more clear NAN names and fix broken_floats logic

Co-authored-by: Jubilee <46493976+workingjubilee@users.noreply.github.com>

Author: RalfJung

tests/ui/consts/const-float-bits-conv.rs

@@ -46,14 +46,15 @@ fn f32() {
 
     // Check that NaNs roundtrip their bits regardless of signalingness
     // 0xA is 0b1010; 0x5 is 0b0101 -- so these two together clobbers all the mantissa bits
-    const MASKED_NAN1: u32 = f32::NAN.to_bits() ^ 0x002A_AAAA;
-    const MASKED_NAN2: u32 = f32::NAN.to_bits() ^ 0x0055_5555;
+    // NOTE: These names assume `f{BITS}::NAN` is a quiet NAN and IEEE754-2008's NaN rules apply!
+    const QUIET_NAN: u32 = f32::NAN.to_bits() ^ 0x002A_AAAA;
+    const SIGNALING_NAN: u32 = f32::NAN.to_bits() ^ 0x0055_5555;
 
-    const_assert!(f32::from_bits(MASKED_NAN1).is_nan());
-    const_assert!(f32::from_bits(MASKED_NAN2).is_nan());
-    const_assert!(f32::from_bits(MASKED_NAN1).to_bits(), MASKED_NAN1);
+    const_assert!(f32::from_bits(QUIET_NAN).is_nan());
+    const_assert!(f32::from_bits(SIGNALING_NAN).is_nan());
+    const_assert!(f32::from_bits(QUIET_NAN).to_bits(), QUIET_NAN);
     if !has_broken_floats() {
-        const_assert!(f32::from_bits(MASKED_NAN2).to_bits(), MASKED_NAN2);
+        const_assert!(f32::from_bits(SIGNALING_NAN).to_bits(), SIGNALING_NAN);
     }
 }
 
@@ -75,14 +76,15 @@ fn f64() {
 
     // Check that NaNs roundtrip their bits regardless of signalingness
     // 0xA is 0b1010; 0x5 is 0b0101 -- so these two together clobbers all the mantissa bits
-    const MASKED_NAN1: u64 = f64::NAN.to_bits() ^ 0x000A_AAAA_AAAA_AAAA;
-    const MASKED_NAN2: u64 = f64::NAN.to_bits() ^ 0x0005_5555_5555_5555;
+    // NOTE: These names assume `f{BITS}::NAN` is a quiet NAN and IEEE754-2008's NaN rules apply!
+    const QUIET_NAN: u64 = f64::NAN.to_bits() ^ 0x0005_5555_5555_5555;
+    const SIGNALING_NAN: u64 = f64::NAN.to_bits() ^ 0x000A_AAAA_AAAA_AAAA;
 
-    const_assert!(f64::from_bits(MASKED_NAN1).is_nan());
-    const_assert!(f64::from_bits(MASKED_NAN2).is_nan());
-    const_assert!(f64::from_bits(MASKED_NAN1).to_bits(), MASKED_NAN1);
+    const_assert!(f64::from_bits(QUIET_NAN).is_nan());
+    const_assert!(f64::from_bits(SIGNALING_NAN).is_nan());
+    const_assert!(f64::from_bits(QUIET_NAN).to_bits(), QUIET_NAN);
     if !has_broken_floats() {
-        const_assert!(f64::from_bits(MASKED_NAN2).to_bits(), MASKED_NAN2);
+        const_assert!(f64::from_bits(SIGNALING_NAN).to_bits(), SIGNALING_NAN);
     }
 }