16-bit float support

include/fast_float/float_common.h

@@ -221,13 +221,19 @@ fastfloat_really_inline constexpr bool cpp20_and_in_constexpr() {
 
 template <typename T>
 struct is_supported_float_type
-    : std::integral_constant<bool, std::is_same<T, float>::value ||
-                                       std::is_same<T, double>::value
+    : std::integral_constant<
+          bool, std::is_same<T, float>::value || std::is_same<T, double>::value
 #ifdef __STDCPP_FLOAT32_T__
                     || std::is_same<T, std::float32_t>::value
 #endif
 #ifdef __STDCPP_FLOAT64_T__
                     || std::is_same<T, std::float64_t>::value
+#endif
+#ifdef __STDCPP_FLOAT16_T__
+                    || std::is_same<T, std::float16_t>::value
+#endif
+#ifdef __STDCPP_BFLOAT16_T__
+                    || std::is_same<T, std::bfloat16_t>::value
 #endif
           > {
 };
@@ -622,6 +628,157 @@ inline constexpr uint64_t binary_format<double>::max_mantissa_fast_path() {
   return uint64_t(2) << mantissa_explicit_bits();
 }
 
+// credit: Jakub Jelínek
+#ifdef __STDCPP_FLOAT16_T__
+
+template <typename U> struct binary_format_lookup_tables<std::float16_t, U> {
+  static constexpr std::float16_t powers_of_ten[] = {};
+  static constexpr uint64_t max_mantissa[] = {};
+};
+
+template <typename U>
+constexpr std::float16_t
+    binary_format_lookup_tables<std::float16_t, U>::powers_of_ten[];
+
+template <typename U>
+constexpr uint64_t
+    binary_format_lookup_tables<std::float16_t, U>::max_mantissa[];
+
+template <>
+inline constexpr int binary_format<std::float16_t>::max_exponent_fast_path() {
+  return 0;
+}
+
+template <>
+inline constexpr uint64_t
+binary_format<std::float16_t>::max_mantissa_fast_path() {
+  return 0;
+}
+
+template <>
+inline constexpr int binary_format<std::float16_t>::min_exponent_fast_path() {
+  return 0;
+}
+
+template <>
+constexpr int binary_format<std::float16_t>::mantissa_explicit_bits() {
+  return 10;
+}
+
+template <>
+constexpr int binary_format<std::float16_t>::max_exponent_round_to_even() {
+  return 5;
+}
+
+template <>
+constexpr int binary_format<std::float16_t>::min_exponent_round_to_even() {
+  return -22;
+}
+
+template <> constexpr int binary_format<std::float16_t>::minimum_exponent() {
+  return -15;
+}
+
+template <> constexpr int binary_format<std::float16_t>::infinite_power() {
+  return 0x1F;
+}
+
+template <> constexpr int binary_format<std::float16_t>::sign_index() {
+  return 15;
+}
+
+template <>
+constexpr int binary_format<std::float16_t>::largest_power_of_ten() {
+  return 4;
+}
+
+template <>
+constexpr int binary_format<std::float16_t>::smallest_power_of_ten() {
+  return -27;
+}
+
+template <> constexpr size_t binary_format<std::float16_t>::max_digits() {
+  return 22;
+}
+
+#endif
+
+// credit: Jakub Jelínek
+#ifdef __STDCPP_BFLOAT16_T__
+
+template <typename U> struct binary_format_lookup_tables<std::bfloat16_t, U> {
+  static constexpr std::bfloat16_t powers_of_ten[] = {};
+
+  static constexpr uint64_t max_mantissa[] = {};
+};
+
+template <typename U>
+constexpr std::bfloat16_t
+    binary_format_lookup_tables<std::bfloat16_t, U>::powers_of_ten[];
+
+template <typename U>
+constexpr uint64_t
+    binary_format_lookup_tables<std::bfloat16_t, U>::max_mantissa[];
+
+template <>
+inline constexpr int binary_format<std::bfloat16_t>::max_exponent_fast_path() {
+  return 0;
+}
+
+template <>
+inline constexpr uint64_t
+binary_format<std::bfloat16_t>::max_mantissa_fast_path() {
+  return 0;
+}
+
+template <>
+inline constexpr int binary_format<std::bfloat16_t>::min_exponent_fast_path() {
+  return 0;
+}
+
+template <>
+constexpr int binary_format<std::bfloat16_t>::mantissa_explicit_bits() {
+  return 7;
+}
+
+template <>
+constexpr int binary_format<std::bfloat16_t>::max_exponent_round_to_even() {
+  return 3;
+}
+
+template <>
+constexpr int binary_format<std::bfloat16_t>::min_exponent_round_to_even() {
+  return -24;
+}
+
+template <> constexpr int binary_format<std::bfloat16_t>::minimum_exponent() {
+  return -127;
+}
+
+template <> constexpr int binary_format<std::bfloat16_t>::infinite_power() {
+  return 0xFF;
+}
+
+template <> constexpr int binary_format<std::bfloat16_t>::sign_index() {
+  return 15;
+}
+
+template <>
+constexpr int binary_format<std::bfloat16_t>::largest_power_of_ten() {
+  return 38;
+}
+
+template <>
+constexpr int binary_format<std::bfloat16_t>::smallest_power_of_ten() {
+  return -60;
+}
+
+template <> constexpr size_t binary_format<std::bfloat16_t>::max_digits() {
+  return 98;
+}
+
+#endif
+
 template <>
 inline constexpr uint64_t
 binary_format<double>::max_mantissa_fast_path(int64_t power) {

tests/basictest.cpp

@@ -275,6 +275,16 @@ bool check_file(std::string file_name) {
       std::string str;
       while (std::getline(newfile, str)) {
         if (str.size() > 0) {
+#ifdef __STDCPP_FLOAT16_T__
+          // Read 16-bit hex
+          uint16_t float16;
+          auto r16 =
+              std::from_chars(str.data(), str.data() + str.size(), float16, 16);
+          if (r16.ec != std::errc()) {
+            std::cerr << "16-bit parsing failure\n";
+            return false;
+          }
+#endif
           // Read 32-bit hex
           uint32_t float32;
           auto r32 = std::from_chars(str.data() + 5, str.data() + str.size(),
@@ -294,6 +304,17 @@ bool check_file(std::string file_name) {
           // The string to parse:
           char const *number_string = str.data() + 31;
           char const *end_of_string = str.data() + str.size();
+#ifdef __STDCPP_FLOAT16_T__
+          // Parse as 16-bit float
+          std::float16_t parsed_16{};
+          // auto fast_float_r16 =
+          fast_float::from_chars(number_string, end_of_string, parsed_16);
+          // if (fast_float_r16.ec != std::errc() &&
+          //   fast_float_r16.ec != std::errc::result_out_of_range) {
+          // std::cerr << "16-bit fast_float parsing failure for: " + str +
+          // "\n"; return false;
+          // }
+#endif
           // Parse as 32-bit float
           float parsed_32;
           auto fast_float_r32 =
@@ -313,11 +334,29 @@ bool check_file(std::string file_name) {
             return false;
           }
           // Convert the floats to unsigned ints.
+#ifdef __STDCPP_FLOAT16_T__
+          uint16_t float16_parsed;
+#endif
           uint32_t float32_parsed;
           uint64_t float64_parsed;
+#ifdef __STDCPP_FLOAT16_T__
+          ::memcpy(&float16_parsed, &parsed_16, sizeof(parsed_16));
+
+#endif
           ::memcpy(&float32_parsed, &parsed_32, sizeof(parsed_32));
           ::memcpy(&float64_parsed, &parsed_64, sizeof(parsed_64));
           // Compare with expected results
+#ifdef __STDCPP_FLOAT16_T__
+          if (float16_parsed != float16) {
+            std::cout << "bad 16 " << str << std::endl;
+            std::cout << "parsed as " << iHexAndDec(parsed_16) << std::endl;
+            std::cout << "as  raw uint16_t, parsed = " << float16_parsed
+                      << ", expected = " << float16 << std::endl;
+            std::cout << "fesetround: " << round_name(d) << std::endl;
+            fesetround(FE_TONEAREST);
+            return false;
+          }
+#endif
           if (float32_parsed != float32) {
             std::cout << "bad 32 " << str << std::endl;
             std::cout << "parsed as " << iHexAndDec(parsed_32) << std::endl;

tests/example_test.cpp

@@ -112,7 +112,7 @@ bool large() {
 }
 
 int main() {
-  std::string const input = "3.1416 xyz ";
+  std::string input = "3.1416 xyz ";
   double result;
   auto answer =
       fast_float::from_chars(input.data(), input.data() + input.size(), result);
@@ -121,6 +121,19 @@ int main() {
     return EXIT_FAILURE;
   }
   std::cout << "parsed the number " << result << std::endl;
+#ifdef __STDCPP_FLOAT16_T__
+  // Parse as 16-bit float
+  std::float16_t parsed_16{};
+  input = "10000e-1452";
+  auto fast_float_r16 = fast_float::from_chars(
+      input.data(), input.data() + input.size(), parsed_16);
+  if (fast_float_r16.ec != std::errc() &&
+      fast_float_r16.ec != std::errc::result_out_of_range) {
+    std::cerr << "16-bit fast_float parsing failure for: " + input + "\n";
+    return false;
+  }
+  std::cout << "parsed the 16-bit value " << float(parsed_16) << std::endl;
+#endif
   if (!small()) {
     printf("Bug\n");
     return EXIT_FAILURE;