Add traits for testing

These traits give us a more generic way to interface with tuples used
for (1) test input, (2) function arguments, and (3) test input.

library/compiler-builtins/libm/crates/libm-test/src/lib.rs

@@ -1,6 +1,12 @@
 mod num_traits;
+mod test_traits;
 
 pub use num_traits::{Float, Hex, Int};
+pub use test_traits::{CheckBasis, CheckCtx, CheckOutput, GenerateInput, TupleCall};
+
+/// Result type for tests is usually from `anyhow`. Most times there is no success value to
+/// propagate.
+pub type TestResult<T = (), E = anyhow::Error> = Result<T, E>;
 
 // List of all files present in libm's source
 include!(concat!(env!("OUT_DIR"), "/all_files.rs"));

library/compiler-builtins/libm/crates/libm-test/src/num_traits.rs

@@ -1,5 +1,7 @@
 use std::fmt;
 
+use crate::TestResult;
+
 /// Common types and methods for floating point numbers.
 pub trait Float: Copy + fmt::Display + fmt::Debug + PartialEq<Self> {
     type Int: Int<OtherSign = Self::SignedInt, Unsigned = Self::Int>;
@@ -134,6 +136,29 @@ macro_rules! impl_int {
                 format!("{self:#0width$x}", width = ((Self::BITS / 4) + 2) as usize)
             }
         }
+
+        impl<Input: Hex + fmt::Debug> $crate::CheckOutput<Input> for $ty {
+            fn validate<'a>(
+                self,
+                expected: Self,
+                input: Input,
+                _ctx: &$crate::CheckCtx,
+            ) -> TestResult {
+                anyhow::ensure!(
+                    self == expected,
+                    "\
+                    \n    input:    {input:?} {ibits}\
+                    \n    expected: {expected:<22?} {expbits}\
+                    \n    actual:   {self:<22?} {actbits}\
+                    ",
+                    actbits = self.hex(),
+                    expbits = expected.hex(),
+                    ibits = input.hex(),
+                );
+
+                Ok(())
+            }
+        }
     }
 }
 

library/compiler-builtins/libm/crates/libm-test/src/test_traits.rs

@@ -0,0 +1,217 @@
+//! Traits related to testing.
+//!
+//! There are three main traits in this module:
+//!
+//! - `GenerateInput`: implemented on any types that create test cases.
+//! - `TupleCall`: implemented on tuples to allow calling them as function arguments.
+//! - `CheckOutput`: implemented on anything that is an output type for validation against an
+//!   expected value.
+
+use std::fmt;
+
+use anyhow::{Context, bail, ensure};
+
+use crate::{Float, Hex, Int, TestResult};
+
+/// Implement this on types that can generate a sequence of tuples for test input.
+pub trait GenerateInput<TupleArgs> {
+    fn get_cases(&self) -> impl Iterator<Item = TupleArgs>;
+}
+
+/// Trait for calling a function with a tuple as arguments.
+///
+/// Implemented on the tuple with the function signature as the generic (so we can use the same
+/// tuple for multiple signatures).
+pub trait TupleCall<Func>: fmt::Debug {
+    type Output;
+    fn call(self, f: Func) -> Self::Output;
+}
+
+/// Context passed to [`CheckOutput`].
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct CheckCtx {
+    /// Allowed ULP deviation
+    pub ulp: u32,
+    /// Function name.
+    pub fname: &'static str,
+    /// Source of truth for tests.
+    pub basis: CheckBasis,
+}
+
+/// Possible items to test against
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum CheckBasis {}
+
+/// A trait to implement on any output type so we can verify it in a generic way.
+pub trait CheckOutput<Input>: Sized {
+    /// Validate `self` (actual) and `expected` are the same.
+    ///
+    /// `input` is only used here for error messages.
+    fn validate<'a>(self, expected: Self, input: Input, ctx: &CheckCtx) -> TestResult;
+}
+
+impl<T1, R> TupleCall<fn(T1) -> R> for (T1,)
+where
+    T1: fmt::Debug,
+{
+    type Output = R;
+
+    fn call(self, f: fn(T1) -> R) -> Self::Output {
+        f(self.0)
+    }
+}
+
+impl<T1, T2, R> TupleCall<fn(T1, T2) -> R> for (T1, T2)
+where
+    T1: fmt::Debug,
+    T2: fmt::Debug,
+{
+    type Output = R;
+
+    fn call(self, f: fn(T1, T2) -> R) -> Self::Output {
+        f(self.0, self.1)
+    }
+}
+
+impl<T1, T2, R> TupleCall<fn(T1, &mut T2) -> R> for (T1,)
+where
+    T1: fmt::Debug,
+    T2: fmt::Debug + Default,
+{
+    type Output = (R, T2);
+
+    fn call(self, f: fn(T1, &mut T2) -> R) -> Self::Output {
+        let mut t2 = T2::default();
+        (f(self.0, &mut t2), t2)
+    }
+}
+
+impl<T1, T2, T3, R> TupleCall<fn(T1, T2, T3) -> R> for (T1, T2, T3)
+where
+    T1: fmt::Debug,
+    T2: fmt::Debug,
+    T3: fmt::Debug,
+{
+    type Output = R;
+
+    fn call(self, f: fn(T1, T2, T3) -> R) -> Self::Output {
+        f(self.0, self.1, self.2)
+    }
+}
+
+impl<T1, T2, T3, R> TupleCall<fn(T1, T2, &mut T3) -> R> for (T1, T2)
+where
+    T1: fmt::Debug,
+    T2: fmt::Debug,
+    T3: fmt::Debug + Default,
+{
+    type Output = (R, T3);
+
+    fn call(self, f: fn(T1, T2, &mut T3) -> R) -> Self::Output {
+        let mut t3 = T3::default();
+        (f(self.0, self.1, &mut t3), t3)
+    }
+}
+
+impl<T1, T2, T3> TupleCall<fn(T1, &mut T2, &mut T3)> for (T1,)
+where
+    T1: fmt::Debug,
+    T2: fmt::Debug + Default,
+    T3: fmt::Debug + Default,
+{
+    type Output = (T2, T3);
+
+    fn call(self, f: fn(T1, &mut T2, &mut T3)) -> Self::Output {
+        let mut t2 = T2::default();
+        let mut t3 = T3::default();
+        f(self.0, &mut t2, &mut t3);
+        (t2, t3)
+    }
+}
+
+// Implement for floats
+impl<F, Input> CheckOutput<Input> for F
+where
+    F: Float + Hex,
+    Input: Hex + fmt::Debug,
+    u32: TryFrom<F::SignedInt, Error: fmt::Debug>,
+{
+    fn validate<'a>(self, expected: Self, input: Input, ctx: &CheckCtx) -> TestResult {
+        // Create a wrapper function so we only need to `.with_context` once.
+        let inner = || -> TestResult {
+            // Check when both are NaNs
+            if self.is_nan() && expected.is_nan() {
+                ensure!(self.to_bits() == expected.to_bits(), "NaNs have different bitpatterns");
+                // Nothing else to check
+                return Ok(());
+            } else if self.is_nan() || expected.is_nan() {
+                // Check when only one is a NaN
+                bail!("real value != NaN")
+            }
+
+            // Make sure that the signs are the same before checing ULP to avoid wraparound
+            let act_sig = self.signum();
+            let exp_sig = expected.signum();
+            ensure!(act_sig == exp_sig, "mismatched signs {act_sig} {exp_sig}");
+
+            if self.is_infinite() ^ expected.is_infinite() {
+                bail!("mismatched infinities");
+            }
+
+            let act_bits = self.to_bits().signed();
+            let exp_bits = expected.to_bits().signed();
+
+            let ulp_diff = act_bits.checked_sub(exp_bits).unwrap().abs();
+
+            let ulp_u32 = u32::try_from(ulp_diff)
+                .map_err(|e| anyhow::anyhow!("{e:?}: ulp of {ulp_diff} exceeds u32::MAX"))?;
+
+            let allowed_ulp = ctx.ulp;
+            ensure!(ulp_u32 <= allowed_ulp, "ulp {ulp_diff} > {allowed_ulp}",);
+
+            Ok(())
+        };
+
+        inner().with_context(|| {
+            format!(
+                "\
+                \n    input:    {input:?} {ibits}\
+                \n    expected: {expected:<22?} {expbits}\
+                \n    actual:   {self:<22?} {actbits}\
+                ",
+                actbits = self.hex(),
+                expbits = expected.hex(),
+                ibits = input.hex(),
+            )
+        })
+    }
+}
+
+/// Implement `CheckOutput` for combinations of types.
+macro_rules! impl_tuples {
+    ($(($a:ty, $b:ty);)*) => {
+        $(
+            impl<Input: Hex + fmt::Debug> CheckOutput<Input> for ($a, $b) {
+                fn validate<'a>(
+                    self,
+                    expected: Self,
+                    input: Input,
+                    ctx: &CheckCtx,
+                ) -> TestResult {
+                    self.0.validate(expected.0, input, ctx,)
+                        .and_then(|()| self.1.validate(expected.1, input, ctx))
+                        .with_context(|| format!(
+                            "full input {input:?} full actual {self:?} expected {expected:?}"
+                        ))
+                }
+            }
+        )*
+    };
+}
+
+impl_tuples!(
+    (f32, i32);
+    (f64, i32);
+    (f32, f32);
+    (f64, f64);
+);