implement the rounding intrinsics using apfloat rounding

Author: RalfJung

src/tools/miri/src/shims/intrinsics/mod.rs

@@ -145,17 +145,30 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             "fabsf32" => {
                 let [f] = check_arg_count(args)?;
                 let f = this.read_scalar(f)?.to_f32()?;
-                // Can be implemented in soft-floats.
                 // This is a "bitwise" operation, so there's no NaN non-determinism.
                 this.write_scalar(Scalar::from_f32(f.abs()), dest)?;
             }
             "fabsf64" => {
                 let [f] = check_arg_count(args)?;
                 let f = this.read_scalar(f)?.to_f64()?;
-                // Can be implemented in soft-floats.
                 // This is a "bitwise" operation, so there's no NaN non-determinism.
                 this.write_scalar(Scalar::from_f64(f.abs()), dest)?;
             }
+            "floorf32" | "ceilf32" | "truncf32" | "roundf32" | "rintf32" => {
+                let [f] = check_arg_count(args)?;
+                let f = this.read_scalar(f)?.to_f32()?;
+                let mode = match intrinsic_name {
+                    "floorf32" => Round::TowardNegative,
+                    "ceilf32" => Round::TowardPositive,
+                    "truncf32" => Round::TowardZero,
+                    "roundf32" => Round::NearestTiesToAway,
+                    "rintf32" => Round::NearestTiesToEven,
+                    _ => bug!(),
+                };
+                let res = f.round_to_integral(mode).value;
+                let res = this.adjust_nan(res, &[f]);
+                this.write_scalar(res, dest)?;
+            }
             #[rustfmt::skip]
             | "sinf32"
             | "cosf32"
@@ -165,11 +178,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             | "logf32"
             | "log10f32"
             | "log2f32"
-            | "floorf32"
-            | "ceilf32"
-            | "truncf32"
-            | "roundf32"
-            | "rintf32"
             => {
                 let [f] = check_arg_count(args)?;
                 let f = this.read_scalar(f)?.to_f32()?;
@@ -184,18 +192,28 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                     "logf32" => f_host.ln(),
                     "log10f32" => f_host.log10(),
                     "log2f32" => f_host.log2(),
-                    "floorf32" => f_host.floor(),
-                    "ceilf32" => f_host.ceil(),
-                    "truncf32" => f_host.trunc(),
-                    "roundf32" => f_host.round(),
-                    "rintf32" => f_host.round_ties_even(),
                     _ => bug!(),
                 };
                 let res = res.to_soft();
                 let res = this.adjust_nan(res, &[f]);
                 this.write_scalar(res, dest)?;
             }
 
+            "floorf64" | "ceilf64" | "truncf64" | "roundf64" | "rintf64" => {
+                let [f] = check_arg_count(args)?;
+                let f = this.read_scalar(f)?.to_f64()?;
+                let mode = match intrinsic_name {
+                    "floorf64" => Round::TowardNegative,
+                    "ceilf64" => Round::TowardPositive,
+                    "truncf64" => Round::TowardZero,
+                    "roundf64" => Round::NearestTiesToAway,
+                    "rintf64" => Round::NearestTiesToEven,
+                    _ => bug!(),
+                };
+                let res = f.round_to_integral(mode).value;
+                let res = this.adjust_nan(res, &[f]);
+                this.write_scalar(res, dest)?;
+            }
             #[rustfmt::skip]
             | "sinf64"
             | "cosf64"
@@ -205,11 +223,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             | "logf64"
             | "log10f64"
             | "log2f64"
-            | "floorf64"
-            | "ceilf64"
-            | "truncf64"
-            | "roundf64"
-            | "rintf64"
             => {
                 let [f] = check_arg_count(args)?;
                 let f = this.read_scalar(f)?.to_f64()?;
@@ -224,11 +237,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                     "logf64" => f_host.ln(),
                     "log10f64" => f_host.log10(),
                     "log2f64" => f_host.log2(),
-                    "floorf64" => f_host.floor(),
-                    "ceilf64" => f_host.ceil(),
-                    "truncf64" => f_host.trunc(),
-                    "roundf64" => f_host.round(),
-                    "rintf64" => f_host.round_ties_even(),
                     _ => bug!(),
                 };
                 let res = res.to_soft();

src/tools/miri/tests/pass/float_nan.rs

@@ -264,6 +264,10 @@ fn test_f32() {
         HashSet::from_iter([F32::nan(Pos, Quiet, 0), F32::nan(Neg, Quiet, 0)]),
         || F32::from(f32::min(nan, nan)),
     );
+    check_all_outcomes(
+        HashSet::from_iter([F32::nan(Pos, Quiet, 0), F32::nan(Neg, Quiet, 0)]),
+        || F32::from(nan.floor()),
+    );
     check_all_outcomes(
         HashSet::from_iter([F32::nan(Pos, Quiet, 0), F32::nan(Neg, Quiet, 0)]),
         || F32::from(nan.sin()),
@@ -376,6 +380,10 @@ fn test_f64() {
         HashSet::from_iter([F64::nan(Pos, Quiet, 0), F64::nan(Neg, Quiet, 0)]),
         || F64::from(f64::min(nan, nan)),
     );
+    check_all_outcomes(
+        HashSet::from_iter([F64::nan(Pos, Quiet, 0), F64::nan(Neg, Quiet, 0)]),
+        || F64::from(nan.floor()),
+    );
     check_all_outcomes(
         HashSet::from_iter([F64::nan(Pos, Quiet, 0), F64::nan(Neg, Quiet, 0)]),
         || F64::from(nan.sin()),

src/tools/miri/tests/pass/intrinsics-math.rs

@@ -1,4 +1,5 @@
 #![feature(float_gamma)]
+#![feature(round_ties_even)]
 use std::{f32, f64};
 
 macro_rules! assert_approx_eq {
@@ -73,7 +74,14 @@ pub fn main() {
     assert_approx_eq!(3.0f64.hypot(4.0f64), 5.0f64);
 
     assert_eq!(3.3_f32.round(), 3.0);
-    assert_eq!(3.3_f64.round(), 3.0);
+    assert_eq!(2.5_f32.round(), 3.0);
+    assert_eq!(3.9_f64.round(), 4.0);
+    assert_eq!(2.5_f64.round(), 3.0);
+
+    assert_eq!(3.3_f32.round_ties_even(), 3.0);
+    assert_eq!(2.5_f32.round_ties_even(), 2.0);
+    assert_eq!(3.9_f64.round_ties_even(), 4.0);
+    assert_eq!(2.5_f64.round_ties_even(), 2.0);
 
     assert_eq!(ldexp(0.65f64, 3i32), 5.2f64);
     assert_eq!(ldexp(1.42, 0xFFFF), f64::INFINITY);