Merge branch 'main' into dlemire/adding_more_cxx20_in_ci

.github/workflows/vs17-cxx20.yml

@@ -18,8 +18,12 @@ jobs:
       - name: checkout
         uses: actions/checkout@v3
       - name: configure
-        run: |
+        run: >-
-          cmake -S . -B build -G "${{matrix.gen}}" -A ${{matrix.arch}}  -DCMAKE_CXX_STANDARD=20 -DFASTFLOAT_TEST=ON -DCMAKE_INSTALL_PREFIX:PATH=destination ..
+          cmake -S . -B build -G "${{matrix.gen}}" -A ${{matrix.arch}}
+          -DCMAKE_CXX_STANDARD=20
+          -DFASTFLOAT_TEST=ON
+          -DFASTFLOAT_CONSTEXPR_TESTS=ON
+          -DCMAKE_INSTALL_PREFIX:PATH=destination
       - name: build
         run: |
           cmake --build build --verbose --config ${{matrix.cfg}} --parallel

include/fast_float/ascii_number.h

@@ -27,7 +27,16 @@ fastfloat_really_inline constexpr uint64_t byteswap(uint64_t val) {
     | (val & 0x00000000000000FF) << 56;
 }
 
-fastfloat_really_inline uint64_t read_u64(const char *chars) {
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
+uint64_t read_u64(const char *chars) {
+  if (cpp20_and_in_constexpr()) {
+    uint64_t val = 0;
+    for(int i = 0; i < 8; ++i) {
+      val |= uint64_t(*chars) << (i*8);
+      ++chars;
+    }
+    return val;
+  }
   uint64_t val;
   ::memcpy(&val, chars, sizeof(uint64_t));
 #if FASTFLOAT_IS_BIG_ENDIAN == 1
@@ -37,7 +46,16 @@ fastfloat_really_inline uint64_t read_u64(const char *chars) {
   return val;
 }
 
-fastfloat_really_inline void write_u64(uint8_t *chars, uint64_t val) {
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
+void write_u64(uint8_t *chars, uint64_t val) {
+  if (cpp20_and_in_constexpr()) {
+    for(int i = 0; i < 8; ++i) {
+      *chars = uint8_t(val);
+      val >>= 8;
+      ++chars;
+    }
+    return;
+  }
 #if FASTFLOAT_IS_BIG_ENDIAN == 1
   // Need to read as-if the number was in little-endian order.
   val = byteswap(val);
@@ -57,7 +75,8 @@ uint32_t parse_eight_digits_unrolled(uint64_t val) {
   return uint32_t(val);
 }
 
-fastfloat_really_inline uint32_t parse_eight_digits_unrolled(const char *chars)  noexcept  {
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
+uint32_t parse_eight_digits_unrolled(const char *chars)  noexcept  {
   return parse_eight_digits_unrolled(read_u64(chars));
 }
 
@@ -67,7 +86,8 @@ fastfloat_really_inline constexpr bool is_made_of_eight_digits_fast(uint64_t val
      0x8080808080808080));
 }
 
-fastfloat_really_inline bool is_made_of_eight_digits_fast(const char *chars)  noexcept  {
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
+bool is_made_of_eight_digits_fast(const char *chars)  noexcept  {
   return is_made_of_eight_digits_fast(read_u64(chars));
 }
 
@@ -87,7 +107,7 @@ struct parsed_number_string {
 
 // Assuming that you use no more than 19 digits, this will
 // parse an ASCII string.
-fastfloat_really_inline
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
 parsed_number_string parse_number_string(const char *p, const char *pend, parse_options options) noexcept {
   const chars_format fmt = options.format;
   const char decimal_point = options.decimal_point;

include/fast_float/bigint.h

@@ -514,7 +514,7 @@ struct bigint : pow5_tables<> {
       // move limbs
       limb* dst = vec.data + n;
       const limb* src = vec.data;
-      ::memmove(dst, src, sizeof(limb) * vec.len());
+      std::copy_backward(src, src + vec.len(), dst + vec.len());
       // fill in empty limbs
       limb* first = vec.data;
       limb* last = first + n;
@@ -594,7 +594,12 @@ struct bigint : pow5_tables<> {
       exp -= small_step;
     }
     if (exp != 0) {
-      FASTFLOAT_TRY(small_mul(vec, limb(small_power_of_5[exp])));
+      // Work around clang bug https://godbolt.org/z/zedh7rrhc
+      // This is similar to https://github.com/llvm/llvm-project/issues/47746,
+      // except the workaround described there don't work here
+      FASTFLOAT_TRY(
+        small_mul(vec, limb(((void)small_power_of_5[0], small_power_of_5[exp])))
+      );
     }
 
     return true;

include/fast_float/constexpr_feature_detect.h

@@ -0,0 +1,40 @@
+#ifndef FASTFLOAT_CONSTEXPR_FEATURE_DETECT_H
+#define FASTFLOAT_CONSTEXPR_FEATURE_DETECT_H
+
+#ifdef __has_include
+#if __has_include(<version>)
+#include <version>
+#endif
+#endif
+
+// Testing for https://wg21.link/N3652, adopted in C++14
+#if __cpp_constexpr >= 201304
+#define FASTFLOAT_CONSTEXPR14 constexpr
+#else
+#define FASTFLOAT_CONSTEXPR14
+#endif
+
+#if __cpp_lib_bit_cast >= 201806L
+#define FASTFLOAT_HAS_BIT_CAST 1
+#else
+#define FASTFLOAT_HAS_BIT_CAST 0
+#endif
+
+#if __cpp_lib_is_constant_evaluated >= 201811L
+#define FASTFLOAT_HAS_IS_CONSTANT_EVALUATED 1
+#else
+#define FASTFLOAT_HAS_IS_CONSTANT_EVALUATED 0
+#endif
+
+// Testing for relevant C++20 constexpr library features
+#if FASTFLOAT_HAS_IS_CONSTANT_EVALUATED \
+    && FASTFLOAT_HAS_BIT_CAST \
+    && __cpp_lib_constexpr_algorithms >= 201806L /*For std::copy and std::fill*/
+#define FASTFLOAT_CONSTEXPR20 constexpr
+#define FASTFLOAT_IS_CONSTEXPR 1
+#else
+#define FASTFLOAT_CONSTEXPR20
+#define FASTFLOAT_IS_CONSTEXPR 0
+#endif
+
+#endif // FASTFLOAT_CONSTEXPR_FEATURE_DETECT_H

include/fast_float/decimal_to_binary.h

@@ -17,7 +17,7 @@ namespace fast_float {
 // low part corresponding to the least significant bits.
 //
 template <int bit_precision>
-fastfloat_really_inline
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
 value128 compute_product_approximation(int64_t q, uint64_t w) {
   const int index = 2 * int(q - powers::smallest_power_of_five);
   // For small values of q, e.g., q in [0,27], the answer is always exact because
@@ -76,7 +76,7 @@ adjusted_mantissa compute_error_scaled(int64_t q, uint64_t w, int lz) noexcept
 // w * 10 ** q, without rounding the representation up.
 // the power2 in the exponent will be adjusted by invalid_am_bias.
 template <typename binary>
-fastfloat_really_inline
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
 adjusted_mantissa compute_error(int64_t q, uint64_t w)  noexcept  {
   int lz = leading_zeroes(w);
   w <<= lz;
@@ -90,7 +90,7 @@ adjusted_mantissa compute_error(int64_t q, uint64_t w)  noexcept  {
 // return an adjusted_mantissa with a negative power of 2: the caller should recompute
 // in such cases.
 template <typename binary>
-fastfloat_really_inline
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
 adjusted_mantissa compute_float(int64_t q, uint64_t w)  noexcept  {
   adjusted_mantissa answer;
   if ((w == 0) || (q < binary::smallest_power_of_ten())) {

include/fast_float/digit_comparison.h

@@ -44,7 +44,8 @@ int32_t scientific_exponent(parsed_number_string& num) noexcept {
 
 // this converts a native floating-point number to an extended-precision float.
 template <typename T>
-fastfloat_really_inline adjusted_mantissa to_extended(T value) noexcept {
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
+adjusted_mantissa to_extended(T value) noexcept {
   using equiv_uint = typename binary_format<T>::equiv_uint;
   constexpr equiv_uint exponent_mask = binary_format<T>::exponent_mask();
   constexpr equiv_uint mantissa_mask = binary_format<T>::mantissa_mask();
@@ -53,7 +54,11 @@ fastfloat_really_inline adjusted_mantissa to_extended(T value) noexcept {
   adjusted_mantissa am;
   int32_t bias = binary_format<T>::mantissa_explicit_bits() - binary_format<T>::minimum_exponent();
   equiv_uint bits;
+#if FASTFLOAT_HAS_BIT_CAST
+  bits = std::bit_cast<equiv_uint>(value);
+#else
   ::memcpy(&bits, &value, sizeof(T));
+#endif
   if ((bits & exponent_mask) == 0) {
     // denormal
     am.power2 = 1 - bias;
@@ -72,7 +77,8 @@ fastfloat_really_inline adjusted_mantissa to_extended(T value) noexcept {
 // we are given a native float that represents b, so we need to adjust it
 // halfway between b and b+u.
 template <typename T>
-fastfloat_really_inline adjusted_mantissa to_extended_halfway(T value) noexcept {
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
+adjusted_mantissa to_extended_halfway(T value) noexcept {
   adjusted_mantissa am = to_extended(value);
   am.mantissa <<= 1;
   am.mantissa += 1;
@@ -148,9 +154,10 @@ void round_down(adjusted_mantissa& am, int32_t shift) noexcept {
   am.power2 += shift;
 }
 
-fastfloat_really_inline void skip_zeros(const char*& first, const char* last) noexcept {
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
+void skip_zeros(const char*& first, const char* last) noexcept {
   uint64_t val;
-  while (std::distance(first, last) >= 8) {
+  while (!cpp20_and_in_constexpr() && std::distance(first, last) >= 8) {
     ::memcpy(&val, first, sizeof(uint64_t));
     if (val != 0x3030303030303030) {
       break;
@@ -167,10 +174,11 @@ fastfloat_really_inline void skip_zeros(const char*& first, const char* last) no
 
 // determine if any non-zero digits were truncated.
 // all characters must be valid digits.
-fastfloat_really_inline bool is_truncated(const char* first, const char* last) noexcept {
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
+bool is_truncated(const char* first, const char* last) noexcept {
   // do 8-bit optimizations, can just compare to 8 literal 0s.
   uint64_t val;
-  while (std::distance(first, last) >= 8) {
+  while (!cpp20_and_in_constexpr() && std::distance(first, last) >= 8) {
     ::memcpy(&val, first, sizeof(uint64_t));
     if (val != 0x3030303030303030) {
       return true;
@@ -186,11 +194,12 @@ fastfloat_really_inline bool is_truncated(const char* first, const char* last) n
   return false;
 }
 
-fastfloat_really_inline bool is_truncated(byte_span s) noexcept {
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
+bool is_truncated(byte_span s) noexcept {
   return is_truncated(s.ptr, s.ptr + s.len());
 }
 
-fastfloat_really_inline
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
 void parse_eight_digits(const char*& p, limb& value, size_t& counter, size_t& count) noexcept {
   value = value * 100000000 + parse_eight_digits_unrolled(p);
   p += 8;
@@ -206,13 +215,14 @@ void parse_one_digit(const char*& p, limb& value, size_t& counter, size_t& count
   count++;
 }
 
-fastfloat_really_inline
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
 void add_native(bigint& big, limb power, limb value) noexcept {
   big.mul(power);
   big.add(value);
 }
 
-fastfloat_really_inline void round_up_bigint(bigint& big, size_t& count) noexcept {
+fastfloat_really_inline FASTFLOAT_CONSTEXPR20
+void round_up_bigint(bigint& big, size_t& count) noexcept {
   // need to round-up the digits, but need to avoid rounding
   // ....9999 to ...10000, which could cause a false halfway point.
   add_native(big, 10, 1);
@@ -220,7 +230,8 @@ fastfloat_really_inline void round_up_bigint(bigint& big, size_t& count) noexcep
 }
 
 // parse the significant digits into a big integer
-inline void parse_mantissa(bigint& result, parsed_number_string& num, size_t max_digits, size_t& digits) noexcept {
+inline FASTFLOAT_CONSTEXPR20
+void parse_mantissa(bigint& result, parsed_number_string& num, size_t max_digits, size_t& digits) noexcept {
   // try to minimize the number of big integer and scalar multiplication.
   // therefore, try to parse 8 digits at a time, and multiply by the largest
   // scalar value (9 or 19 digits) for each step.
@@ -300,7 +311,8 @@ inline void parse_mantissa(bigint& result, parsed_number_string& num, size_t max
 }
 
 template <typename T>
-inline adjusted_mantissa positive_digit_comp(bigint& bigmant, int32_t exponent) noexcept {
+inline FASTFLOAT_CONSTEXPR20
+adjusted_mantissa positive_digit_comp(bigint& bigmant, int32_t exponent) noexcept {
   FASTFLOAT_ASSERT(bigmant.pow10(uint32_t(exponent)));
   adjusted_mantissa answer;
   bool truncated;
@@ -323,7 +335,8 @@ inline adjusted_mantissa positive_digit_comp(bigint& bigmant, int32_t exponent)
 // we then need to scale by `2^(f- e)`, and then the two significant digits
 // are of the same magnitude.
 template <typename T>
-inline adjusted_mantissa negative_digit_comp(bigint& bigmant, adjusted_mantissa am, int32_t exponent) noexcept {
+inline FASTFLOAT_CONSTEXPR20
+adjusted_mantissa negative_digit_comp(bigint& bigmant, adjusted_mantissa am, int32_t exponent) noexcept {
   bigint& real_digits = bigmant;
   int32_t real_exp = exponent;
 
@@ -383,7 +396,8 @@ inline adjusted_mantissa negative_digit_comp(bigint& bigmant, adjusted_mantissa
 // the actual digits. we then compare the big integer representations
 // of both, and use that to direct rounding.
 template <typename T>
-inline adjusted_mantissa digit_comp(parsed_number_string& num, adjusted_mantissa am) noexcept {
+inline FASTFLOAT_CONSTEXPR20
+adjusted_mantissa digit_comp(parsed_number_string& num, adjusted_mantissa am) noexcept {
   // remove the invalid exponent bias
   am.power2 -= invalid_am_bias;
 

include/fast_float/fast_float.h

@@ -3,6 +3,8 @@
 
 #include <system_error>
 
+#include "constexpr_feature_detect.h"
+
 namespace fast_float {
 enum chars_format {
     scientific = 1<<0,
@@ -48,6 +50,7 @@ struct parse_options {
  * The default is  `fast_float::chars_format::general` which allows both `fixed` and `scientific`.
  */
 template<typename T>
+FASTFLOAT_CONSTEXPR20
 from_chars_result from_chars(const char *first, const char *last,
                              T &value, chars_format fmt = chars_format::general)  noexcept;
 
@@ -55,6 +58,7 @@ from_chars_result from_chars(const char *first, const char *last,
  * Like from_chars, but accepts an `options` argument to govern number parsing.
  */
 template<typename T>
+FASTFLOAT_CONSTEXPR20
 from_chars_result from_chars_advanced(const char *first, const char *last,
                                       T &value, parse_options options)  noexcept;
 

include/fast_float/float_common.h

@@ -7,23 +7,8 @@
 #include <cstring>
 #include <type_traits>
 
-#ifdef __has_include
+#if FASTFLOAT_HAS_BIT_CAST
-#if __has_include(<version>)
-#include <version>
-#endif
-#endif
-
-#if __cpp_lib_bit_cast >= 201806L
 #include <bit>
-#define FASTFLOAT_HAS_BIT_CAST 1
-#else
-#define FASTFLOAT_HAS_BIT_CAST 0
-#endif
-
-#if __cpp_lib_is_constant_evaluated >= 201811L
-#define FASTFLOAT_HAS_IS_CONSTANT_EVALUATED 1
-#else
-#define FASTFLOAT_HAS_IS_CONSTANT_EVALUATED 0
 #endif
 
 #if (defined(__x86_64) || defined(__x86_64__) || defined(_M_X64)   \
@@ -110,22 +95,6 @@
 // rust style `try!()` macro, or `?` operator
 #define FASTFLOAT_TRY(x) { if (!(x)) return false; }
 
-// Testing for https://wg21.link/N3652, adopted in C++14
-#if __cpp_constexpr >= 201304
-#define FASTFLOAT_CONSTEXPR14 constexpr
-#else
-#define FASTFLOAT_CONSTEXPR14
-#endif
-
-// Testing for relevant C++20 constexpr library features
-#if FASTFLOAT_HAS_IS_CONSTANT_EVALUATED \
-    && FASTFLOAT_HAS_BIT_CAST \
-    && __cpp_lib_constexpr_algorithms >= 201806L /*For std::copy and std::fill*/
-#define FASTFLOAT_CONSTEXPR20 constexpr
-#else
-#define FASTFLOAT_CONSTEXPR20
-#endif
-
 namespace fast_float {
 
 fastfloat_really_inline constexpr bool cpp20_and_in_constexpr() {

include/fast_float/parse_number.h

@@ -20,8 +20,9 @@ namespace detail {
  * strings a null-free and fixed.
  **/
 template <typename T>
-from_chars_result parse_infnan(const char *first, const char *last, T &value)  noexcept  {
+from_chars_result FASTFLOAT_CONSTEXPR14
-  from_chars_result answer;
+parse_infnan(const char *first, const char *last, T &value)  noexcept  {
+  from_chars_result answer{};
   answer.ptr = first;
   answer.ec = std::errc(); // be optimistic
   bool minusSign = false;
@@ -132,12 +133,14 @@ fastfloat_really_inline bool rounds_to_nearest() noexcept {
 } // namespace detail
 
 template<typename T>
+FASTFLOAT_CONSTEXPR20
 from_chars_result from_chars(const char *first, const char *last,
                              T &value, chars_format fmt /*= chars_format::general*/)  noexcept  {
   return from_chars_advanced(first, last, value, parse_options{fmt});
 }
 
 template<typename T>
+FASTFLOAT_CONSTEXPR20
 from_chars_result from_chars_advanced(const char *first, const char *last,
                                       T &value, parse_options options)  noexcept  {
 
@@ -174,7 +177,7 @@ from_chars_result from_chars_advanced(const char *first, const char *last,
     // 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())  {
+    if(!cpp20_and_in_constexpr() && 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()) {
@@ -191,7 +194,7 @@ from_chars_result from_chars_advanced(const char *first, const char *last,
 #if defined(__clang__)
         // Clang may map 0 to -0.0 when fegetround() == FE_DOWNWARD
         if(pns.mantissa == 0) {
-          value = 0;
+          value = pns.negative ? -0. : 0.;
           return answer;
         }
 #endif

script/amalgamate.py

@@ -31,7 +31,7 @@ for filename in ['LICENSE-MIT', 'LICENSE-APACHE']:
   processed_files[filename] = text
 
 # code
-for filename in [ 'fast_float.h', 'float_common.h', 'ascii_number.h', 
+for filename in [ 'constexpr_feature_detect.h', 'fast_float.h', 'float_common.h', 'ascii_number.h', 
                   'fast_table.h', 'decimal_to_binary.h', 'bigint.h',
                   'ascii_number.h', 'digit_comparison.h', 'parse_number.h']:
   with open('include/fast_float/' + filename, encoding='utf8') as f:
@@ -75,6 +75,7 @@ def license_content(license_arg):
 text = ''.join([
   processed_files['AUTHORS'], processed_files['CONTRIBUTORS'], 
   *license_content(args.license),
+  processed_files['constexpr_feature_detect.h'],
   processed_files['fast_float.h'], processed_files['float_common.h'], 
   processed_files['ascii_number.h'], processed_files['fast_table.h'],
   processed_files['decimal_to_binary.h'], processed_files['bigint.h'],

tests/CMakeLists.txt

@@ -60,7 +60,13 @@ fast_float_add_cpp_test(rcppfastfloat_test)
 fast_float_add_cpp_test(example_test)
 fast_float_add_cpp_test(example_comma_test)
 fast_float_add_cpp_test(basictest)
+option(FASTFLOAT_CONSTEXPR_TESTS "Constexpr tests" OFF)
+if (FASTFLOAT_CONSTEXPR_TESTS)
+  target_compile_features(basictest PRIVATE cxx_std_20)
+  target_compile_definitions(basictest PRIVATE FASTFLOAT_CONSTEXPR_TESTS)
+else()
   target_compile_features(basictest PRIVATE cxx_std_17)
+endif()
 
 fast_float_add_cpp_test(long_test)
 fast_float_add_cpp_test(powersoffive_hardround)

tests/basictest.cpp

@@ -10,8 +10,13 @@
 #include <limits>
 #include <string>
 #include <system_error>
+#include <type_traits>
 #include <cfenv>
 
+#if FASTFLOAT_HAS_BIT_CAST
+#include <bit>
+#endif
+
 #ifndef SUPPLEMENTAL_TEST_DATA_DIR
 #define SUPPLEMENTAL_TEST_DATA_DIR "data/"
 #endif
@@ -184,6 +189,53 @@ TEST_CASE("parse_zero") {
   CHECK(float64_parsed == 0);
 }
 
+TEST_CASE("parse_negative_zero") {
+  //
+  // If this function fails, we may be left in a non-standard rounding state.
+  //
+  const char * negative_zero = "-0";
+  uint64_t float64_parsed;
+  double f = -0.;
+  ::memcpy(&float64_parsed, &f, sizeof(f));
+  CHECK(float64_parsed == 0x8000'0000'0000'0000);
+
+  fesetround(FE_UPWARD);
+  auto r1 = fast_float::from_chars(negative_zero, negative_zero + 2, f);
+  CHECK(r1.ec == std::errc());
+  std::cout << "FE_UPWARD parsed negative 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 == 0x8000'0000'0000'0000);
+
+  fesetround(FE_TOWARDZERO);
+  auto r2 = fast_float::from_chars(negative_zero, negative_zero + 2, f);
+  CHECK(r2.ec == std::errc());
+  std::cout << "FE_TOWARDZERO parsed negative 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 == 0x8000'0000'0000'0000);
+
+  fesetround(FE_DOWNWARD);
+  auto r3 = fast_float::from_chars(negative_zero, negative_zero + 2, f);
+  CHECK(r3.ec == std::errc());
+  std::cout << "FE_DOWNWARD parsed negative 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 == 0x8000'0000'0000'0000);
+
+  fesetround(FE_TONEAREST);
+  auto r4 = fast_float::from_chars(negative_zero, negative_zero + 2, f);
+  CHECK(r4.ec == std::errc());
+  std::cout << "FE_TONEAREST parsed negative 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 == 0x8000'0000'0000'0000);
+}
+
 // 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)
@@ -572,53 +624,147 @@ std::string append_zeros(std::string str, size_t number_of_zeros) {
   return answer;
 }
 
-template<class T>
+namespace {
-void check_basic_test_result(const std::string& str, fast_float::from_chars_result result,
+
+enum class Diag { runtime, comptime };
+
+} // anonymous namespace
+
+template <Diag diag, class T>
+constexpr void check_basic_test_result(std::string_view str,
+                                       fast_float::from_chars_result result,
                                        T actual, T expected) {
-  INFO("str=" << str << "\n"
+  if constexpr (diag == Diag::runtime) {
+      INFO(
+          "str=" << str << "\n"
                  << "  expected=" << fHexAndDec(expected) << "\n"
                  << "  ..actual=" << fHexAndDec(actual) << "\n"
-       << "  expected mantissa=" << iHexAndDec(get_mantissa(expected)) << "\n"
+                 << "  expected mantissa=" << iHexAndDec(get_mantissa(expected))
+                 << "\n"
                  << "  ..actual mantissa=" << iHexAndDec(get_mantissa(actual)));
-  CHECK_EQ(result.ec, std::errc());
-  CHECK_EQ(result.ptr, str.data() + str.size());
-  CHECK_EQ(copysign(1, actual), copysign(1, expected));
-  CHECK_EQ(std::isnan(actual), std::isnan(expected));
-  CHECK_EQ(actual, expected);
   }
 
-template<class T>
+  struct ComptimeDiag {
-void basic_test(std::string str, T expected) {
+      // Purposely not constexpr
+      static void error_not_equal() {}
+  };
+
+#define FASTFLOAT_CHECK_EQ(...)                                                \
+  if constexpr (diag == Diag::runtime) {                                       \
+    CHECK_EQ(__VA_ARGS__);                                                     \
+  } else {                                                                     \
+    if ([](const auto &lhs, const auto &rhs) {                                 \
+          return lhs != rhs;                                                   \
+        }(__VA_ARGS__)) {                                                      \
+      ComptimeDiag::error_not_equal();                                         \
+    }                                                                          \
+  }
+
+  auto copysign = [](double x, double y) -> double {
+#if FASTFLOAT_HAS_BIT_CAST
+    if (fast_float::cpp20_and_in_constexpr()) {
+      using equiv_int = std::make_signed_t<
+          typename fast_float::binary_format<double>::equiv_uint>;
+      const auto i = std::bit_cast<equiv_int>(y);
+      if (i < 0) {
+        return -x;
+      }
+      return x;
+    }
+#endif
+    return std::copysign(x, y);
+  };
+
+  auto isnan = [](double x) -> bool {
+    return x != x;
+  };
+
+  FASTFLOAT_CHECK_EQ(result.ec, std::errc());
+  FASTFLOAT_CHECK_EQ(result.ptr, str.data() + str.size());
+  FASTFLOAT_CHECK_EQ(copysign(1, actual), copysign(1, expected));
+  FASTFLOAT_CHECK_EQ(isnan(actual), isnan(expected));
+  FASTFLOAT_CHECK_EQ(actual, expected);
+
+#undef FASTFLOAT_CHECK_EQ
+}
+
+template<Diag diag, class T>
+constexpr void basic_test(std::string_view str, T expected) {
   T actual;
   auto result = fast_float::from_chars(str.data(), str.data() + str.size(), actual);
-  check_basic_test_result(str, result, actual, expected);
+  check_basic_test_result<diag>(str, result, actual, expected);
 }
 
-template<class T>
+template<Diag diag, class T>
-void basic_test(std::string str, T expected, fast_float::parse_options options) {
+constexpr void basic_test(std::string_view str, T expected, fast_float::parse_options options) {
   T actual;
   auto result = fast_float::from_chars_advanced(str.data(), str.data() + str.size(), actual, options);
-  check_basic_test_result(str, result, actual, expected);
+  check_basic_test_result<diag>(str, result, actual, expected);
 }
 
 void basic_test(float val) {
   {
       std::string long_vals = to_long_string(val);
       INFO("long vals: " << long_vals);
-      basic_test<float>(long_vals, val);
+      basic_test<Diag::runtime, float>(long_vals, val);
   }
   {
       std::string vals = to_string(val);
       INFO("vals: " << vals);
-      basic_test<float>(vals, val);
+      basic_test<Diag::runtime, float>(vals, val);
   }
 }
 
-#define verify(lhs, rhs) { INFO(lhs); basic_test(lhs, rhs); }
+#define verify_runtime(lhs, rhs)                                               \
+  do {                                                                         \
+    INFO(lhs);                                                                 \
+    basic_test<Diag::runtime>(lhs, rhs);                                       \
+  } while (false)
+
+#define verify_comptime(lhs, rhs)                                              \
+  do {                                                                         \
+    constexpr int verify_comptime_var =                                        \
+        (basic_test<Diag::comptime>(lhs, rhs), 0);                             \
+    (void)verify_comptime_var;                                                 \
+  } while (false)
+
+#define verify_options_runtime(lhs, rhs)                                       \
+  do {                                                                         \
+    INFO(lhs);                                                                 \
+    basic_test<Diag::runtime>(lhs, rhs, options);                              \
+  } while (false)
+
+#define verify_options_comptime(lhs, rhs)                                      \
+  do {                                                                         \
+    constexpr int verify_options_comptime_var =                                \
+        (basic_test<Diag::comptime>(lhs, rhs, options), 0);                    \
+    (void)verify_options_comptime_var;                                         \
+  } while (false)
+
+#if defined(FASTFLOAT_CONSTEXPR_TESTS)
+#if !FASTFLOAT_IS_CONSTEXPR
+#error "from_chars must be constexpr for constexpr tests"
+#endif
+
+#define verify(lhs, rhs)                                                       \
+  do {                                                                         \
+    verify_runtime(lhs, rhs);                                                  \
+    verify_comptime(lhs, rhs);                                                 \
+  } while (false)
+
+#define verify_options(lhs, rhs)                                               \
+  do {                                                                         \
+    verify_options_runtime(lhs, rhs);                                          \
+    verify_options_comptime(lhs, rhs);                                         \
+  } while (false)
+
+#else
+#define verify verify_runtime
+#define verify_options verify_options_runtime
+#endif
+
 #define verify32(val) { INFO(#val); basic_test(val); }
 
-#define verify_options(lhs, rhs) { INFO(lhs); basic_test(lhs, rhs, options); }
-
 TEST_CASE("64bit.inf") {
   verify("INF", std::numeric_limits<double>::infinity());
   verify("-INF", -std::numeric_limits<double>::infinity());
@@ -644,7 +790,7 @@ TEST_CASE("64bit.general") {
   verify("-2.2222222222223e-322",-0x1.68p-1069);
   verify("9007199254740993.0", 0x1p+53);
   verify("860228122.6654514319E+90", 0x1.92bb20990715fp+328);
-  verify(append_zeros("9007199254740993.0",1000), 0x1p+53);
+  verify_runtime(append_zeros("9007199254740993.0",1000), 0x1p+53);
   verify("10000000000000000000", 0x1.158e460913dp+63);
   verify("10000000000000000000000000000001000000000000", 0x1.cb2d6f618c879p+142);
   verify("10000000000000000000000000000000000000000001", 0x1.cb2d6f618c879p+142);
@@ -701,8 +847,11 @@ TEST_CASE("64bit.general") {
 }
 
 TEST_CASE("64bit.decimal_point") {
-  fast_float::parse_options options{};
+  constexpr auto options = []{
-  options.decimal_point = ',';
+    fast_float::parse_options ret{};
+    ret.decimal_point = ',';
+    return ret;
+  }();
 
   // infinities
   verify_options("1,8e308", std::numeric_limits<double>::infinity());
@@ -715,7 +864,7 @@ TEST_CASE("64bit.decimal_point") {
   verify_options("-2,2222222222223e-322",-0x1.68p-1069);
   verify_options("9007199254740993,0", 0x1p+53);
   verify_options("860228122,6654514319E+90", 0x1.92bb20990715fp+328);
-  verify_options(append_zeros("9007199254740993,0",1000), 0x1p+53);
+  verify_options_runtime(append_zeros("9007199254740993,0",1000), 0x1p+53);
   verify_options("1,1920928955078125e-07", 1.1920928955078125e-07);
   verify_options("9355950000000000000,00000000000000000000000000000000001844674407370955161600000184467440737095516161844674407370955161407370955161618446744073709551616000184467440737095516166000001844674407370955161618446744073709551614073709551616184467440737095516160001844674407370955161601844674407370955674451616184467440737095516140737095516161844674407370955161600018446744073709551616018446744073709551611616000184467440737095001844674407370955161600184467440737095516160018446744073709551168164467440737095516160001844073709551616018446744073709551616184467440737095516160001844674407536910751601611616000184467440737095001844674407370955161600184467440737095516160018446744073709551616184467440737095516160001844955161618446744073709551616000184467440753691075160018446744073709",0x1.03ae05e8fca1cp+63);
   verify_options("2,22507385850720212418870147920222032907240528279439037814303133837435107319244194686754406432563881851382188218502438069999947733013005649884107791928741341929297200970481951993067993290969042784064731682041565926728632933630474670123316852983422152744517260835859654566319282835244787787799894310779783833699159288594555213714181128458251145584319223079897504395086859412457230891738946169368372321191373658977977723286698840356390251044443035457396733706583981055420456693824658413747607155981176573877626747665912387199931904006317334709003012790188175203447190250028061277777916798391090578584006464715943810511489154282775041174682194133952466682503431306181587829379004205392375072083366693241580002758391118854188641513168478436313080237596295773983001708984375e-308", 0x1.0000000000002p-1022);
@@ -778,16 +927,16 @@ TEST_CASE("32bit.general") {
   verify("-1e-999",-0.0f);
   verify("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125", 0x1.2ced3p+0f);
   verify("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125e-38", 0x1.fffff8p-127f);
-  verify(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",655), 0x1.2ced3p+0f);
+  verify_runtime(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",655), 0x1.2ced3p+0f);
-  verify(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",656), 0x1.2ced3p+0f);
+  verify_runtime(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",656), 0x1.2ced3p+0f);
-  verify(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",1000), 0x1.2ced3p+0f);
+  verify_runtime(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",1000), 0x1.2ced3p+0f);
   std::string test_string;
   test_string = append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",655) + std::string("e-38");
-  verify(test_string, 0x1.fffff8p-127f);
+  verify_runtime(test_string, 0x1.fffff8p-127f);
   test_string = append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",656) + std::string("e-38");
-  verify(test_string, 0x1.fffff8p-127f);
+  verify_runtime(test_string, 0x1.fffff8p-127f);
   test_string = append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",1000) + std::string("e-38");
-  verify(test_string, 0x1.fffff8p-127f);
+  verify_runtime(test_string, 0x1.fffff8p-127f);
   verify32(1.00000006e+09f);
   verify32(1.4012984643e-45f);
   verify32(1.1754942107e-38f);
@@ -852,8 +1001,11 @@ TEST_CASE("32bit.general") {
 }
 
 TEST_CASE("32bit.decimal_point") {
-  fast_float::parse_options options{};
+  constexpr auto options = [] {
-  options.decimal_point = ',';
+    fast_float::parse_options ret{};
+    ret.decimal_point = ',';
+    return ret;
+  }();
 
   // infinity
   verify_options("3,5028234666e38", std::numeric_limits<float>::infinity());
@@ -861,16 +1013,16 @@ TEST_CASE("32bit.decimal_point") {
   // finites
   verify_options("1,1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125", 0x1.2ced3p+0f);
   verify_options("1,1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125e-38", 0x1.fffff8p-127f);
-  verify_options(append_zeros("1,1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",655), 0x1.2ced3p+0f);
+  verify_options_runtime(append_zeros("1,1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",655), 0x1.2ced3p+0f);
-  verify_options(append_zeros("1,1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",656), 0x1.2ced3p+0f);
+  verify_options_runtime(append_zeros("1,1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",656), 0x1.2ced3p+0f);
-  verify_options(append_zeros("1,1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",1000), 0x1.2ced3p+0f);
+  verify_options_runtime(append_zeros("1,1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",1000), 0x1.2ced3p+0f);
   std::string test_string;
   test_string = append_zeros("1,1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",655) + std::string("e-38");
-  verify_options(test_string, 0x1.fffff8p-127f);
+  verify_options_runtime(test_string, 0x1.fffff8p-127f);
   test_string = append_zeros("1,1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",656) + std::string("e-38");
-  verify_options(test_string, 0x1.fffff8p-127f);
+  verify_options_runtime(test_string, 0x1.fffff8p-127f);
   test_string = append_zeros("1,1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",1000) + std::string("e-38");
-  verify_options(test_string, 0x1.fffff8p-127f);
+  verify_options_runtime(test_string, 0x1.fffff8p-127f);
   verify_options("1,1754943508e-38", 1.1754943508e-38f);
   verify_options("30219,0830078125", 30219.0830078125f);
   verify_options("1,1754947011469036e-38", 0x1.000006p-126f);

tests/long_random64.cpp

@@ -62,6 +62,7 @@ void random_values(size_t N) {
         if (errors > 10) {
           abort();
         }
+        continue;
       }
       if (std::isnan(v)) {
         if (!std::isnan(result_value)) {

tests/random64.cpp

@@ -65,6 +65,7 @@ void random_values(size_t N) {
         if (errors > 10) {
           abort();
         }
+        continue;
       }
       if (std::isnan(v)) {
         if (!std::isnan(result_value)) {