diff --git a/library/compiler-builtins/libm/crates/libm-test/Cargo.toml b/library/compiler-builtins/libm/crates/libm-test/Cargo.toml
index b6e2ced5877d..760340e518c7 100644
--- a/library/compiler-builtins/libm/crates/libm-test/Cargo.toml
+++ b/library/compiler-builtins/libm/crates/libm-test/Cargo.toml
@@ -15,6 +15,12 @@ test-musl-serialized = ["rand"]
 anyhow = "1.0.90"
 libm = { path = "../.." }
 libm-macros = { path = "../libm-macros" }
+rand = "0.8.5"
+rand_chacha = "0.3.1"
+
+[target.'cfg(target_family = "wasm")'.dependencies]
+# Enable randomness on WASM
+getrandom = { version = "0.2", features = ["js"] }
 
 [build-dependencies]
 rand = { version = "0.8.5", optional = true }
diff --git a/library/compiler-builtins/libm/crates/libm-test/src/gen.rs b/library/compiler-builtins/libm/crates/libm-test/src/gen.rs
index 12e17d476538..3e9eca37a677 100644
--- a/library/compiler-builtins/libm/crates/libm-test/src/gen.rs
+++ b/library/compiler-builtins/libm/crates/libm-test/src/gen.rs
@@ -1,6 +1,7 @@
 //! Different generators that can create random or systematic bit patterns.
 
 use crate::GenerateInput;
+pub mod random;
 
 /// Helper type to turn any reusable input into a generator.
 #[derive(Clone, Debug, Default)]
diff --git a/library/compiler-builtins/libm/crates/libm-test/src/gen/random.rs b/library/compiler-builtins/libm/crates/libm-test/src/gen/random.rs
new file mode 100644
index 000000000000..e5964319569d
--- /dev/null
+++ b/library/compiler-builtins/libm/crates/libm-test/src/gen/random.rs
@@ -0,0 +1,125 @@
+//! A simple generator that produces deterministic random input, caching to use the same
+//! inputs for all functions.
+
+use std::sync::LazyLock;
+
+use rand::{Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
+
+use super::CachedInput;
+use crate::GenerateInput;
+
+const SEED: [u8; 32] = *b"3.141592653589793238462643383279";
+
+/// Number of tests to run.
+const NTESTS: usize = {
+    let ntests = if cfg!(optimizations_enabled) {
+        if cfg!(target_arch = "x86_64") || cfg!(target_arch = "aarch64") {
+            5_000_000
+        } else if !cfg!(target_pointer_width = "64")
+            || cfg!(all(target_arch = "x86_64", target_vendor = "apple"))
+            || option_env!("EMULATED").is_some()
+                && cfg!(any(target_arch = "aarch64", target_arch = "powerpc64"))
+        {
+            // Tests are pretty slow on:
+            // - Non-64-bit targets
+            // - Emulated ppc
+            // - Emulated aarch64
+            // - x86 MacOS
+            // So reduce the number of iterations
+            100_000
+        } else {
+            // Most everything else gets tested in docker and works okay, but we still
+            // don't need 20 minutes of tests.
+            1_000_000
+        }
+    } else {
+        800
+    };
+
+    ntests
+};
+
+/// Tested inputs.
+static TEST_CASES: LazyLock<CachedInput> = LazyLock::new(|| make_test_cases(NTESTS));
+
+/// The first argument to `jn` and `jnf` is the number of iterations. Make this a reasonable
+/// value so tests don't run forever.
+static TEST_CASES_JN: LazyLock<CachedInput> = LazyLock::new(|| {
+    // Start with regular test cases
+    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));
+
+    // It is easy to overflow the stack with these in debug mode
+    let max_iterations = if cfg!(optimizations_enabled) && cfg!(target_pointer_width = "64") {
+        0xffff
+    } else if cfg!(windows) {
+        0x00ff
+    } else {
+        0x0fff
+    };
+
+    let mut rng = ChaCha8Rng::from_seed(SEED);
+
+    for case in cases.inputs_i32.iter_mut() {
+        case.0 = rng.gen_range(3..=max_iterations);
+    }
+
+    cases
+});
+
+fn make_test_cases(ntests: usize) -> CachedInput {
+    let mut rng = ChaCha8Rng::from_seed(SEED);
+
+    // make sure we include some basic cases
+    let mut inputs_i32 = vec![(0, 0, 0), (1, 1, 1), (-1, -1, -1)];
+    let mut inputs_f32 = vec![
+        (0.0, 0.0, 0.0),
+        (f32::EPSILON, f32::EPSILON, f32::EPSILON),
+        (f32::INFINITY, f32::INFINITY, f32::INFINITY),
+        (f32::NEG_INFINITY, f32::NEG_INFINITY, f32::NEG_INFINITY),
+        (f32::MAX, f32::MAX, f32::MAX),
+        (f32::MIN, f32::MIN, f32::MIN),
+        (f32::MIN_POSITIVE, f32::MIN_POSITIVE, f32::MIN_POSITIVE),
+        (f32::NAN, f32::NAN, f32::NAN),
+    ];
+    let mut inputs_f64 = vec![
+        (0.0, 0.0, 0.0),
+        (f64::EPSILON, f64::EPSILON, f64::EPSILON),
+        (f64::INFINITY, f64::INFINITY, f64::INFINITY),
+        (f64::NEG_INFINITY, f64::NEG_INFINITY, f64::NEG_INFINITY),
+        (f64::MAX, f64::MAX, f64::MAX),
+        (f64::MIN, f64::MIN, f64::MIN),
+        (f64::MIN_POSITIVE, f64::MIN_POSITIVE, f64::MIN_POSITIVE),
+        (f64::NAN, f64::NAN, f64::NAN),
+    ];
+
+    inputs_i32.extend((0..(ntests - inputs_i32.len())).map(|_| rng.gen::<(i32, i32, i32)>()));
+
+    // Generate integers to get a full range of bitpatterns, then convert back to
+    // floats.
+    inputs_f32.extend((0..(ntests - inputs_f32.len())).map(|_| {
+        let ints = rng.gen::<(u32, u32, u32)>();
+        (f32::from_bits(ints.0), f32::from_bits(ints.1), f32::from_bits(ints.2))
+    }));
+    inputs_f64.extend((0..(ntests - inputs_f64.len())).map(|_| {
+        let ints = rng.gen::<(u64, u64, u64)>();
+        (f64::from_bits(ints.0), f64::from_bits(ints.1), f64::from_bits(ints.2))
+    }));
+
+    CachedInput { inputs_f32, inputs_f64, inputs_i32 }
+}
+
+/// Create a test case iterator.
+pub fn get_test_cases<RustArgs>(fname: &str) -> 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)
+}