Fix libm based f{32,64}.{floor,ceil,trunc} corner cases (#1860)

* update libm

* use libm::roundeven in f{32,64}_nearest impl

* make it possible to test libm implementation

This adds the libm crate feature to the following crates:
- wasmi_core
- wasmi
- wasmi_wast

* opt into_quiet_nan by using unlikely in branch

* fix libm based ceil, floor and trunc impls

Author: Robbepop

crates/core/Cargo.toml

@@ -14,7 +14,7 @@ categories.workspace = true
 exclude.workspace = true
 
 [dependencies]
-libm = { version = "0.2.11", default-features = false }
+libm = { version = "0.2.16", default-features = false }
 
 [features]
 default = ["std"]
@@ -25,6 +25,7 @@ std = []
 # This also changes the size of `RawVal` from 64-bit to 128-bit
 # which may have significant impact on performance and memory usage.
 simd = []
+libm = []
 
 [package.metadata.cargo-udeps.ignore]
 # cargo-udeps cannot detect that libm is used for no_std targets only.

crates/core/src/value.rs

@@ -444,7 +444,7 @@ trait WasmFloatExt {
     fn mul_add(self, a: Self, b: Self) -> Self;
 }
 
-#[cfg(not(feature = "std"))]
+#[cfg(any(not(feature = "std"), feature = "libm"))]
 macro_rules! impl_wasm_float {
     ($ty:ty) => {
         impl WasmFloatExt for $ty {
@@ -455,33 +455,34 @@ macro_rules! impl_wasm_float {
 
             #[inline]
             fn ceil(self) -> Self {
+                if let Some(qnan) = self.into_quiet_nan() {
+                    return qnan;
+                }
                 <libm::Libm<Self>>::ceil(self)
             }
 
             #[inline]
             fn floor(self) -> Self {
+                if let Some(qnan) = self.into_quiet_nan() {
+                    return qnan;
+                }
                 <libm::Libm<Self>>::floor(self)
             }
 
             #[inline]
             fn trunc(self) -> Self {
+                if let Some(qnan) = self.into_quiet_nan() {
+                    return qnan;
+                }
                 <libm::Libm<Self>>::trunc(self)
             }
 
             #[inline]
             fn nearest(self) -> Self {
-                let round = <libm::Libm<Self>>::round(self);
-                if <Self as WasmFloatExt>::abs(self - <Self as WasmFloatExt>::trunc(self)) != 0.5 {
-                    return round;
-                }
-                let rem = round % 2.0;
-                if rem == 1.0 {
-                    <Self as WasmFloatExt>::floor(self)
-                } else if rem == -1.0 {
-                    <Self as WasmFloatExt>::ceil(self)
-                } else {
-                    round
+                if let Some(qnan) = self.into_quiet_nan() {
+                    return qnan;
                 }
+                <libm::Libm<Self>>::roundeven(self)
             }
 
             #[inline]
@@ -522,21 +523,19 @@ impl V128 {
 }
 
 /// Extension trait for `f32` and `f64` to turn a NaN value into a quiet-NaN value.
-#[cfg(feature = "std")]
 trait IntoQuietNan: Sized {
     /// Converts `self` into a quiet-NaN if `self` is a NaN, otherwise returns `None`.
     fn into_quiet_nan(self) -> Option<Self>;
 }
 
-#[cfg(feature = "std")]
 macro_rules! impl_into_quiet_nan {
     ( $( ($float:ty, $bits:ty, $mask:literal) );* $(;)? ) => {
         $(
             impl IntoQuietNan for $float {
                 #[inline]
                 fn into_quiet_nan(self) -> Option<Self> {
                     const QUIET_BIT: $bits = $mask;
-                    if !self.is_nan() {
+                    if unlikely(!self.is_nan()) {
                         return None;
                     }
                     Some(Self::from_bits(self.to_bits() | QUIET_BIT))
@@ -545,13 +544,12 @@ macro_rules! impl_into_quiet_nan {
         )*
     };
 }
-#[cfg(feature = "std")]
 impl_into_quiet_nan! {
     (f32, u32, 0x0040_0000);
     (f64, u64, 0x0008_0000_0000_0000);
 }
 
-#[cfg(feature = "std")]
+#[cfg(not(any(not(feature = "std"), feature = "libm")))]
 macro_rules! impl_wasm_float {
     ($ty:ty) => {
         impl WasmFloatExt for $ty {

crates/wasmi/Cargo.toml

@@ -73,6 +73,9 @@ indirect-dispatch = []
 # - Enable if your focus is on safety.
 # - Disable if your focus is on execution speed.
 extra-checks = []
+# Forces usage of `libm` for implementations of certain Wasm operators.
+# This mostly is used for testing the `libm` based Wasmi implementation.
+libm = ["wasmi_core/libm"]
 
 [[bench]]
 name = "benches"

crates/wast/Cargo.toml

@@ -25,3 +25,4 @@ indirect-dispatch = ["wasmi/indirect-dispatch"]
 extra-checks = ["wasmi/extra-checks"]
 stable = []
 unstable = ["wasmi/unstable"]
+libm = ["wasmi/libm"]