Merge pull request #400 from ckormanyos/from_chars

Fixes #398 via impl and test from_chars()
ckormanyos · Jan 22, 2024 · 296f2c0 · 296f2c0
2 parents df1fa53 + 7183be8
commit 296f2c0
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Showing 4 changed files with 281 additions and 32 deletions.
diff --git a/README.md b/README.md
@@ -868,7 +868,14 @@ in the wide-integer project.
   - All wide-integer-types are move constructable.
   - All wide-integer types having the same widths and having the same limb-type (but possibly different sign) are move-assignable and `std::move()`-capable.
 
-### Importing and exporting bits
+### Importing and exporting characters and bits
+
+For sufficiently modern standards-conforming compilers,
+namespace-specific functions `to_chars()` and `from_chars()`
+are available. These each have the _usual_ `<charconv>`-like
+behavior and can also be used in `constexpr`-context.
+For motivational words on these, see also
+[issue 398](https://github.com/ckormanyos/wide-integer/issues/398).
 
 Support for importing and exporting bits is granted by the subroutines
 `import_bits()` and `export_bits()`. Their interfaces, input/output forms

diff --git a/math/wide_integer/uintwide_t.h b/math/wide_integer/uintwide_t.h
@@ -1,5 +1,5 @@
 ///////////////////////////////////////////////////////////////////
-//  Copyright Christopher Kormanyos 1999 - 2023.                 //
+//  Copyright Christopher Kormanyos 1999 - 2024.                 //
 //  Distributed under the Boost Software License,                //
 //  Version 1.0. (See accompanying file LICENSE_1_0.txt          //
 //  or copy at http://www.boost.org/LICENSE_1_0.txt)             //
@@ -1617,10 +1617,21 @@
            typename LimbType,
            typename AllocatorType,
            const bool IsSigned>
+  WIDE_INTEGER_CONSTEXPR
   auto to_chars(char* first,
                 char* last,
                 const uintwide_t<Width2, LimbType, AllocatorType, IsSigned>& x,
                 int base = static_cast<int>(INT8_C(10))) -> std::to_chars_result;
+
+  template<const size_t Width2,
+           typename LimbType,
+           typename AllocatorType,
+           const bool IsSigned>
+  WIDE_INTEGER_CONSTEXPR
+  auto from_chars(const char* first,
+                  const char* last,
+                  uintwide_t<Width2, LimbType, AllocatorType, IsSigned>& x,
+                  int base = static_cast<int>(INT8_C(10))) -> std::from_chars_result;
   #endif
 
   #if !defined(WIDE_INTEGER_DISABLE_TO_STRING)
@@ -2454,7 +2465,7 @@
           typename representation_type::allocator_type()
         }
     {
-      if(!rd_string(str_input))
+      if(!rd_string(str_input, (std::numeric_limits<unsigned_fast_type>::max)(), 0))
       {
         static_cast<void>(operator=((std::numeric_limits<uintwide_t>::max)()));
       }
@@ -3549,6 +3560,26 @@
   #endif
     friend auto ::test_uintwide_t_edge::test_various_isolated_edge_cases() -> bool;
 
+    template<const size_t OtherWidth2,
+             typename OtherLimbType,
+             typename OtherAllocatorType,
+             const bool OtherIsSignedLeft,
+             const bool OtherIsSignedRight>
+    friend WIDE_INTEGER_CONSTEXPR auto divmod(const uintwide_t<OtherWidth2, OtherLimbType, OtherAllocatorType, OtherIsSignedLeft >& a, // NOLINT(readability-redundant-declaration)
+                                              const uintwide_t<OtherWidth2, OtherLimbType, OtherAllocatorType, OtherIsSignedRight>& b,
+                                              std::enable_if_t<((!OtherIsSignedLeft) && (!OtherIsSignedRight)), int>* p_nullparam) -> std::pair<uintwide_t<OtherWidth2, OtherLimbType, OtherAllocatorType, OtherIsSignedLeft>, uintwide_t<OtherWidth2, OtherLimbType, OtherAllocatorType, OtherIsSignedRight>>;
+
+    #if (defined(__cpp_lib_to_chars) && (__cpp_lib_to_chars >= 201611L))
+    template<const size_t OtherWidth2,
+             typename OtherLimbType,
+             typename OtherAllocatorType,
+             const bool OtherIsSigned>
+    friend WIDE_INTEGER_CONSTEXPR auto from_chars(const char* first, // NOLINT(readability-redundant-declaration)
+                                                  const char* last,
+                                                  uintwide_t<OtherWidth2, OtherLimbType, OtherAllocatorType, OtherIsSigned>& x,
+                                                  int base) -> std::from_chars_result;
+    #endif
+
     template<const size_t OtherWidth2,
              typename OtherLimbType,
              typename OtherAllocatorType,
@@ -5331,13 +5362,15 @@
     }
 
     // Read string function.
-    WIDE_INTEGER_CONSTEXPR auto rd_string(const char* str_input) -> bool // NOLINT(readability-function-cognitive-complexity)
+    WIDE_INTEGER_CONSTEXPR auto rd_string(const char* str_input, const unsigned_fast_type count, const int base_hint) -> bool // NOLINT(readability-function-cognitive-complexity,bugprone-easily-swappable-parameters)
     {
       detail::fill_unsafe(values.begin(), values.end(), static_cast<limb_type>(UINT8_C(0)));
 
-      const auto str_length = detail::strlen_unsafe(str_input);
-
-      auto base = static_cast<std::uint_fast8_t>(UINT8_C(10));
+      const auto str_length =
+        static_cast<unsigned_fast_type>
+        (
+          (count == (std::numeric_limits<unsigned_fast_type>::max)()) ? detail::strlen_unsafe(str_input) : count
+        );
 
       auto pos = static_cast<unsigned_fast_type>(UINT8_C(0));
 
@@ -5359,33 +5392,41 @@
         ++pos;
       }
 
-      // Perform a dynamic detection of the base.
-      if(str_length > static_cast<unsigned_fast_type>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(0))))
+      // Set the base if the client has supplied a non-zero base-hint.
+      auto base = static_cast<std::uint_fast8_t>(base_hint);
+
+      if(base == static_cast<std::uint_fast8_t>(UINT8_C(0)))
       {
-        const auto might_be_oct_or_hex = ((str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(0)))] == '0') && (str_length > static_cast<unsigned_fast_type>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(0))))); // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
+        base = static_cast<std::uint_fast8_t>(UINT8_C(10));
 
-        if(might_be_oct_or_hex)
+        // Perform a dynamic detection of the base.
+        if(str_length > static_cast<unsigned_fast_type>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(0))))
         {
-          if((str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(1)))] >= '0') && (str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(1)))] <= '8')) // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
+          const auto might_be_oct_or_hex = ((str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(0)))] == '0') && (str_length > static_cast<unsigned_fast_type>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(0))))); // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
+
+          if(might_be_oct_or_hex)
           {
-            // The input format is octal.
-            base = static_cast<std::uint_fast8_t>(UINT8_C(8));
+            if((str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(1)))] >= '0') && (str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(1)))] <= '8')) // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
+            {
+              // The input format is octal.
+              base = static_cast<std::uint_fast8_t>(UINT8_C(8));
 
-            pos = static_cast<unsigned_fast_type>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(1)));
+              pos = static_cast<unsigned_fast_type>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(1)));
+            }
+            else if((str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(1)))] == 'x') || (str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(1)))] == 'X')) // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
+            {
+              // The input format is hexadecimal.
+              base = static_cast<std::uint_fast8_t>(UINT8_C(16));
+
+              pos = static_cast<unsigned_fast_type>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(2)));
+            }
           }
-          else if((str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(1)))] == 'x') || (str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(1)))] == 'X')) // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
+          else if((str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(0)))] >= '0') && (str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(0)))] <= '9')) // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
           {
-            // The input format is hexadecimal.
-            base = static_cast<std::uint_fast8_t>(UINT8_C(16));
-
-            pos = static_cast<unsigned_fast_type>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(2)));
+            // The input format is decimal.
+            ;
           }
         }
-        else if((str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(0)))] >= '0') && (str_input[static_cast<std::size_t>(static_cast<std::size_t>(pos) + static_cast<std::size_t>(UINT8_C(0)))] <= '9')) // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
-        {
-          // The input format is decimal.
-          ;
-        }
       }
 
       auto char_is_valid = true;
@@ -7283,6 +7324,7 @@
            typename LimbType,
            typename AllocatorType,
            const bool IsSigned>
+  WIDE_INTEGER_CONSTEXPR
   auto to_chars(char* first,
                 char* last,
                 const uintwide_t<Width2, LimbType, AllocatorType, IsSigned>& x,
@@ -7441,6 +7483,53 @@
 
     return result;
   }
+
+  template<const size_t Width2,
+           typename LimbType,
+           typename AllocatorType,
+           const bool IsSigned>
+  WIDE_INTEGER_CONSTEXPR
+  auto from_chars(const char* first,
+                  const char* last,
+                  uintwide_t<Width2, LimbType, AllocatorType, IsSigned>& x,
+                  int base) -> std::from_chars_result
+  {
+    using local_wide_integer_type = uintwide_t<Width2, LimbType, AllocatorType, IsSigned>;
+
+    using local_wide_integer_type = uintwide_t<Width2, LimbType, AllocatorType, IsSigned>;
+    using local_limb_type         = typename local_wide_integer_type::limb_type;
+
+    detail::fill_unsafe(x.values.begin(), x.values.end(), static_cast<local_limb_type>(UINT8_C(0)));
+
+    const auto str_len = static_cast<unsigned_fast_type>(detail::distance_unsafe(first, last));
+
+    const auto result_rd_string_is_ok = x.rd_string(first, str_len, base);
+
+    std::from_chars_result result { };
+
+    if(result_rd_string_is_ok)
+    {
+      result =
+        std::from_chars_result
+        {
+          last,
+          std::errc()
+        };
+    }
+    else
+    {
+      result =
+        std::from_chars_result
+        {
+          last,
+          std::errc::result_out_of_range
+        };
+
+      detail::fill_unsafe(x.values.begin(), x.values.end(), static_cast<local_limb_type>(UINT8_C(0)));
+    }
+
+    return result;
+  }
   #endif
 
   #if !defined(WIDE_INTEGER_DISABLE_TO_STRING)

diff --git a/test/test.cpp b/test/test.cpp
@@ -1,5 +1,5 @@
 ///////////////////////////////////////////////////////////////////
-//  Copyright Christopher Kormanyos 2018 - 2023.                 //
+//  Copyright Christopher Kormanyos 2018 - 2024.                 //
 //  Distributed under the Boost Software License,                //
 //  Version 1.0. (See accompanying file LICENSE_1_0.txt          //
 //  or copy at http://www.boost.org/LICENSE_1_0.txt)             //
@@ -11,8 +11,9 @@
 // When using local Boost-develop branch, use specific include paths.
 // -I/mnt/c/boost/modular_boost/boost/libs/config/include -I/mnt/c/boost/modular_boost/boost/libs/multiprecision/include
 
-// When using -std=c++14 and g++
+// When using -std=c++14/20 and g++
 // g++ -finline-functions -march=native -mtune=native -O3 -Wall -Wextra -Wpedantic -Wconversion -Wsign-conversion -std=c++14 -DWIDE_INTEGER_HAS_LIMB_TYPE_UINT64 -DWIDE_INTEGER_HAS_MUL_8_BY_8_UNROLL -I. -I/mnt/c/boost/boost_1_83_0 -pthread -lpthread test/test.cpp test/test_uintwide_t_boost_backend.cpp test/test_uintwide_t_edge_cases.cpp test/test_uintwide_t_examples.cpp test/test_uintwide_t_float_convert.cpp test/test_uintwide_t_int_convert.cpp test/test_uintwide_t_n_base.cpp test/test_uintwide_t_n_binary_ops_base.cpp examples/example000a_builtin_convert.cpp test/test_uintwide_t_spot_values.cpp examples/example000_numeric_limits.cpp examples/example001_mul_div.cpp examples/example001a_div_mod.cpp examples/example002_shl_shr.cpp examples/example003_sqrt.cpp examples/example003a_cbrt.cpp examples/example004_rootk_pow.cpp examples/example005_powm.cpp examples/example005a_pow_factors_of_p99.cpp examples/example006_gcd.cpp examples/example007_random_generator.cpp examples/example008_miller_rabin_prime.cpp examples/example008a_miller_rabin_prime.cpp examples/example009_timed_mul.cpp examples/example009a_timed_mul_4_by_4.cpp examples/example009b_timed_mul_8_by_8.cpp examples/example010_uint48_t.cpp examples/example011_uint24_t.cpp examples/example012_rsa_crypto.cpp examples/example013_ecdsa_sign_verify.cpp examples/example014_pi_spigot_wide.cpp -o wide_integer.exe
+// g++ -finline-functions -march=native -mtune=native -O3 -Wall -Wextra -Wpedantic -Wconversion -Wsign-conversion -std=c++20 -DWIDE_INTEGER_HAS_LIMB_TYPE_UINT64 -DWIDE_INTEGER_HAS_MUL_8_BY_8_UNROLL -I. -I/mnt/c/boost/boost_1_83_0 -pthread -lpthread test/test.cpp test/test_uintwide_t_boost_backend.cpp test/test_uintwide_t_edge_cases.cpp test/test_uintwide_t_examples.cpp test/test_uintwide_t_float_convert.cpp test/test_uintwide_t_int_convert.cpp test/test_uintwide_t_n_base.cpp test/test_uintwide_t_n_binary_ops_base.cpp examples/example000a_builtin_convert.cpp test/test_uintwide_t_spot_values.cpp examples/example000_numeric_limits.cpp examples/example001_mul_div.cpp examples/example001a_div_mod.cpp examples/example002_shl_shr.cpp examples/example003_sqrt.cpp examples/example003a_cbrt.cpp examples/example004_rootk_pow.cpp examples/example005_powm.cpp examples/example005a_pow_factors_of_p99.cpp examples/example006_gcd.cpp examples/example007_random_generator.cpp examples/example008_miller_rabin_prime.cpp examples/example008a_miller_rabin_prime.cpp examples/example009_timed_mul.cpp examples/example009a_timed_mul_4_by_4.cpp examples/example009b_timed_mul_8_by_8.cpp examples/example010_uint48_t.cpp examples/example011_uint24_t.cpp examples/example012_rsa_crypto.cpp examples/example013_ecdsa_sign_verify.cpp examples/example014_pi_spigot_wide.cpp -o wide_integer.exe
 
 // cd .tidy/make
 // make prepare -f make_tidy_01_generic.gmk MY_BOOST_ROOT=/mnt/c/boost/boost_1_83_0