Replace use_grisu with fallback since Grisu is only one of multiple implemented algorithms

include/fmt/core.h

@@ -2676,7 +2676,7 @@ struct float_specs {
   bool upper : 1;
   bool locale : 1;
   bool binary32 : 1;
-  bool use_grisu : 1;
+  bool fallback : 1;
   bool showpoint : 1;
 };
 

include/fmt/format-inl.h

@@ -2375,7 +2375,7 @@ FMT_HEADER_ONLY_CONSTEXPR20 int format_float(Float value, int precision,
     return -precision;
   }
 
-  if (!specs.use_grisu) return snprintf_float(value, precision, specs, buf);
+  if (specs.fallback) return snprintf_float(value, precision, specs, buf);
 
   if (!is_constant_evaluated() && precision < 0) {
     // Use Dragonbox for the shortest format.

include/fmt/format.h

@@ -1995,7 +1995,7 @@ FMT_CONSTEXPR20 auto write(OutputIt out, T value,
       ++precision;
   }
   if (const_check(std::is_same<T, float>())) fspecs.binary32 = true;
-  fspecs.use_grisu = is_fast_float<T>();
+  if (!is_fast_float<T>()) fspecs.fallback = true;
   int exp = format_float(promote_float(value), precision, fspecs, buffer);
   fspecs.precision = precision;
   auto fp = big_decimal_fp{buffer.data(), static_cast<int>(buffer.size()), exp};