1 files changed, 37 insertions, 0 deletions
diff --git a/library/compiler-builtins/libm/src/math/nextafter.rs b/library/compiler-builtins/libm/src/math/nextafter.rs
new file mode 100644
index 00000000000..c991ff6f233
--- /dev/null
+++ b/library/compiler-builtins/libm/src/math/nextafter.rs
@@ -0,0 +1,37 @@
+#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
+pub fn nextafter(x: f64, y: f64) -> f64 {
+    if x.is_nan() || y.is_nan() {
+        return x + y;
+    }
+
+    let mut ux_i = x.to_bits();
+    let uy_i = y.to_bits();
+    if ux_i == uy_i {
+        return y;
+    }
+
+    let ax = ux_i & (!1_u64 / 2);
+    let ay = uy_i & (!1_u64 / 2);
+    if ax == 0 {
+        if ay == 0 {
+            return y;
+        }
+        ux_i = (uy_i & (1_u64 << 63)) | 1;
+    } else if ax > ay || ((ux_i ^ uy_i) & (1_u64 << 63)) != 0 {
+        ux_i -= 1;
+    } else {
+        ux_i += 1;
+    }
+
+    let e = (ux_i >> 52) & 0x7ff;
+    // raise overflow if ux.f is infinite and x is finite
+    if e == 0x7ff {
+        force_eval!(x + x);
+    }
+    let ux_f = f64::from_bits(ux_i);
+    // raise underflow if ux.f is subnormal or zero
+    if e == 0 {
+        force_eval!(x * x + ux_f * ux_f);
+    }
+    ux_f
+}