More fixed precision tests

include/fmt/format-inl.h

@@ -588,7 +588,7 @@ struct fixed_handler {
   }
 
   digits::result on_digit(char digit, uint64_t divisor, uint64_t remainder,
-                          uint64_t error, int& exp, bool integral) {
+                          uint64_t error, int, bool integral) {
     FMT_ASSERT(remainder < divisor, "");
     buf[size++] = digit;
     if (size != precision) return digits::more;
@@ -601,7 +601,6 @@ struct fixed_handler {
       FMT_ASSERT(error == 1 && divisor > 2, "");
     }
     auto dir = get_round_direction(divisor, remainder, error);
-    // TODO: test rounding
     if (dir != up) return dir == down ? digits::done : digits::error;
     ++buf[size - 1];
     for (int i = size - 1; i > 0 && buf[i] > '9'; --i) {
@@ -610,7 +609,7 @@ struct fixed_handler {
     }
     if (buf[0] > '9') {
       buf[0] = '1';
-      ++exp;
+      buf[size++] = '0';
     }
     return digits::done;
   }

test/format-test.cc

@@ -1476,7 +1476,13 @@ TEST(FormatterTest, PrecisionRounding) {
   EXPECT_EQ("0.001", format("{:.3f}", 0.0005));
   EXPECT_EQ("0.001", format("{:.3f}", 0.00149));
   EXPECT_EQ("0.002", format("{:.3f}", 0.0015));
+  EXPECT_EQ("1.000", format("{:.3f}", 0.9999));
   EXPECT_EQ("0.00123", format("{:.3}", 0.00123));
+  // Trigger rounding error in Grisu by a carefully chosen number.
+  auto n = 3788512123356.985352;
+  char buffer[64];
+  sprintf(buffer, "%f", n);
+  EXPECT_EQ(buffer, format("{:f}", n));
 }
 
 TEST(FormatterTest, FormatNaN) {