Add json fmt test

include/fast_float/ascii_number.h

@@ -312,9 +312,11 @@ parsed_number_string_t<UC> parse_number_string(UC const *p, UC const * pend, par
   UC const * const end_of_integer_part = p;
   int64_t digit_count = int64_t(end_of_integer_part - start_digits);
   answer.integer = span<const UC>(start_digits, size_t(digit_count));
-  // disallow leading zeros
-  if (fmt == chars_format::json && start_digits[0] == UC('0') && digit_count > 1) {
-    return answer;
+  if (fmt == chars_format::json) {
+    // at least 1 digit in integer part, without leading zeros
+    if (digit_count == 0 || (start_digits[0] == UC('0') && digit_count > 1)) {
+      return answer;
+    }
   }
 
   int64_t exponent = 0;
@@ -335,12 +337,13 @@ parsed_number_string_t<UC> parse_number_string(UC const *p, UC const * pend, par
     answer.fraction = span<const UC>(before, size_t(p - before));
     digit_count -= exponent;
   }
-  // we must have encountered at least one integer!
-  if (digit_count == 0) {
-    return answer;
-  }
-  // or at least two if a decimal point exists, with json rules
-  else if (fmt == chars_format::json && has_decimal_point && digit_count == 1) {
+  if (fmt == chars_format::json) {
+    // at least 1 digit in fractional part
+    if (has_decimal_point && exponent == 0) {
+      return answer;
+    }
+  } 
+  else if (digit_count == 0) { // we must have encountered at least one integer!
     return answer;
   }
   int64_t exp_number = 0;            // explicit exponential part

tests/CMakeLists.txt

@@ -72,6 +72,8 @@ fast_float_add_cpp_test(long_test)
 fast_float_add_cpp_test(powersoffive_hardround)
 fast_float_add_cpp_test(string_test)
 
+fast_float_add_cpp_test(json_fmt)
+
 
 
 option(FASTFLOAT_EXHAUSTIVE "Exhaustive tests" OFF)

tests/json_fmt.cpp

@@ -0,0 +1,38 @@
+
+#include <cstdlib>
+#include <iostream>
+#include <vector>
+
+#include "fast_float/fast_float.h"
+
+int main()
+{
+  const std::vector<double> expected{ -0.2, 0.02, 0.002, 1., 0. };
+  const std::vector<std::string> accept{ "-0.2", "0.02", "0.002", "1e+0000", "0e-2" };
+  const std::vector<std::string> reject{ "-.2", "00.02", "0.e+1", "00.e+1", ".25"};
+  const auto fmt = fast_float::chars_format::json;
+
+  for (std::size_t i = 0; i < accept.size(); ++i)
+  {
+    const auto& f = accept[i];
+    double result;
+    auto answer = fast_float::from_chars(f.data(), f.data() + f.size(), result, fmt);
+    if (answer.ec != std::errc() || result != expected[i]) {
+      std::cerr << "json fmt rejected valid json " << f << std::endl;
+      return EXIT_FAILURE;
+    }
+  }
+
+  for (std::size_t i = 0; i < reject.size(); ++i)
+  {
+    const auto& f = reject[i];
+    double result;
+    auto answer = fast_float::from_chars(f.data(), f.data() + f.size(), result, fmt);
+    if (answer.ec == std::errc()) {
+      std::cerr << "json fmt accepted invalid json " << f << std::endl;
+      return EXIT_FAILURE;
+    }
+  }
+
+  return EXIT_SUCCESS;
+}