Optimize shortest float formatting

fmtlib · Aug 2, 2024 · d25e403 · d25e403
1 parent 1db2274
commit d25e403
Showing 1 changed file with 6 additions and 10 deletions.
diff --git a/include/fmt/format.h b/include/fmt/format.h
@@ -3194,16 +3194,6 @@ FMT_CONSTEXPR20 auto format_float(Float value, int precision,
     exp = static_cast<int>(e);
     if (e > exp) ++exp;  // Compute ceil.
     dragon_flags = dragon::fixup;
-  } else if (precision < 0) {
-    // Use Dragonbox for the shortest format.
-    if (binary32) {
-      auto dec = dragonbox::to_decimal(static_cast<float>(value));
-      write<char>(appender(buf), dec.significand);
-      return dec.exponent;
-    }
-    auto dec = dragonbox::to_decimal(static_cast<double>(value));
-    write<char>(appender(buf), dec.significand);
-    return dec.exponent;
   } else {
     // Extract significand bits and exponent bits.
     using info = dragonbox::float_info<double>;
@@ -3512,6 +3502,12 @@ FMT_CONSTEXPR20 auto write_float(OutputIt out, T value, format_specs specs,
     precision = 1;
   }
 
+  if (is_fast_float<T>::value && precision < 0) {
+    // Use Dragonbox for the shortest format.
+    using floaty = conditional_t<sizeof(T) >= sizeof(double), double, float>;
+    auto dec = dragonbox::to_decimal(static_cast<floaty>(value));
+    return write_float<Char>(out, dec, specs, sign, loc);
+  }
   int exp = format_float(convert_float(value), precision, specs,
                          std::is_same<T, float>(), buffer);