.hpp
@@ -983,7 +983,7 @@ inline void eval_set_real(complex_adaptor<Backend>& result, const T& arg)
 }
 
 template <class Backend>
-inline std::size_t hash_value(const complex_adaptor<Backend>& val)
+constexpr std::size_t hash_value(const complex_adaptor<Backend>& val)
 {
    std::size_t result  = hash_value(val.real_data());
    std::size_t result2 = hash_value(val.imag_data());
diff --git a/include/boost/multiprecision/concepts/mp_number_archetypes.hpp b/include/boost/multiprecision/concepts/mp_number_archetypes.hpp
index 6c025ee44..71ced92e4 100644
--- a/include/boost/multiprecision/concepts/mp_number_archetypes.hpp
+++ b/include/boost/multiprecision/concepts/mp_number_archetypes.hpp
@@ -212,7 +212,7 @@ inline int eval_fpclassify(const number_backend_float_architype& arg)
    return BOOST_MP_FPCLASSIFY(arg.m_value);
 }
 
-inline std::size_t hash_value(const number_backend_float_architype& v)
+constexpr std::size_t hash_value(const number_backend_float_architype& v)
 {
    std::hash<long double> hasher;
    return hasher(v.m_value);
diff --git a/include/boost/multiprecision/cpp_bin_float.hpp b/include/boost/multiprecision/cpp_bin_float.hpp
index 487eb5270..9e6245d69 100644
--- a/include/boost/multiprecision/cpp_bin_float.hpp
+++ b/include/boost/multiprecision/cpp_bin_float.hpp
@@ -2075,7 +2075,7 @@ int eval_signbit(const cpp_bin_float<D1, B1, A1, E1, M1, M2>& val)
 }
 
 template <unsigned D1, backends::digit_base_type B1, class A1, class E1, E1 M1, E1 M2>
-inline std::size_t hash_value(const cpp_bin_float<D1, B1, A1, E1, M1, M2>& val)
+constexpr std::size_t hash_value(const cpp_bin_float<D1, B1, A1, E1, M1, M2>& val)
 {
    std::size_t result = hash_value(val.bits());
    boost::multiprecision::detail::hash_combine(result, val.exponent(), val.sign());
diff --git a/include/boost/multiprecision/cpp_dec_float.hpp b/include/boost/multiprecision/cpp_dec_float.hpp
index 27cf3d6b3..a264a30c3 100644
--- a/include/boost/multiprecision/cpp_dec_float.hpp
+++ b/include/boost/multiprecision/cpp_dec_float.hpp
@@ -3632,7 +3632,7 @@ inline int eval_signbit(const cpp_dec_float<Digits10, ExponentType, Allocator>&
 }
 
 template <unsigned Digits10, class ExponentType, class Allocator>
-inline std::size_t hash_value(const cpp_dec_float<Digits10, ExponentType, Allocator>& val)
+constexpr std::size_t hash_value(const cpp_dec_float<Digits10, ExponentType, Allocator>& val)
 {
    return val.hash();
 }
diff --git a/include/boost/multiprecision/cpp_df_qf/cpp_df_qf_detail_ccmath_limits.hpp b/include/boost/multiprecision/cpp_df_qf/cpp_df_qf_detail_ccmath_limits.hpp
index 7f364b844..6c09a16d2 100644
--- a/include/boost/multiprecision/cpp_df_qf/cpp_df_qf_detail_ccmath_limits.hpp
+++ b/include/boost/multiprecision/cpp_df_qf/cpp_df_qf_detail_ccmath_limits.hpp
@@ -180,7 +180,9 @@ struct numeric_limits<FloatingPointType,
    static constexpr auto epsilon() -> self_type
    {
      // This double value has only one bit set and so is exact.
-     return 1.92592994438723585305597794258492732e-34;
+     // N[2^-112, 84]
+
+     return 1.92592994438723585305597794258492731853810164821538819523993879556655883789062500000e-34;
    }
 
    static constexpr auto round_error() noexcept -> self_type { return static_cast<self_type>(0.5F); }
diff --git a/include/boost/multiprecision/cpp_int/misc.hpp b/include/boost/multiprecision/cpp_int/misc.hpp
index c464cfae1..d2504db7b 100644
--- a/include/boost/multiprecision/cpp_int/misc.hpp
+++ b/include/boost/multiprecision/cpp_int/misc.hpp
@@ -1406,7 +1406,7 @@ eval_msb(const cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocato
 }
 
 template <std::size_t MinBits1, std::size_t MaxBits1, cpp_integer_type SignType1, cpp_int_check_type Checked1, class Allocator1>
-inline BOOST_MP_CXX14_CONSTEXPR std::size_t hash_value(const cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>& val) noexcept
+constexpr std::size_t hash_value(const cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>& val) noexcept
 {
    std::size_t result = 0;
    for (std::size_t i = 0; i < val.size(); ++i)
diff --git a/include/boost/multiprecision/debug_adaptor.hpp b/include/boost/multiprecision/debug_adaptor.hpp
index 08b11386a..1879e5c4b 100644
--- a/include/boost/multiprecision/debug_adaptor.hpp
+++ b/include/boost/multiprecision/debug_adaptor.hpp
@@ -562,7 +562,7 @@ int eval_signbit(const debug_adaptor<Backend>& val)
 }
 
 template <class Backend>
-std::size_t hash_value(const debug_adaptor<Backend>& val)
+constexpr std::size_t hash_value(const debug_adaptor<Backend>& val)
 {
    return hash_value(val.value());
 }
diff --git a/include/boost/multiprecision/detail/hash.hpp b/include/boost/multiprecision/detail/hash.hpp
index 664680f80..9b6bd3121 100644
--- a/include/boost/multiprecision/detail/hash.hpp
+++ b/include/boost/multiprecision/detail/hash.hpp
@@ -13,7 +13,7 @@
 namespace boost { namespace multiprecision { namespace detail {
 
 template <typename T>
-inline std::size_t hash_value(const T& v)
+BOOST_MP_CXX14_CONSTEXPR std::size_t hash_value(const T& v)
 {
     std::hash<T> hasher;
     return hasher(v);
@@ -21,19 +21,19 @@ inline std::size_t hash_value(const T& v)
 
 #if defined(BOOST_HAS_INT128)
 
-std::size_t hash_value(const uint128_type& val);
+constexpr std::size_t hash_value(const uint128_type& val);
 
-inline std::size_t hash_value(const int128_type& val)
+constexpr std::size_t hash_value(const int128_type& val)
 {
    return hash_value(static_cast<uint128_type>(val));
 }
 
 #endif
 
-inline void hash_combine(std::size_t&) {}
+constexpr void hash_combine(std::size_t&) {}
 
 template <typename T, typename... Args>
-inline void hash_combine(std::size_t& seed, const T& v, Args... args) 
+constexpr void hash_combine(std::size_t& seed, const T& v, Args... args) 
 {
     constexpr std::size_t adder = 0x9e3779b9;
     seed = seed ^ (hash_value(v) + adder + (seed<<6) + (seed>>2));
@@ -42,7 +42,7 @@ inline void hash_combine(std::size_t& seed, const T& v, Args... args)
 
 #if defined(BOOST_HAS_INT128)
 
-inline std::size_t hash_value(const uint128_type& val)
+constexpr std::size_t hash_value(const uint128_type& val)
 {
    std::size_t result = static_cast<std::size_t>(val);
    hash_combine(result, static_cast<std::size_t>(val >> 64));
diff --git a/include/boost/multiprecision/float128.hpp b/include/boost/multiprecision/float128.hpp
index 81d7be741..439135957 100644
--- a/include/boost/multiprecision/float128.hpp
+++ b/include/boost/multiprecision/float128.hpp
@@ -634,7 +634,7 @@ inline int eval_signbit BOOST_PREVENT_MACRO_SUBSTITUTION(const float128_backend&
 }
 #endif
 
-inline std::size_t hash_value(const float128_backend& val)
+constexpr std::size_t hash_value(const float128_backend& val)
 {
    return boost::multiprecision::detail::hash_value(static_cast<double>(val.value()));
 }
diff --git a/include/boost/multiprecision/gmp.hpp b/include/boost/multiprecision/gmp.hpp
index e15e2604a..1cc673f4f 100644
--- a/include/boost/multiprecision/gmp.hpp
+++ b/include/boost/multiprecision/gmp.hpp
@@ -1384,7 +1384,7 @@ inline void eval_frexp(gmp_float<Digits10>& result, const gmp_float<Digits10>& v
 }
 
 template <unsigned Digits10>
-inline std::size_t hash_value(const gmp_float<Digits10>& val)
+constexpr std::size_t hash_value(const gmp_float<Digits10>& val)
 {
    std::size_t result = 0;
    for (int i = 0; i < std::abs(val.data()[0]._mp_size); ++i)
@@ -2353,7 +2353,7 @@ eval_powm(gmp_int& result, const gmp_int& base, Integer p, const gmp_int& m)
    mpz_powm_ui(result.data(), base.data(), p, m.data());
 }
 
-inline std::size_t hash_value(const gmp_int& val)
+constexpr std::size_t hash_value(const gmp_int& val)
 {
    // We should really use mpz_limbs_read here, but that's unsupported on older versions:
    std::size_t result = 0;
@@ -3131,7 +3131,7 @@ void assign_components(gmp_rational& result, const T& a, const gmp_int& b)
 }
 
 
-inline std::size_t hash_value(const gmp_rational& val)
+constexpr std::size_t hash_value(const gmp_rational& val)
 {
    std::size_t result = 0;
    for (int i = 0; i < std::abs(val.data()[0]._mp_num._mp_size); ++i)
diff --git a/include/boost/multiprecision/logged_adaptor.hpp b/include/boost/multiprecision/logged_adaptor.hpp
index acdfb53b1..19399e46f 100644
--- a/include/boost/multiprecision/logged_adaptor.hpp
+++ b/include/boost/multiprecision/logged_adaptor.hpp
@@ -645,7 +645,7 @@ int eval_signbit(const logged_adaptor<Backend>& val)
 }
 
 template <class Backend>
-std::size_t hash_value(const logged_adaptor<Backend>& val)
+constexpr std::size_t hash_value(const logged_adaptor<Backend>& val)
 {
    return hash_value(val.value());
 }
diff --git a/include/boost/multiprecision/mpc.hpp b/include/boost/multiprecision/mpc.hpp
index 48c622aed..3649ec2f6 100644
--- a/include/boost/multiprecision/mpc.hpp
+++ b/include/boost/multiprecision/mpc.hpp
@@ -1650,7 +1650,7 @@ inline void eval_set_imag(mpc_complex_backend<Digits10>& result, const long long
 #endif
 
 template <unsigned Digits10>
-inline std::size_t hash_value(const mpc_complex_backend<Digits10>& val)
+constexpr std::size_t hash_value(const mpc_complex_backend<Digits10>& val)
 {
    std::size_t result = 0;
    std::size_t len    = val.data()[0].re[0]._mpfr_prec / mp_bits_per_limb;
diff --git a/include/boost/multiprecision/mpfi.hpp b/include/boost/multiprecision/mpfi.hpp
index 828ee338e..e8055668c 100644
--- a/include/boost/multiprecision/mpfi.hpp
+++ b/include/boost/multiprecision/mpfi.hpp
@@ -1310,7 +1310,7 @@ inline void eval_log2(mpfi_float_backend<Digits10>& result, const mpfi_float_bac
 }
 
 template <unsigned Digits10>
-inline std::size_t hash_value(const mpfi_float_backend<Digits10>& val)
+constexpr std::size_t hash_value(const mpfi_float_backend<Digits10>& val)
 {
    std::size_t result = 0;
    std::size_t len    = val.left_data()[0]._mpfr_prec / mp_bits_per_limb;
diff --git a/include/boost/multiprecision/mpfr.hpp b/include/boost/multiprecision/mpfr.hpp
index c426da53c..903ff0eb5 100644
--- a/include/boost/multiprecision/mpfr.hpp
+++ b/include/boost/multiprecision/mpfr.hpp
@@ -1979,7 +1979,7 @@ inline int eval_signbit BOOST_PREVENT_MACRO_SUBSTITUTION(const mpfr_float_backen
 }
 
 template <unsigned Digits10, mpfr_allocation_type AllocateType>
-inline std::size_t hash_value(const mpfr_float_backend<Digits10, AllocateType>& val)
+constexpr std::size_t hash_value(const mpfr_float_backend<Digits10, AllocateType>& val)
 {
    std::size_t result = 0;
    std::size_t len    = val.data()[0]._mpfr_prec / mp_bits_per_limb;
diff --git a/include/boost/multiprecision/number.hpp b/include/boost/multiprecision/number.hpp
index aac21d3cc..35d4b50ff 100644
--- a/include/boost/multiprecision/number.hpp
+++ b/include/boost/multiprecision/number.hpp
@@ -2364,7 +2364,7 @@ BOOST_MP_FORCEINLINE BOOST_MP_CXX14_CONSTEXPR void swap(number<Backend, Expressi
 // Boost.Hash support, just call hash_value for the backend, which may or may not be supported:
 //
 template <class Backend, expression_template_option ExpressionTemplates>
-inline BOOST_MP_CXX14_CONSTEXPR std::size_t hash_value(const number<Backend, ExpressionTemplates>& val)
+constexpr std::size_t hash_value(const number<Backend, ExpressionTemplates>& val)
 {
    return hash_value(val.backend());
 }
@@ -2443,7 +2443,7 @@ inline BOOST_MP_CXX14_CONSTEXPR multiprecision::number<T, ExpressionTemplates> d
 }
 
 template <class T, multiprecision::expression_template_option ExpressionTemplates>
-inline BOOST_MP_CXX14_CONSTEXPR std::size_t hash_value(const rational<multiprecision::number<T, ExpressionTemplates> >& val)
+constexpr std::size_t hash_value(const rational<multiprecision::number<T, ExpressionTemplates> >& val)
 {
    std::size_t result = hash_value(val.numerator());
    boost::multiprecision::detail::hash_combine(result, hash_value(val.denominator()));
@@ -2471,12 +2471,12 @@ namespace std {
 template <class Backend, boost::multiprecision::expression_template_option ExpressionTemplates>
 struct hash<boost::multiprecision::number<Backend, ExpressionTemplates> >
 {
-   BOOST_MP_CXX14_CONSTEXPR std::size_t operator()(const boost::multiprecision::number<Backend, ExpressionTemplates>& val) const { return hash_value(val); }
+   constexpr std::size_t operator()(const boost::multiprecision::number<Backend, ExpressionTemplates>& val) const { return hash_value(val); }
 };
 template <class Backend, boost::multiprecision::expression_template_option ExpressionTemplates>
 struct hash<boost::rational<boost::multiprecision::number<Backend, ExpressionTemplates> > >
 {
-   BOOST_MP_CXX14_CONSTEXPR std::size_t operator()(const boost::rational<boost::multiprecision::number<Backend, ExpressionTemplates> >& val) const
+   constexpr std::size_t operator()(const boost::rational<boost::multiprecision::number<Backend, ExpressionTemplates> >& val) const
    {
       std::size_t result = hash_value(val.numerator());
       boost::multiprecision::detail::hash_combine(result, hash_value(val.denominator()));
diff --git a/include/boost/multiprecision/rational_adaptor.hpp b/include/boost/multiprecision/rational_adaptor.hpp
index 8a024719d..7694bbf28 100644
--- a/include/boost/multiprecision/rational_adaptor.hpp
+++ b/include/boost/multiprecision/rational_adaptor.hpp
@@ -417,7 +417,7 @@ inline typename std::enable_if<number_category<R>::value == number_kind_integer>
 // Hashing support, not strictly required, but it is used in our tests:
 //
 template <class Backend>
-inline std::size_t hash_value(const rational_adaptor<Backend>& arg)
+constexpr std::size_t hash_value(const rational_adaptor<Backend>& arg)
 {
    std::size_t result = hash_value(arg.num());
    std::size_t result2 = hash_value(arg.denom());
diff --git a/include/boost/multiprecision/tommath.hpp b/include/boost/multiprecision/tommath.hpp
index 52db1b76f..5ed035d40 100644
--- a/include/boost/multiprecision/tommath.hpp
+++ b/include/boost/multiprecision/tommath.hpp
@@ -899,7 +899,7 @@ inline typename std::enable_if<boost::multiprecision::detail::is_signed<Integer>
    return eval_integer_modulus(x, boost::multiprecision::detail::unsigned_abs(val));
 }
 
-inline std::size_t hash_value(const tommath_int& val)
+constexpr std::size_t hash_value(const tommath_int& val)
 {
    std::size_t result = 0;
    std::size_t len    = val.data().used;

From 40cf9e50603a27b073a3349bdefa7b838f550405 Mon Sep 17 00:00:00 2001
From: ckormanyos <ckormanyos@yahoo.com>
Date: Tue, 7 Apr 2026 23:01:55 +0200
Subject: [PATCH 2/3] Relax constexpr-ness of a std-function

---
 include/boost/multiprecision/concepts/mp_number_archetypes.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/boost/multiprecision/concepts/mp_number_archetypes.hpp b/include/boost/multiprecision/concepts/mp_number_archetypes.hpp
index 71ced92e4..69c5b9dd2 100644
--- a/include/boost/multiprecision/concepts/mp_number_archetypes.hpp
+++ b/include/boost/multiprecision/concepts/mp_number_archetypes.hpp
@@ -212,7 +212,7 @@ inline int eval_fpclassify(const number_backend_float_architype& arg)
    return BOOST_MP_FPCLASSIFY(arg.m_value);
 }
 
-constexpr std::size_t hash_value(const number_backend_float_architype& v)
+inline BOOST_MP_CXX14_CONSTEXPR std::size_t hash_value(const number_backend_float_architype& v)
 {
    std::hash<long double> hasher;
    return hasher(v.m_value);

From b0fe49f4f7d8e6734624d1996daba11f448cb46a Mon Sep 17 00:00:00 2001
From: ckormanyos <ckormanyos@yahoo.com>
Date: Tue, 7 Apr 2026 23:03:36 +0200
Subject: [PATCH 3/3] Correct old-style constexpr-ness

---
 include/boost/multiprecision/concepts/mp_number_archetypes.hpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/boost/multiprecision/concepts/mp_number_archetypes.hpp b/include/boost/multiprecision/concepts/mp_number_archetypes.hpp
index 69c5b9dd2..4139b89cf 100644
--- a/include/boost/multiprecision/concepts/mp_number_archetypes.hpp
+++ b/include/boost/multiprecision/concepts/mp_number_archetypes.hpp
@@ -214,7 +214,8 @@ inline int eval_fpclassify(const number_backend_float_architype& arg)
 
 inline BOOST_MP_CXX14_CONSTEXPR std::size_t hash_value(const number_backend_float_architype& v)
 {
-   std::hash<long double> hasher;
+   std::hash<long double> hasher { };
+
    return hasher(v.m_value);
 }