[boa-dev#524] add implementation for Math.fround()

boa/src/builtins/math/mod.rs

@@ -255,6 +255,21 @@ impl Math {
             .into())
     }
 
+    /// Get the nearest 32-bit single precision float representation of a number.
+    ///
+    /// More information:
+    ///  - [ECMAScript reference][spec]
+    ///  - [MDN documentation][mdn]
+    ///
+    /// [spec]: https://tc39.es/ecma262/#sec-math.fround
+    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/fround
+    pub(crate) fn fround(_: &Value, args: &[Value], _: &mut Interpreter) -> ResultValue {
+        Ok(args
+            .get(0)
+            .map_or(f64::NAN, |x| (f64::from(x) as f32) as f64)
+            .into())
+    }
+
     /// Get the natural logarithm of a number.
     ///
     /// More information:
@@ -530,6 +545,7 @@ impl Math {
         make_builtin_fn(Self::exp, "exp", &math, 1);
         make_builtin_fn(Self::expm1, "expm1", &math, 1);
         make_builtin_fn(Self::floor, "floor", &math, 1);
+        make_builtin_fn(Self::fround, "fround", &math, 1);
         make_builtin_fn(Self::log, "log", &math, 1);
         make_builtin_fn(Self::log10, "log10", &math, 1);
         make_builtin_fn(Self::log2, "log2", &math, 1);

boa/src/builtins/math/tests.rs

@@ -330,6 +330,36 @@ fn floor() {
     assert_eq!(c.to_number(), 3_f64);
 }
 
+#[test]
+fn fround() {
+    let realm = Realm::create();
+    let mut engine = Interpreter::new(realm);
+    let init = r#"
+        var a = Math.fround(NaN);
+        var b = Math.fround(Infinity);
+        var c = Math.fround(5);
+        var d = Math.fround(5.5);
+        var e = Math.fround(5.05);
+        var f = Math.fround(-5.05);
+        "#;
+
+    eprintln!("{}", forward(&mut engine, init));
+
+    let a = forward(&mut engine, "a");
+    let b = forward(&mut engine, "b");
+    let c = forward_val(&mut engine, "c").unwrap();
+    let d = forward_val(&mut engine, "d").unwrap();
+    let e = forward_val(&mut engine, "e").unwrap();
+    let f = forward_val(&mut engine, "f").unwrap();
+
+    assert_eq!(a, String::from("NaN"));
+    assert_eq!(b, String::from("Infinity"));
+    assert_eq!(c.to_number(), 5f64);
+    assert_eq!(d.to_number(), 5.5f64);
+    assert_eq!(e.to_number(), 5.050_000_190_734_863);
+    assert_eq!(f.to_number(), -5.050_000_190_734_863);
+}
+
 #[test]
 fn log() {
     let realm = Realm::create();