Make dragonbox::to_decimal available in format.h

include/fmt/format-inl.h

@@ -1776,67 +1776,6 @@ inline int floor_log10_pow2_minus_log10_4_over_3(int e) FMT_NOEXCEPT {
          shift_amount;
 }
 
-// Type-specific information that Dragonbox uses.
-template <class T> struct float_info;
-
-template <> struct float_info<float> {
-  using carrier_uint = uint32_t;
-  static const int significand_bits = 23;
-  static const int exponent_bits = 8;
-  static const int min_exponent = -126;
-  static const int max_exponent = 127;
-  static const int exponent_bias = -127;
-  static const int decimal_digits = 9;
-  static const int kappa = 1;
-  static const int big_divisor = 100;
-  static const int small_divisor = 10;
-  static const int min_k = -31;
-  static const int max_k = 46;
-  static const int cache_bits = 64;
-  static const int divisibility_check_by_5_threshold = 39;
-  static const int case_fc_pm_half_lower_threshold = -1;
-  static const int case_fc_pm_half_upper_threshold = 6;
-  static const int case_fc_lower_threshold = -2;
-  static const int case_fc_upper_threshold = 6;
-  static const int case_shorter_interval_left_endpoint_lower_threshold = 2;
-  static const int case_shorter_interval_left_endpoint_upper_threshold = 3;
-  static const int shorter_interval_tie_lower_threshold = -35;
-  static const int shorter_interval_tie_upper_threshold = -35;
-  static const int max_trailing_zeros = 7;
-};
-
-template <> struct float_info<double> {
-  using carrier_uint = uint64_t;
-  static const int significand_bits = 52;
-  static const int exponent_bits = 11;
-  static const int min_exponent = -1022;
-  static const int max_exponent = 1023;
-  static const int exponent_bias = -1023;
-  static const int decimal_digits = 17;
-  static const int kappa = 2;
-  static const int big_divisor = 1000;
-  static const int small_divisor = 100;
-  static const int min_k = -292;
-  static const int max_k = 326;
-  static const int cache_bits = 128;
-  static const int divisibility_check_by_5_threshold = 86;
-  static const int case_fc_pm_half_lower_threshold = -2;
-  static const int case_fc_pm_half_upper_threshold = 9;
-  static const int case_fc_lower_threshold = -4;
-  static const int case_fc_upper_threshold = 9;
-  static const int case_shorter_interval_left_endpoint_lower_threshold = 2;
-  static const int case_shorter_interval_left_endpoint_upper_threshold = 3;
-  static const int shorter_interval_tie_lower_threshold = -77;
-  static const int shorter_interval_tie_upper_threshold = -77;
-  static const int max_trailing_zeros = 16;
-};
-
-template <class T> struct decimal_fp {
-  using significand_type = typename float_info<T>::carrier_uint;
-  significand_type significand;
-  int exponent;
-};
-
 // Returns true iff x is divisible by pow(2, exp).
 inline bool divisible_by_power_of_2(uint32_t x, int exp) FMT_NOEXCEPT {
   FMT_ASSERT(exp >= 1, "");
@@ -2291,7 +2230,9 @@ FMT_ALWAYS_INLINE FMT_SAFEBUFFERS decimal_fp<T> shorter_interval_case(
   return ret_value;
 }
 
-template <class T> FMT_SAFEBUFFERS decimal_fp<T> to_decimal(T x) FMT_NOEXCEPT {
+template <typename T>
+FMT_SAFEBUFFERS enable_if_t<is_fast_float<T>(), decimal_fp<T>> to_decimal(T x)
+    FMT_NOEXCEPT {
   // Step 1: integer promotion & Schubfach multiplier calculation.
 
   using carrier_uint = typename float_info<T>::carrier_uint;

include/fmt/format.h

@@ -587,13 +587,8 @@ inline counting_iterator copy_str(InputIt begin, InputIt end,
   return it + (end - begin);
 }
 
-#ifndef FMT_USE_GRISU
-#  define FMT_USE_GRISU 1
-#endif
-
-template <typename T> constexpr bool use_grisu() {
-  return FMT_USE_GRISU && std::numeric_limits<double>::is_iec559 &&
-         sizeof(T) <= sizeof(double);
+template <typename T> constexpr bool is_fast_float() {
+  return std::numeric_limits<T>::is_iec559 && sizeof(T) <= sizeof(double);
 }
 
 #ifndef FMT_USE_FULL_CACHE_DRAGONBOX
@@ -1368,6 +1363,78 @@ int snprintf_float(T value, int precision, float_specs specs,
 template <typename T> T promote_float(T value) { return value; }
 inline double promote_float(float value) { return static_cast<double>(value); }
 
+namespace dragonbox {
+
+// Type-specific information that Dragonbox uses.
+template <class T> struct float_info;
+
+template <> struct float_info<float> {
+  using carrier_uint = uint32_t;
+  static const int significand_bits = 23;
+  static const int exponent_bits = 8;
+  static const int min_exponent = -126;
+  static const int max_exponent = 127;
+  static const int exponent_bias = -127;
+  static const int decimal_digits = 9;
+  static const int kappa = 1;
+  static const int big_divisor = 100;
+  static const int small_divisor = 10;
+  static const int min_k = -31;
+  static const int max_k = 46;
+  static const int cache_bits = 64;
+  static const int divisibility_check_by_5_threshold = 39;
+  static const int case_fc_pm_half_lower_threshold = -1;
+  static const int case_fc_pm_half_upper_threshold = 6;
+  static const int case_fc_lower_threshold = -2;
+  static const int case_fc_upper_threshold = 6;
+  static const int case_shorter_interval_left_endpoint_lower_threshold = 2;
+  static const int case_shorter_interval_left_endpoint_upper_threshold = 3;
+  static const int shorter_interval_tie_lower_threshold = -35;
+  static const int shorter_interval_tie_upper_threshold = -35;
+  static const int max_trailing_zeros = 7;
+};
+
+template <> struct float_info<double> {
+  using carrier_uint = uint64_t;
+  static const int significand_bits = 52;
+  static const int exponent_bits = 11;
+  static const int min_exponent = -1022;
+  static const int max_exponent = 1023;
+  static const int exponent_bias = -1023;
+  static const int decimal_digits = 17;
+  static const int kappa = 2;
+  static const int big_divisor = 1000;
+  static const int small_divisor = 100;
+  static const int min_k = -292;
+  static const int max_k = 326;
+  static const int cache_bits = 128;
+  static const int divisibility_check_by_5_threshold = 86;
+  static const int case_fc_pm_half_lower_threshold = -2;
+  static const int case_fc_pm_half_upper_threshold = 9;
+  static const int case_fc_lower_threshold = -4;
+  static const int case_fc_upper_threshold = 9;
+  static const int case_shorter_interval_left_endpoint_lower_threshold = 2;
+  static const int case_shorter_interval_left_endpoint_upper_threshold = 3;
+  static const int shorter_interval_tie_lower_threshold = -77;
+  static const int shorter_interval_tie_upper_threshold = -77;
+  static const int max_trailing_zeros = 16;
+};
+
+template <typename T> struct decimal_fp {
+  using significand_type = typename float_info<T>::carrier_uint;
+  significand_type significand;
+  int exponent;
+};
+
+template <typename T>
+enable_if_t<is_fast_float<T>(), decimal_fp<T>> to_decimal(T x) FMT_NOEXCEPT;
+
+template <typename T>
+inline enable_if_t<!is_fast_float<T>(), unformattable> to_decimal(T) {
+  return {};
+}
+}  // namespace dragonbox
+
 template <typename Handler>
 FMT_CONSTEXPR void handle_int_type_spec(char spec, Handler&& handler) {
   switch (spec) {
@@ -1810,7 +1877,7 @@ OutputIt write(OutputIt out, T value, basic_format_specs<Char> specs,
       ++precision;
   }
   if (const_check(std::is_same<T, float>())) fspecs.binary32 = true;
-  fspecs.use_grisu = use_grisu<T>();
+  fspecs.use_grisu = is_fast_float<T>();
   int exp = format_float(promote_float(value), precision, fspecs, buffer);
   fspecs.precision = precision;
   Char point =
@@ -1837,7 +1904,7 @@ OutputIt write(OutputIt out, T value) {
   memory_buffer buffer;
   int precision = -1;
   if (const_check(std::is_same<T, float>())) fspecs.binary32 = true;
-  fspecs.use_grisu = use_grisu<T>();
+  fspecs.use_grisu = is_fast_float<T>();
   int exp = format_float(promote_float(value), precision, fspecs, buffer);
   fspecs.precision = precision;
   float_writer<Char> w(buffer.data(), static_cast<int>(buffer.size()), exp,