test_nan: ensure the NAN contant is quiet

Author: RalfJung

library/std/tests/floats/f128.rs

@@ -112,6 +112,8 @@ fn test_nan() {
     assert!(!nan.is_sign_negative());
     assert!(!nan.is_normal());
     assert_eq!(Fp::Nan, nan.classify());
+    // Ensure the quiet bit is set.
+    assert!(nan.to_bits() & (1 << (f128::MANTISSA_DIGITS - 2)) != 0);
 }
 
 #[test]

library/std/tests/floats/f16.rs

@@ -95,6 +95,8 @@ fn test_nan() {
     assert!(!nan.is_sign_negative());
     assert!(!nan.is_normal());
     assert_eq!(Fp::Nan, nan.classify());
+    // Ensure the quiet bit is set.
+    assert!(nan.to_bits() & (1 << (f16::MANTISSA_DIGITS - 2)) != 0);
 }
 
 #[test]

library/std/tests/floats/f32.rs

@@ -72,6 +72,8 @@ fn test_nan() {
     assert!(nan.is_sign_positive());
     assert!(!nan.is_sign_negative());
     assert_eq!(Fp::Nan, nan.classify());
+    // Ensure the quiet bit is set.
+    assert!(nan.to_bits() & (1 << (f32::MANTISSA_DIGITS - 2)) != 0);
 }
 
 #[test]

library/std/tests/floats/f64.rs

@@ -60,6 +60,8 @@ fn test_nan() {
     assert!(nan.is_sign_positive());
     assert!(!nan.is_sign_negative());
     assert_eq!(Fp::Nan, nan.classify());
+    // Ensure the quiet bit is set.
+    assert!(nan.to_bits() & (1 << (f64::MANTISSA_DIGITS - 2)) != 0);
 }
 
 #[test]