Use correct exponential representation for rational values (#493)

Co-authored-by: HalidOdat <halidodat@gmail.com>

Cargo.lock

@@ -16,6 +16,7 @@ dependencies = [
  "rand",
  "regex",
  "rustc-hash",
+ "ryu-js",
  "serde",
  "serde_json",
 ]
@@ -806,6 +807,11 @@ version = "1.0.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "71d301d4193d031abdd79ff7e3dd721168a9572ef3fe51a1517aba235bd8f86e"
 
+[[package]]
+name = "ryu-js"
+version = "1.0.5"
+source = "git+https://github.com/Tropid/ryu-js#fe366fa397d04324fa693b5d85134851b09719b3"
+
 [[package]]
 name = "same-file"
 version = "1.0.6"

boa/Cargo.toml

@@ -23,6 +23,7 @@ rustc-hash = "1.1.0"
 num-bigint = { version = "0.3.0", features = ["serde"] }
 num-integer = "0.1.43"
 bitflags = "1.2.1"
+ryu-js = "0.2.0"
 
 # Optional Dependencies
 serde = { version = "1.0.114", features = ["derive"], optional = true }

boa/src/builtins/value/display.rs

@@ -177,19 +177,15 @@ impl Display for Value {
                 None => write!(f, "Symbol()"),
             },
             Self::String(ref v) => write!(f, "{}", v),
-            Self::Rational(v) => write!(
-                f,
-                "{}",
-                match v {
-                    _ if v.is_nan() => "NaN".to_string(),
-                    _ if v.is_infinite() && v.is_sign_negative() => "-Infinity".to_string(),
-                    _ if v.is_infinite() => "Infinity".to_string(),
-                    _ => v.to_string(),
-                }
-            ),
+            Self::Rational(v) => format_rational(*v, f),
             Self::Object(_) => write!(f, "{}", log_string_from(self, true)),
             Self::Integer(v) => write!(f, "{}", v),
             Self::BigInt(ref num) => write!(f, "{}n", num),
         }
     }
 }
+
+fn format_rational(v: f64, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    let mut buffer = ryu_js::Buffer::new();
+    write!(f, "{}", buffer.format(v))
+}

boa/src/builtins/value/tests.rs

@@ -214,6 +214,40 @@ fn get_types() {
     );
 }
 
+#[test]
+fn to_string() {
+    let f64_to_str = |f| Value::Rational(f).to_string();
+
+    assert_eq!(f64_to_str(f64::NAN), "NaN");
+    assert_eq!(f64_to_str(0.0), "0");
+    assert_eq!(f64_to_str(f64::INFINITY), "Infinity");
+    assert_eq!(f64_to_str(f64::NEG_INFINITY), "-Infinity");
+    assert_eq!(f64_to_str(90.12), "90.12");
+    assert_eq!(f64_to_str(111111111111111111111.0), "111111111111111110000");
+    assert_eq!(
+        f64_to_str(1111111111111111111111.0),
+        "1.1111111111111111e+21"
+    );
+
+    assert_eq!(f64_to_str(-90.12), "-90.12");
+
+    assert_eq!(
+        f64_to_str(-111111111111111111111.0),
+        "-111111111111111110000"
+    );
+    assert_eq!(
+        f64_to_str(-1111111111111111111111.0),
+        "-1.1111111111111111e+21"
+    );
+
+    assert_eq!(f64_to_str(0.0000001), "1e-7");
+    assert_eq!(f64_to_str(0.000001), "0.000001");
+    assert_eq!(f64_to_str(0.0000002), "2e-7");
+    assert_eq!(f64_to_str(-0.0000001), "-1e-7");
+
+    assert_eq!(f64_to_str(3e50), "3e+50");
+}
+
 #[test]
 fn add_number_and_number() {
     let realm = Realm::create();