1 files changed, 17 insertions, 12 deletions

diff --git a/test/fuzzing/float.cc b/test/fuzzing/float.cc
index a9a347ef..d4c9e4f5 100644
--- a/test/fuzzing/float.cc
+++ b/test/fuzzing/float.cc
@@ -1,34 +1,39 @@
 // A fuzzer for floating-point formatter.
 // For the license information refer to format.h.
 
+#include <fmt/format.h>
+
 #include <cstdint>
 #include <cstdlib>
-#include <stdexcept>
 #include <limits>
-#include <fmt/format.h>
+#include <stdexcept>
 
 #include "fuzzer-common.h"
 
-extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
-  if (size <= sizeof(double) || !std::numeric_limits<double>::is_iec559)
-    return 0;
-
-  auto value = assign_from_buf<double>(data);
+void check_round_trip(fmt::string_view format_str, double value) {
   auto buffer = fmt::memory_buffer();
-  fmt::format_to(buffer, "{}", value);
+  fmt::format_to(std::back_inserter(buffer), format_str, value);
 
-  // Check a round trip.
   if (std::isnan(value)) {
     auto nan = std::signbit(value) ? "-nan" : "nan";
     if (fmt::string_view(buffer.data(), buffer.size()) != nan)
       throw std::runtime_error("round trip failure");
-    return 0;
+    return;
   }
+
   buffer.push_back('\0');
   char* ptr = nullptr;
   if (std::strtod(buffer.data(), &ptr) != value)
     throw std::runtime_error("round trip failure");
-  if (ptr + 1 != buffer.end())
-    throw std::runtime_error("unparsed output");
+  if (ptr + 1 != buffer.end()) throw std::runtime_error("unparsed output");
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  if (size <= sizeof(double) || !std::numeric_limits<double>::is_iec559)
+    return 0;
+  check_round_trip("{}", assign_from_buf<double>(data));
+  // A larger than necessary precision is used to trigger the fallback
+  // formatter.
+  check_round_trip("{:.50g}", assign_from_buf<double>(data));
   return 0;
 }