exp10: Add cr_exp10 from CORE-MATH

libm-test/src/f8_impl.rs

@@ -90,6 +90,10 @@ impl Float for f8 {
         libm::generic::copysign(self, other)
     }
 
+    fn roundeven(self) -> Self {
+        libm::generic::rint_status(self).val
+    }
+
     fn fma(self, _y: Self, _z: Self) -> Self {
         unimplemented!()
     }

libm-test/src/precision.rs

@@ -93,7 +93,8 @@ pub fn default_ulp(ctx: &CheckCtx) -> Option<u32> {
         Bn::Erf => 1,
         Bn::Erfc => 4,
         Bn::Exp => 1,
-        Bn::Exp10 => 6,
+        Bn::Exp10 if ctx.fn_ident == Id::Exp10f => 6,
+        Bn::Exp10 => 0,
         Bn::Exp2 => 1,
         Bn::Expm1 => 1,
         Bn::Hypot => 1,

libm/src/math/approx/exp10f64.rs

@@ -0,0 +1,23 @@
+use super::super::{exp2, modf, pow};
+
+const LN10: f64 = 3.32192809488736234787031942948939;
+const P10: &[f64] = &[
+    1e-15, 1e-14, 1e-13, 1e-12, 1e-11, 1e-10, 1e-9, 1e-8, 1e-7, 1e-6, 1e-5, 1e-4, 1e-3, 1e-2, 1e-1,
+    1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10, 1e11, 1e12, 1e13, 1e14, 1e15,
+];
+
+/// Calculates 10 raised to the power of `x` (f64).
+#[cfg_attr(assert_no_panic, no_panic::no_panic)]
+pub fn exp10f64(x: f64) -> f64 {
+    let (mut y, n) = modf(x);
+    let u: u64 = n.to_bits();
+    /* fabs(n) < 16 without raising invalid on nan */
+    if ((u >> 52) & 0x7ff) < 0x3ff + 4 {
+        if y == 0.0 {
+            return i!(P10, ((n as isize) + 15) as usize);
+        }
+        y = exp2(LN10 * y);
+        return y * i!(P10, ((n as isize) + 15) as usize);
+    }
+    return pow(10.0, x);
+}

libm/src/math/approx/mod.rs

@@ -4,5 +4,7 @@
 //! not be as accurate.
 
 mod cbrtf64;
+mod exp10f64;
 
 pub use cbrtf64::cbrtf64;
+pub use exp10f64::exp10f64;