add FMA test that would fail with apfloat

Author: RalfJung

src/shims/intrinsics/mod.rs

@@ -324,7 +324,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
             "fmaf32" => {
                 let [a, b, c] = check_arg_count(args)?;
-                // FIXME: Using host floats, to work around https://github.com/rust-lang/miri/issues/2468.
+                // FIXME: Using host floats, to work around https://github.com/rust-lang/rustc_apfloat/issues/11
                 let a = f32::from_bits(this.read_scalar(a)?.to_u32()?);
                 let b = f32::from_bits(this.read_scalar(b)?.to_u32()?);
                 let c = f32::from_bits(this.read_scalar(c)?.to_u32()?);
@@ -334,7 +334,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
             "fmaf64" => {
                 let [a, b, c] = check_arg_count(args)?;
-                // FIXME: Using host floats, to work around https://github.com/rust-lang/miri/issues/2468.
+                // FIXME: Using host floats, to work around https://github.com/rust-lang/rustc_apfloat/issues/11
                 let a = f64::from_bits(this.read_scalar(a)?.to_u64()?);
                 let b = f64::from_bits(this.read_scalar(b)?.to_u64()?);
                 let c = f64::from_bits(this.read_scalar(c)?.to_u64()?);

tests/pass/intrinsics-math.rs

@@ -1,4 +1,5 @@
 #![feature(float_gamma)]
+use std::{f32, f64};
 
 macro_rules! assert_approx_eq {
     ($a:expr, $b:expr) => {{
@@ -15,8 +16,7 @@ fn ldexp(a: f64, b: i32) -> f64 {
 }
 
 pub fn main() {
-    use std::f32;
-    use std::f64;
+    mul_add();
 
     assert_approx_eq!(64f32.sqrt(), 8f32);
     assert_approx_eq!(64f64.sqrt(), 8f64);
@@ -48,13 +48,6 @@ pub fn main() {
     assert_approx_eq!(8f32.log2(), 3f32);
     assert_approx_eq!(f64::consts::E.log2(), f64::consts::LOG2_E);
 
-    assert_approx_eq!(3.0f32.mul_add(2.0f32, 5.0f32), 11.0);
-    assert_eq!(0.0f32.mul_add(-2.0, f32::consts::E), f32::consts::E);
-    assert_approx_eq!(3.0f64.mul_add(2.0, 5.0), 11.0);
-    assert_eq!(0.0f64.mul_add(-2.0f64, f64::consts::E), f64::consts::E);
-    assert_eq!((-3.2f32).mul_add(2.4, f32::NEG_INFINITY), f32::NEG_INFINITY);
-    assert_eq!((-3.2f64).mul_add(2.4, f64::NEG_INFINITY), f64::NEG_INFINITY);
-
     assert_approx_eq!((-1.0f32).abs(), 1.0f32);
     assert_approx_eq!(34.2f64.abs(), 34.2f64);
 
@@ -146,3 +139,19 @@ pub fn main() {
     assert_approx_eq!(val, (2.0 * f64::consts::PI.sqrt()).ln());
     assert_eq!(sign, -1);
 }
+
+fn mul_add() {
+    assert_approx_eq!(3.0f32.mul_add(2.0f32, 5.0f32), 11.0);
+    assert_eq!(0.0f32.mul_add(-2.0, f32::consts::E), f32::consts::E);
+    assert_approx_eq!(3.0f64.mul_add(2.0, 5.0), 11.0);
+    assert_eq!(0.0f64.mul_add(-2.0f64, f64::consts::E), f64::consts::E);
+    assert_eq!((-3.2f32).mul_add(2.4, f32::NEG_INFINITY), f32::NEG_INFINITY);
+    assert_eq!((-3.2f64).mul_add(2.4, f64::NEG_INFINITY), f64::NEG_INFINITY);
+
+    let f = f32::mul_add(
+        -0.000000000000000000000000000000000000014728589,
+        0.0000037105144,
+        0.000000000000000000000000000000000000000000055,
+    );
+    assert_eq!(f.to_bits(), f32::to_bits(-0.0));
+}