Fix negating f16 and f128 constants

compiler/rustc_mir_build/src/build/mod.rs

@@ -1023,7 +1023,13 @@ pub(crate) fn parse_float_into_scalar(
     let num = num.as_str();
     match float_ty {
         // FIXME(f16_f128): When available, compare to the library parser as with `f32` and `f64`
-        ty::FloatTy::F16 => num.parse::<Half>().ok().map(Scalar::from_f16),
+        ty::FloatTy::F16 => {
+            let mut f = num.parse::<Half>().ok()?;
+            if neg {
+                f = -f;
+            }
+            Some(Scalar::from_f16(f))
+        }
         ty::FloatTy::F32 => {
             let Ok(rust_f) = num.parse::<f32>() else { return None };
             let mut f = num
@@ -1071,7 +1077,13 @@ pub(crate) fn parse_float_into_scalar(
             Some(Scalar::from_f64(f))
         }
         // FIXME(f16_f128): When available, compare to the library parser as with `f32` and `f64`
-        ty::FloatTy::F128 => num.parse::<Quad>().ok().map(Scalar::from_f128),
+        ty::FloatTy::F128 => {
+            let mut f = num.parse::<Quad>().ok()?;
+            if neg {
+                f = -f;
+            }
+            Some(Scalar::from_f128(f))
+        }
     }
 }
 

tests/ui/numbers-arithmetic/f16-f128-lit.rs

@@ -0,0 +1,16 @@
+//@ run-pass
+
+#![feature(f16)]
+#![feature(f128)]
+
+fn main() {
+    assert_eq!(0.0_f16.to_bits(), 0x0000);
+    assert_eq!((-0.0_f16).to_bits(), 0x8000);
+    assert_eq!(10.0_f16.to_bits(), 0x4900);
+    assert_eq!((-10.0_f16).to_bits(), 0xC900);
+
+    assert_eq!(0.0_f128.to_bits(), 0x0000_0000_0000_0000_0000_0000_0000_0000);
+    assert_eq!((-0.0_f128).to_bits(), 0x8000_0000_0000_0000_0000_0000_0000_0000);
+    assert_eq!(10.0_f128.to_bits(), 0x4002_4000_0000_0000_0000_0000_0000_0000);
+    assert_eq!((-10.0_f128).to_bits(), 0xC002_4000_0000_0000_0000_0000_0000_0000);
+}