Test against MPFR

ci/docker/aarch64-unknown-linux-gnu/Dockerfile

@@ -3,7 +3,7 @@ FROM ubuntu:24.04
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
     gcc libc6-dev ca-certificates \
-    gcc-aarch64-linux-gnu libc6-dev-arm64-cross \
+    gcc-aarch64-linux-gnu m4 make libc6-dev-arm64-cross \
     qemu-user-static
 
 ENV TOOLCHAIN_PREFIX=aarch64-linux-gnu-

ci/docker/i686-unknown-linux-gnu/Dockerfile

@@ -2,4 +2,4 @@ FROM ubuntu:24.04
 
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
-    gcc-multilib libc6-dev ca-certificates
+    gcc-multilib m4 make libc6-dev ca-certificates

ci/docker/x86_64-unknown-linux-gnu/Dockerfile

@@ -2,4 +2,4 @@ FROM ubuntu:24.04
 
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
-    gcc libc6-dev ca-certificates
+    gcc m4 make libc6-dev ca-certificates

ci/run.sh

@@ -35,6 +35,22 @@ case "$target" in
     *) extra_flags="$extra_flags --features libm-test/build-musl" ;;
 esac
 
+# Configure which targets test against MPFR
+case "$target" in
+    # MSVC cannot link MPFR
+    *windows-msvc*) ;;
+    # FIXME: MinGW should be able to build MPFR, but setup in CI is nontrivial.
+    *windows-gnu*) ;;
+    # Targets that aren't cross compiled work fine
+    # FIXME(ci): we should be able to enable aarch64 Linux here once GHA
+    # support rolls out.
+    x86_64*) extra_flags="$extra_flags --features libm-test/test-multiprecision" ;;
+    # i686 works fine, i586 does not
+    i686*) extra_flags="$extra_flags --features libm-test/test-multiprecision" ;;
+    # Apple aarch64 is native
+    aarch64*apple*) extra_flags="$extra_flags --features libm-test/test-multiprecision" ;;
+esac
+
 # FIXME: `STATUS_DLL_NOT_FOUND` testing macros on CI.
 # <https://github.com/rust-lang/rust/issues/128944>
 case "$target" in

crates/libm-test/Cargo.toml

@@ -10,18 +10,21 @@ default = []
 # Generate tests which are random inputs and the outputs are calculated with
 # musl libc.
 test-musl-serialized = ["rand"]
+test-multiprecision = ["dep:az", "dep:rug"]
 
 # Build our own musl for testing and benchmarks
 build-musl = ["dep:musl-math-sys"]
 
 [dependencies]
 anyhow = "1.0.90"
+az = { version = "1.2.1", optional = true }
 libm = { path = "../.." }
 libm-macros = { path = "../libm-macros" }
 musl-math-sys = { path = "../musl-math-sys", optional = true }
 paste = "1.0.15"
 rand = "0.8.5"
 rand_chacha = "0.3.1"
+rug = { version = "1.26.1", optional = true, default-features = false, features = ["float", "std"] }
 
 [target.'cfg(target_family = "wasm")'.dependencies]
 # Enable randomness on WASM

crates/libm-test/src/gen/random.rs

@@ -7,7 +7,7 @@ use rand::{Rng, SeedableRng};
 use rand_chacha::ChaCha8Rng;
 
 use super::CachedInput;
-use crate::GenerateInput;
+use crate::{CheckCtx, GenerateInput};
 
 const SEED: [u8; 32] = *b"3.141592653589793238462643383279";
 
@@ -40,9 +40,10 @@ static TEST_CASES_JN: LazyLock<CachedInput> = LazyLock::new(|| {
     let mut cases = (&*TEST_CASES).clone();
 
     // These functions are extremely slow, limit them
-    cases.inputs_i32.truncate((NTESTS / 1000).max(80));
-    cases.inputs_f32.truncate((NTESTS / 1000).max(80));
-    cases.inputs_f64.truncate((NTESTS / 1000).max(80));
+    let ntests_jn = (NTESTS / 1000).max(80);
+    cases.inputs_i32.truncate(ntests_jn);
+    cases.inputs_f32.truncate(ntests_jn);
+    cases.inputs_f64.truncate(ntests_jn);
 
     // It is easy to overflow the stack with these in debug mode
     let max_iterations = if cfg!(optimizations_enabled) && cfg!(target_pointer_width = "64") {
@@ -105,11 +106,10 @@ fn make_test_cases(ntests: usize) -> CachedInput {
 }
 
 /// Create a test case iterator.
-pub fn get_test_cases<RustArgs>(fname: &str) -> impl Iterator<Item = RustArgs>
+pub fn get_test_cases<RustArgs>(ctx: &CheckCtx) -> impl Iterator<Item = RustArgs>
 where
     CachedInput: GenerateInput<RustArgs>,
 {
-    let inputs = if fname == "jn" || fname == "jnf" { &TEST_CASES_JN } else { &TEST_CASES };
-
-    CachedInput::get_cases(inputs)
+    let inputs = if ctx.fname == "jn" || ctx.fname == "jnf" { &TEST_CASES_JN } else { &TEST_CASES };
+    inputs.get_cases()
 }

crates/libm-test/src/lib.rs

@@ -1,4 +1,6 @@
 pub mod gen;
+#[cfg(feature = "test-multiprecision")]
+pub mod mpfloat;
 mod num_traits;
 mod special_case;
 mod test_traits;
@@ -14,14 +16,18 @@ 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"));
 
-/// ULP allowed to differ from musl (note that musl itself may not be accurate).
+/// Default ULP allowed to differ from musl (note that musl itself may not be accurate).
 const MUSL_DEFAULT_ULP: u32 = 2;
 
-/// Certain functions have different allowed ULP (consider these xfail).
+/// Default ULP allowed to differ from multiprecision (i.e. infinite) results.
+const MULTIPREC_DEFAULT_ULP: u32 = 1;
+
+/// ULP allowed to differ from muls results.
 ///
 /// Note that these results were obtained using 400,000,000 rounds of random inputs, which
 /// is not a value used by default.
 pub fn musl_allowed_ulp(name: &str) -> u32 {
+    // Consider overrides xfail
     match name {
         #[cfg(x86_no_sse)]
         "asinh" | "asinhf" => 6,
@@ -42,6 +48,27 @@ pub fn musl_allowed_ulp(name: &str) -> u32 {
     }
 }
 
+/// ULP allowed to differ from multiprecision results.
+pub fn multiprec_allowed_ulp(name: &str) -> u32 {
+    // Consider overrides xfail
+    match name {
+        "asinh" | "asinhf" => 2,
+        "acoshf" => 4,
+        "atanh" | "atanhf" => 2,
+        "exp10" | "exp10f" => 3,
+        "j0" | "j0f" | "j1" | "j1f" => {
+            // Results seem very target-dependent
+            if cfg!(target_arch = "x86_64") { 4000 } else { 800_000 }
+        }
+        "jn" | "jnf" => 1000,
+        "lgamma" | "lgammaf" | "lgamma_r" | "lgammaf_r" => 16,
+        "sinh" | "sinhf" => 2,
+        "tanh" | "tanhf" => 2,
+        "tgamma" => 20,
+        _ => MULTIPREC_DEFAULT_ULP,
+    }
+}
+
 /// Return the unsuffixed version of a function name; e.g. `abs` and `absf` both return `abs`,
 /// `lgamma_r` and `lgammaf_r` both return `lgamma_r`.
 pub fn canonical_name(name: &str) -> &str {