Merge branch 'main' of github.com:fastfloat/fast_float

.github/workflows/ubuntu20-fastmath.yml

@@ -0,0 +1,18 @@
+name: Ubuntu 20.04 CI (GCC 9, fast-math)
+
+on: [push, pull_request]
+
+jobs:
+  ubuntu-build:
+    runs-on: ubuntu-20.04
+    strategy:
+      fail-fast: false
+    steps:
+      - uses: actions/checkout@v3
+      - name: Use cmake
+        run: |
+          mkdir build &&
+          cd build &&
+          cmake -DCMAKE_CXX_FLAGS="-ffast-math" -DFASTFLOAT_TEST=ON ..  &&
+          cmake --build .   &&
+          ctest --output-on-failure

include/fast_float/bigint.h

@@ -17,7 +17,7 @@ namespace fast_float {
 // we might have platforms where `CHAR_BIT` is not 8, so let's avoid
 // doing `8 * sizeof(limb)`.
 #if defined(FASTFLOAT_64BIT) && !defined(__sparc)
-#define FASTFLOAT_64BIT_LIMB
+#define FASTFLOAT_64BIT_LIMB 1
 typedef uint64_t limb;
 constexpr size_t limb_bits = 64;
 #else

include/fast_float/float_common.h

@@ -12,11 +12,11 @@
        || defined(__MINGW64__)                                          \
        || defined(__s390x__)                                            \
        || (defined(__ppc64__) || defined(__PPC64__) || defined(__ppc64le__) || defined(__PPC64LE__)) )
-#define FASTFLOAT_64BIT
+#define FASTFLOAT_64BIT 1
 #elif (defined(__i386) || defined(__i386__) || defined(_M_IX86)   \
      || defined(__arm__) || defined(_M_ARM)                   \
      || defined(__MINGW32__) || defined(__EMSCRIPTEN__))
-#define FASTFLOAT_32BIT
+#define FASTFLOAT_32BIT 1
 #else
   // Need to check incrementally, since SIZE_MAX is a size_t, avoid overflow.
   // We can never tell the register width, but the SIZE_MAX is a good approximation.
@@ -24,9 +24,9 @@
   #if SIZE_MAX == 0xffff
     #error Unknown platform (16-bit, unsupported)
   #elif SIZE_MAX == 0xffffffff
-    #define FASTFLOAT_32BIT
+    #define FASTFLOAT_32BIT 1
   #elif SIZE_MAX == 0xffffffffffffffff
-    #define FASTFLOAT_64BIT
+    #define FASTFLOAT_64BIT 1
   #else
     #error Unknown platform (not 32-bit, not 64-bit?)
   #endif
@@ -272,10 +272,12 @@ template <typename T> struct binary_format {
   static inline constexpr int minimum_exponent();
   static inline constexpr int infinite_power();
   static inline constexpr int sign_index();
+  static inline constexpr int min_exponent_fast_path(); // used when fegetround() == FE_TONEAREST
   static inline constexpr int max_exponent_fast_path();
   static inline constexpr int max_exponent_round_to_even();
   static inline constexpr int min_exponent_round_to_even();
   static inline constexpr uint64_t max_mantissa_fast_path(int64_t power);
+  static inline constexpr uint64_t max_mantissa_fast_path(); // used when fegetround() == FE_TONEAREST
   static inline constexpr int largest_power_of_ten();
   static inline constexpr int smallest_power_of_ten();
   static inline constexpr T exact_power_of_ten(int64_t power);
@@ -285,6 +287,22 @@ template <typename T> struct binary_format {
   static inline constexpr equiv_uint hidden_bit_mask();
 };
 
+template <> inline constexpr int binary_format<double>::min_exponent_fast_path() {
+#if (FLT_EVAL_METHOD != 1) && (FLT_EVAL_METHOD != 0)
+  return 0;
+#else
+  return -22;
+#endif
+}
+
+template <> inline constexpr int binary_format<float>::min_exponent_fast_path() {
+#if (FLT_EVAL_METHOD != 1) && (FLT_EVAL_METHOD != 0)
+  return 0;
+#else
+  return -10;
+#endif
+}
+
 template <> inline constexpr int binary_format<double>::mantissa_explicit_bits() {
   return 52;
 }
@@ -331,13 +349,18 @@ template <> inline constexpr int binary_format<double>::max_exponent_fast_path()
 template <> inline constexpr int binary_format<float>::max_exponent_fast_path() {
   return 10;
 }
-
+template <> inline constexpr uint64_t binary_format<double>::max_mantissa_fast_path() {
+  return uint64_t(2) << mantissa_explicit_bits();
+}
 template <> inline constexpr uint64_t binary_format<double>::max_mantissa_fast_path(int64_t power) {
   // caller is responsible to ensure that
   // power >= 0 && power <= 22
   //
   return max_mantissa_double[power];
 }
+template <> inline constexpr uint64_t binary_format<float>::max_mantissa_fast_path() {
+  return uint64_t(2) << mantissa_explicit_bits();
+}
 template <> inline constexpr uint64_t binary_format<float>::max_mantissa_fast_path(int64_t power) {
   // caller is responsible to ensure that
   // power >= 0 && power <= 10

include/fast_float/parse_number.h

@@ -60,6 +60,48 @@ from_chars_result parse_infnan(const char *first, const char *last, T &value)  n
   return answer;
 }
 
+/**
+ * Returns true if the floating-pointing rounding mode is to 'nearest'.
+ * It is the default on most system. This function is meant to be inexpensive.
+ * Credit : @mwalcott3
+ */
+fastfloat_really_inline bool rounds_to_nearest() noexcept {
+  // See
+  // A fast function to check your floating-point rounding mode
+  // https://lemire.me/blog/2022/11/16/a-fast-function-to-check-your-floating-point-rounding-mode/
+  //
+  // This function is meant to be equivalent to :
+  // prior: #include <cfenv>
+  //  return fegetround() == FE_TONEAREST;
+  // However, it is expected to be much faster than the fegetround()
+  // function call.
+  //
+  // The volatile keywoard prevents the compiler from computing the function
+  // at compile-time.
+  // There might be other ways to prevent compile-time optimizations (e.g., asm).
+  // The value does not need to be std::numeric_limits<float>::min(), any small
+  // value so that 1 + x should round to 1 would do (after accounting for excess
+  // precision, as in 387 instructions).
+  static volatile float fmin = std::numeric_limits<float>::min();
+  float fmini = fmin; // we copy it so that it gets loaded at most once.
+  //
+  // Explanation:
+  // Only when fegetround() == FE_TONEAREST do we have that
+  // fmin + 1.0f == 1.0f - fmin.
+  //
+  // FE_UPWARD:
+  //  fmin + 1.0f > 1
+  //  1.0f - fmin == 1
+  //
+  // FE_DOWNWARD or  FE_TOWARDZERO:
+  //  fmin + 1.0f == 1
+  //  1.0f - fmin < 1
+  //
+  // Note: This may fail to be accurate if fast-math has been
+  // enabled, as rounding conventions may not apply.
+  return (fmini + 1.0f == 1.0f - fmini);
+}
+
 } // namespace detail
 
 template<typename T>
@@ -87,12 +129,45 @@ from_chars_result from_chars_advanced(const char *first, const char *last,
   }
   answer.ec = std::errc(); // be optimistic
   answer.ptr = pns.lastmatch;
-  // Next is a modified Clinger's fast path, inspired by Jakub Jelínek's proposal
+  // The implementation of the Clinger's fast path is convoluted because
-  if (pns.exponent >= 0 && pns.exponent <= binary_format<T>::max_exponent_fast_path() && pns.mantissa <=binary_format<T>::max_mantissa_fast_path(pns.exponent) && !pns.too_many_digits) {
+  // we want round-to-nearest in all cases, irrespective of the rounding mode
-    value = T(pns.mantissa);
+  // selected on the thread.
-    value = value * binary_format<T>::exact_power_of_ten(pns.exponent);
+  // We proceed optimistically, assuming that detail::rounds_to_nearest() returns
-    if (pns.negative) { value = -value; }
+  // true.
-    return answer;
+  if (binary_format<T>::min_exponent_fast_path() <= pns.exponent && pns.exponent <= binary_format<T>::max_exponent_fast_path() && !pns.too_many_digits) {
+    // Unfortunately, the conventional Clinger's fast path is only possible
+    // when the system rounds to the nearest float.
+    //
+    // We expect the next branch to almost always be selected.
+    // We could check it first (before the previous branch), but
+    // there might be performance advantages at having the check
+    // be last.
+    if(detail::rounds_to_nearest())  {
+      // We have that fegetround() == FE_TONEAREST.
+      // Next is Clinger's fast path.
+      if (pns.mantissa <=binary_format<T>::max_mantissa_fast_path()) {
+        value = T(pns.mantissa);
+        if (pns.exponent < 0) { value = value / binary_format<T>::exact_power_of_ten(-pns.exponent); }
+        else { value = value * binary_format<T>::exact_power_of_ten(pns.exponent); }
+        if (pns.negative) { value = -value; }
+        return answer;
+      }
+    } else {
+      // We do not have that fegetround() == FE_TONEAREST.
+      // Next is a modified Clinger's fast path, inspired by Jakub Jelínek's proposal
+      if (pns.exponent >= 0 && pns.mantissa <=binary_format<T>::max_mantissa_fast_path(pns.exponent)) {
+#if (defined(_WIN32) && defined(__clang__))
+        // ClangCL may map 0 to -0.0 when fegetround() == FE_DOWNWARD
+        if(pns.mantissa == 0) {
+          value = 0;
+          return answer;
+        }
+#endif
+        value = T(pns.mantissa) * binary_format<T>::exact_power_of_ten(pns.exponent);
+        if (pns.negative) { value = -value; }
+        return answer;
+      }
+    }
   }
   adjusted_mantissa am = compute_float<binary_format<T>>(pns.exponent, pns.mantissa);
   if(pns.too_many_digits && am.power2 >= 0) {

tests/CMakeLists.txt

@@ -9,7 +9,7 @@ option(SYSTEM_DOCTEST "Use system copy of doctest" OFF)
 if (NOT SYSTEM_DOCTEST)
   FetchContent_Declare(doctest
     GIT_REPOSITORY https://github.com/onqtam/doctest.git
-    GIT_TAG 2.4.6)
+    GIT_TAG v2.4.9)
 endif()
 FetchContent_Declare(supplemental_test_files
   GIT_REPOSITORY https://github.com/fastfloat/supplemental_test_files.git

tests/basictest.cpp

@@ -10,6 +10,7 @@
 #include <limits>
 #include <string>
 #include <system_error>
+#include <cfenv>
 
 #ifndef SUPPLEMENTAL_TEST_DATA_DIR
 #define SUPPLEMENTAL_TEST_DATA_DIR "data/"
@@ -42,6 +43,145 @@
 #define FASTFLOAT_ODDPLATFORM 1
 #endif
 
+
+#define iHexAndDec(v) std::hex << "0x" << (v) << " (" << std::dec << (v) << ")"
+#define fHexAndDec(v) std::hexfloat << (v) << " (" << std::defaultfloat << (v) << ")"
+
+
+const char * round_name(int d) {
+  switch(d) {
+    case FE_UPWARD:
+      return "FE_UPWARD";
+    case FE_DOWNWARD:
+      return "FE_DOWNWARD";
+    case FE_TOWARDZERO:
+      return "FE_TOWARDZERO";
+    case FE_TONEAREST:
+      return "FE_TONEAREST";
+    default:
+      return "UNKNOWN";
+  }
+}
+
+
+#define FASTFLOAT_STR(x)   #x
+#define SHOW_DEFINE(x) printf("%s='%s'\n", #x, FASTFLOAT_STR(x))
+
+TEST_CASE("system_info") {
+    std::cout << "system info:" << std::endl;
+#ifdef _MSC_VER
+    SHOW_DEFINE(_MSC_VER);
+#endif
+#ifdef FASTFLOAT_64BIT_LIMB
+    SHOW_DEFINE(FASTFLOAT_64BIT_LIMB);
+#endif
+#ifdef __clang__
+    SHOW_DEFINE(__clang__);
+#endif
+#ifdef FASTFLOAT_VISUAL_STUDIO
+    SHOW_DEFINE(FASTFLOAT_VISUAL_STUDIO);
+#endif
+#ifdef FASTFLOAT_IS_BIG_ENDIAN
+    #if FASTFLOAT_IS_BIG_ENDIAN
+      printf("big endian\n");
+    #else
+      printf("little endian\n");
+    #endif
+#endif
+#ifdef FASTFLOAT_32BIT
+    SHOW_DEFINE(FASTFLOAT_32BIT);
+#endif
+#ifdef FASTFLOAT_64BIT
+    SHOW_DEFINE(FASTFLOAT_64BIT);
+#endif
+#ifdef FLT_EVAL_METHOD
+    SHOW_DEFINE(FLT_EVAL_METHOD);
+#endif
+#ifdef _WIN32
+    SHOW_DEFINE(_WIN32);
+#endif
+#ifdef _WIN64
+    SHOW_DEFINE(_WIN64);
+#endif
+    std::cout << "fegetround() = " << round_name(fegetround()) << std::endl;
+    std::cout << std::endl;
+
+}
+
+
+TEST_CASE("rounds_to_nearest") {
+  //
+  // If this function fails, we may be left in a non-standard rounding state.
+  //
+  static volatile float fmin = std::numeric_limits<float>::min();
+  fesetround(FE_UPWARD);
+  std::cout << "FE_UPWARD: fmin + 1.0f = " << iHexAndDec(fmin + 1.0f) << " 1.0f - fmin = " << iHexAndDec(1.0f - fmin) << std::endl;
+  CHECK(fegetround() == FE_UPWARD);
+  CHECK(fast_float::detail::rounds_to_nearest() == false);
+
+  fesetround(FE_DOWNWARD);
+  std::cout << "FE_DOWNWARD: fmin + 1.0f = " << iHexAndDec(fmin + 1.0f) << " 1.0f - fmin = " << iHexAndDec(1.0f - fmin) << std::endl;
+  CHECK(fegetround() == FE_DOWNWARD);
+  CHECK(fast_float::detail::rounds_to_nearest() == false);
+
+  fesetround(FE_TOWARDZERO);
+  std::cout << "FE_TOWARDZERO: fmin + 1.0f = " << iHexAndDec(fmin + 1.0f) << " 1.0f - fmin = " << iHexAndDec(1.0f - fmin) << std::endl;
+  CHECK(fegetround() == FE_TOWARDZERO);
+  CHECK(fast_float::detail::rounds_to_nearest() == false);
+
+  fesetround(FE_TONEAREST);
+  std::cout << "FE_TONEAREST: fmin + 1.0f = " << iHexAndDec(fmin + 1.0f) << " 1.0f - fmin = " << iHexAndDec(1.0f - fmin) << std::endl;
+  CHECK(fegetround() == FE_TONEAREST);
+  CHECK(fast_float::detail::rounds_to_nearest() == true);
+}
+
+TEST_CASE("parse_zero") {
+  //
+  // If this function fails, we may be left in a non-standard rounding state.
+  //
+  const char * zero = "0";
+  uint64_t float64_parsed;
+  double f = 0;
+  ::memcpy(&float64_parsed, &f, sizeof(f));
+  CHECK(float64_parsed == 0);
+
+  fesetround(FE_UPWARD);
+  auto r1 = fast_float::from_chars(zero, zero + 1, f);
+  CHECK(r1.ec == std::errc());
+  std::cout << "FE_UPWARD parsed zero as " << iHexAndDec(f) << std::endl;
+  CHECK(f == 0);
+  ::memcpy(&float64_parsed, &f, sizeof(f));
+  std::cout << "double as uint64_t is " << float64_parsed << std::endl;
+  CHECK(float64_parsed == 0);
+
+  fesetround(FE_TOWARDZERO);
+  auto r2 = fast_float::from_chars(zero, zero + 1, f);
+  CHECK(r2.ec == std::errc());
+  std::cout << "FE_TOWARDZERO parsed zero as " << iHexAndDec(f) << std::endl;
+  CHECK(f == 0);
+  ::memcpy(&float64_parsed, &f, sizeof(f));
+  std::cout << "double as uint64_t is " << float64_parsed << std::endl;
+  CHECK(float64_parsed == 0);
+
+  fesetround(FE_DOWNWARD);
+  auto r3 = fast_float::from_chars(zero, zero + 1, f);
+  CHECK(r3.ec == std::errc());
+  std::cout << "FE_DOWNWARD parsed zero as " << iHexAndDec(f) << std::endl;
+  CHECK(f == 0);
+  ::memcpy(&float64_parsed, &f, sizeof(f));
+  std::cout << "double as uint64_t is " << float64_parsed << std::endl;
+  CHECK(float64_parsed == 0);
+
+  fesetround(FE_TONEAREST);
+  auto r4 = fast_float::from_chars(zero, zero + 1, f);
+  CHECK(r4.ec == std::errc());
+  std::cout << "FE_TONEAREST parsed zero as " << iHexAndDec(f) << std::endl;
+  CHECK(f == 0);
+  ::memcpy(&float64_parsed, &f, sizeof(f));
+  std::cout << "double as uint64_t is " << float64_parsed << std::endl;
+  CHECK(float64_parsed == 0);
+}
+
 // C++ 17 because it is otherwise annoying to browse all files in a directory.
 // We also only run these tests on little endian systems.
 #if (FASTFLOAT_CPLUSPLUS >= 201703L) && (FASTFLOAT_IS_BIG_ENDIAN == 0) && !defined(FASTFLOAT_ODDPLATFORM)
@@ -50,59 +190,77 @@
 #include <filesystem>
 #include <charconv>
 
+
+
 // return true on success
 bool check_file(std::string file_name) {
   std::cout << "Checking " << file_name << std::endl;
-  size_t number{0};
+  // We check all rounding directions, for each file.
-  std::fstream newfile(file_name, std::ios::in);
+  std::vector<int> directions = {FE_UPWARD, FE_DOWNWARD, FE_TOWARDZERO, FE_TONEAREST};
-  if (newfile.is_open()) {
+  for (int d : directions) {
-    std::string str;
+    std::cout << "fesetround to " << round_name(d) << std::endl;
-    while (std::getline(newfile, str)) {
+    fesetround(d);
-      if (str.size() > 0) {
+    size_t number{0};
-        // Read 32-bit hex
+    std::fstream newfile(file_name, std::ios::in);
-        uint32_t float32;
+    if (newfile.is_open()) {
-        auto r32 = std::from_chars(str.data() + 5, str.data() + str.size(),
+      std::string str;
+      while (std::getline(newfile, str)) {
+        if (str.size() > 0) {
+          // Read 32-bit hex
+          uint32_t float32;
+          auto r32 = std::from_chars(str.data() + 5, str.data() + str.size(),
                                    float32, 16);
-        if(r32.ec != std::errc()) { std::cerr << "32-bit parsing failure\n"; return false; }
+          if(r32.ec != std::errc()) { std::cerr << "32-bit parsing failure\n"; return false; }
-        // Read 64-bit hex
+          // Read 64-bit hex
-        uint64_t float64;
+          uint64_t float64;
-        auto r64 = std::from_chars(str.data() + 14, str.data() + str.size(),
+          auto r64 = std::from_chars(str.data() + 14, str.data() + str.size(),
                                    float64, 16);
-        if(r64.ec != std::errc()) { std::cerr << "64-bit parsing failure\n"; return false; }
+          if(r64.ec != std::errc()) { std::cerr << "64-bit parsing failure\n"; return false; }
-        // The string to parse:
+          // The string to parse:
-        const char *number_string = str.data() + 31;
+          const char *number_string = str.data() + 31;
-        const char *end_of_string = str.data() + str.size();
+          const char *end_of_string = str.data() + str.size();
-        // Parse as 32-bit float
+          // Parse as 32-bit float
-        float parsed_32;
+          float parsed_32;
-        auto fast_float_r32 = fast_float::from_chars(number_string, end_of_string, parsed_32);
+          auto fast_float_r32 = fast_float::from_chars(number_string, end_of_string, parsed_32);
-        if(fast_float_r32.ec != std::errc()) { std::cerr << "parsing failure\n"; return false; }
+          if(fast_float_r32.ec != std::errc()) { std::cerr << "parsing failure\n"; return false; }
-        // Parse as 64-bit float
+          // Parse as 64-bit float
-        double parsed_64;
+          double parsed_64;
-        auto fast_float_r64 = fast_float::from_chars(number_string, end_of_string, parsed_64);
+          auto fast_float_r64 = fast_float::from_chars(number_string, end_of_string, parsed_64);
-        if(fast_float_r64.ec != std::errc()) { std::cerr << "parsing failure\n"; return false; }
+          if(fast_float_r64.ec != std::errc()) { std::cerr << "parsing failure\n"; return false; }
-        // Convert the floats to unsigned ints.
+          // Convert the floats to unsigned ints.
-        uint32_t float32_parsed;
+          uint32_t float32_parsed;
-        uint64_t float64_parsed;
+          uint64_t float64_parsed;
-        ::memcpy(&float32_parsed, &parsed_32, sizeof(parsed_32));
+          ::memcpy(&float32_parsed, &parsed_32, sizeof(parsed_32));
-        ::memcpy(&float64_parsed, &parsed_64, sizeof(parsed_64));
+          ::memcpy(&float64_parsed, &parsed_64, sizeof(parsed_64));
-        // Compare with expected results
+          // Compare with expected results
-        if (float32_parsed != float32) {
+          if (float32_parsed != float32) {
-          std::cout << "bad 32 " << str << std::endl;
+            std::cout << "bad 32 " << str << std::endl;
-          return false;
+            std::cout << "parsed as " << iHexAndDec(parsed_32) << std::endl;
+            std::cout << "as  raw uint32_t, parsed = " << float32_parsed << ", expected = " << float32 << std::endl;
+            std::cout << "fesetround: " << round_name(d) << std::endl;
+            fesetround(FE_TONEAREST);
+            return false;
+          }
+          if (float64_parsed != float64) {
+            std::cout << "bad 64 " << str << std::endl;
+            std::cout << "parsed as " << iHexAndDec(parsed_64) << std::endl;
+            std::cout << "as raw uint64_t, parsed = " << float64_parsed << ", expected = " << float64 << std::endl;
+            std::cout << "fesetround: " << round_name(d) << std::endl;
+            fesetround(FE_TONEAREST);
+            return false;
+          }
+          number++;
         }
-        if (float64_parsed != float64) {
-          std::cout << "bad 64 " << str << std::endl;
-          return false;
-        }
-        number++;
       }
+      std::cout << "checked " << std::defaultfloat << number << " values" << std::endl;
+      newfile.close(); // close the file object
+    } else {
+      std::cout << "Could not read  " << file_name << std::endl;
+      fesetround(FE_TONEAREST);
+      return false;
     }
-    std::cout << "checked " << std::defaultfloat << number << " values" << std::endl;
-    newfile.close(); // close the file object
-  } else {
-    std::cout << "Could not read  " << file_name << std::endl;
-    return false;
   }
+  fesetround(FE_TONEAREST);
   return true;
 }
 
@@ -125,9 +283,6 @@ TEST_CASE("leading_zeroes") {
   CHECK(fast_float::leading_zeroes(bit << 63) ==  0);
 }
 
-#define iHexAndDec(v) std::hex << "0x" << (v) << " (" << std::dec << (v) << ")"
-#define fHexAndDec(v) std::hexfloat << (v) << " (" << std::defaultfloat << (v) << ")"
-
 void test_full_multiplication(uint64_t lhs, uint64_t rhs, uint64_t expected_lo, uint64_t expected_hi) {
   fast_float::value128 v;
   v = fast_float::full_multiplication(lhs, rhs);