change dragon4 implementation

Author: jaja360

.gitignore

@@ -1,4 +1,5 @@
 build
 build_debug
 build_script
+compile_commands.json
 .cache

README.md

@@ -6,7 +6,7 @@ numbers, i.e., converting them from an IEEE 754 binary representation to a
 string decimal representation.
 
 Currently, the following approaches are compared:
-  - [dragon4](https://github.com/abolz/Drachennest/blob/master/src/dragon4.cc)
+  - [dragon4](https://github.com/ahaldane/Dragon4)
   - [std::to_string](https://en.cppreference.com/w/cpp/string/basic_string/to_string)
   - [fmt::format](https://github.com/fmtlib/fmt)
   - [netlib](https://github.com/jwiegley/gdtoa)

benchmarks/CMakeLists.txt

@@ -76,4 +76,5 @@ if(teju_has_float128)
 endif()
 target_link_libraries(benchmark PUBLIC dragonbox::dragonbox_to_chars)
 target_link_libraries(benchmark PUBLIC dragon_schubfach_lib)
+target_link_libraries(benchmark PUBLIC dragon4_lib)
 target_include_directories(benchmark PUBLIC ${grisu-exact_SOURCE_DIR})

benchmarks/algorithms.h

@@ -22,8 +22,8 @@
 #include <span>
 
 #include "cpp/common/traits.hpp"  // Teju Jagua
+#include "PrintFloat.h"  // Dragon4
 #include "double-conversion/double-conversion.h"
-#include "dragon4.h"
 #include "dragonbox/dragonbox_to_chars.h"
 #include "grisu2.h"
 #include "grisu3.h"
@@ -73,17 +73,14 @@ struct BenchArgs {
   unsigned char testRepeat{100};
 };
 
-// No dragon4 implementation optimized for float instead of double ?
 template<arithmetic_float T>
 int dragon4(T d, std::span<char>& buffer) {
-  using IEEE754Type
-      = std::conditional_t<std::is_same_v<T, float>, IEEE754f, IEEE754d>;
-  const IEEE754Type fields = decode_ieee754(d);
-
-  uint64_t dm;
-  int dexp;
-  dragon4::Dragon4(dm, dexp, fields.mantissa, fields.exponent, true, true);
-  return to_chars(dm, dexp, fields.sign, buffer.data());
+  if constexpr (std::is_same_v<T, float>)
+    return PrintFloat32(buffer.data(), buffer.size(), d,
+                        PrintFloatFormat_Positional, -1);
+  else
+    return PrintFloat64(buffer.data(), buffer.size(), d,
+                        PrintFloatFormat_Positional, -1);
 }
 
 // No errol3 implementation optimized for float instead of double ?

benchmarks/benchmark.cpp

@@ -145,13 +145,6 @@ int main(int argc, char **argv) {
         cxxopts::value<bool>()->default_value("false"))
         ("t,test", "Test the algorithms and find their properties.",
         cxxopts::value<bool>()->default_value("false"))
-        ("d,dragon", "Enable dragon4 (current impl. triggers some asserts).",
-#ifdef NDEBUG
-        cxxopts::value<bool>()->default_value("true"))
-#else // NDEBUG
-        // dragon4 is not safe in debug mode: some asserts fire.
-        cxxopts::value<bool>()->default_value("false"))
-#endif
         ("e,errol", "Enable errol3 (current impl. returns invalid values, e.g., for 0).",
         cxxopts::value<bool>()->default_value("false"))
         ("h,help", "Print usage.");
@@ -189,7 +182,7 @@ int main(int argc, char **argv) {
     auto initArgs = [&](auto type) {
       using T = decltype(type);
       std::array<BenchArgs<T>, Benchmarks::COUNT> args;
-      args[Benchmarks::DRAGON4]           = { "dragon4"           , Benchmarks::dragon4<T>           , result["dragon"].as<bool>()   , 10 };
+      args[Benchmarks::DRAGON4]           = { "dragon4"           , Benchmarks::dragon4<T>           , true                          , 10 };
       args[Benchmarks::ERROL3]            = { "errol3"            , Benchmarks::errol3<T>            , result["errol"].as<bool>() };
       args[Benchmarks::TO_STRING]         = { "std::to_string"    , Benchmarks::to_string<T>         , ERROL_SUPPORTED };
       args[Benchmarks::FMT_FORMAT]        = { "fmt::format"       , Benchmarks::fmt_format<T>        , true };

benchmarks/ieeeToString.cpp

@@ -1,13 +1,14 @@
 #include "ieeeToString.h"
 
+#include <bit>
 #include <cassert>
 #include <cstring>
 
 #include "ryu/digit_table.h" // For DIGIT_TABLE
 #include "ryu/common.h" // For decimalLength9
 
 IEEE754f decode_ieee754(float f) {
-  const uint32_t& bits = reinterpret_cast<const uint32_t&>(f);
+  const uint32_t bits = std::bit_cast<uint32_t>(f);
 
   IEEE754f decomposed;
   decomposed.exponent = (bits >> FloatMantissaBits) & ((1 << FloatExponentBits) - 1);
@@ -17,7 +18,7 @@ IEEE754f decode_ieee754(float f) {
 }
 
 IEEE754d decode_ieee754(double f) {
-  const uint64_t& bits = reinterpret_cast<const uint64_t&>(f);
+  const uint64_t bits = std::bit_cast<uint64_t>(f);
 
   IEEE754d decomposed;
   decomposed.exponent = (bits >> DoubleMantissaBits) & ((1ull << DoubleExponentBits) - 1);

dependencies/CMakeLists.txt

@@ -78,7 +78,27 @@ FetchContent_Declare(
 FetchContent_MakeAvailable(dragonbox)
 
 FetchContent_Declare(
-        drachennest # for schubfach and dragon4
+        dragon4
+        GIT_REPOSITORY https://github.com/ahaldane/Dragon4.git
+        GIT_TAG 670a3827651c68c9f329d394898b1204cb5ec46f
+        GIT_SHALLOW TRUE
+)
+FetchContent_GetProperties(dragon4)
+if(NOT dragon4)
+  FetchContent_Populate(dragon4)  # Downloads code to ${dragon4_SOURCE_DIR}
+endif()
+set(dragon4_SOURCE_DIR ${dragon4_SOURCE_DIR} PARENT_SCOPE)
+add_library(dragon4_lib STATIC
+    ${dragon4_SOURCE_DIR}/Dragon4.cpp
+    ${dragon4_SOURCE_DIR}/Math.cpp
+    ${dragon4_SOURCE_DIR}/PrintFloat.cpp
+)
+target_include_directories(dragon4_lib PUBLIC
+    ${dragon4_SOURCE_DIR}
+)
+
+FetchContent_Declare(
+        drachennest # for schubfach
         GIT_REPOSITORY https://github.com/abolz/Drachennest.git
         GIT_TAG e6714a39ad331b4489d0b6aaf3968635bff4eb5e
         GIT_SHALLOW TRUE
@@ -94,7 +114,6 @@ add_library(dragon_schubfach_lib STATIC
     ${drachennest_SOURCE_DIR}/src/schubfach_64.cc
     ${drachennest_SOURCE_DIR}/src/grisu3.cc
     ${drachennest_SOURCE_DIR}/src/grisu2.cc
-
 )
 target_include_directories(dragon_schubfach_lib PUBLIC
     ${drachennest_SOURCE_DIR}/src