Add roundeven and roundevenf

Author: Jules-Bertholet

libm/build.rs

@@ -39,6 +39,9 @@ mod musl_reference_tests {
         "jnf.rs",
         "j1.rs",
         "j1f.rs",
+        // musl doens't have these
+        "roundeven.rs",
+        "roundevenf.rs",
     ];
 
     struct Function {

libm/src/math/mod.rs

@@ -171,6 +171,8 @@ mod remainderf;
 mod remquo;
 mod remquof;
 mod round;
+mod roundeven;
+mod roundevenf;
 mod roundf;
 mod scalbn;
 mod scalbnf;
@@ -285,6 +287,8 @@ pub use self::remainderf::remainderf;
 pub use self::remquo::remquo;
 pub use self::remquof::remquof;
 pub use self::round::round;
+pub use self::roundeven::roundeven;
+pub use self::roundevenf::roundevenf;
 pub use self::roundf::roundf;
 pub use self::scalbn::scalbn;
 pub use self::scalbnf::scalbnf;

libm/src/math/roundeven.rs

@@ -0,0 +1,50 @@
+// Source: musl libm rint
+// (equivalent to roundeven when rounding mode is default,
+// which Rust assumes)
+
+#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
+pub fn roundeven(x: f64) -> f64 {
+    let one_over_e = 1.0 / f64::EPSILON;
+    let as_u64: u64 = x.to_bits();
+    let exponent: u64 = as_u64 >> 52 & 0x7ff;
+    let is_positive = (as_u64 >> 63) == 0;
+    if exponent >= 0x3ff + 52 {
+        x
+    } else {
+        let ans = if is_positive {
+            x + one_over_e - one_over_e
+        } else {
+            x - one_over_e + one_over_e
+        };
+
+        if ans == 0.0 {
+            if is_positive {
+                0.0
+            } else {
+                -0.0
+            }
+        } else {
+            ans
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::roundeven;
+
+    #[test]
+    fn negative_zero() {
+        assert_eq!(roundeven(-0.0_f64).to_bits(), (-0.0_f64).to_bits());
+    }
+
+    #[test]
+    fn sanity_check() {
+        assert_eq!(roundeven(-1.0), -1.0);
+        assert_eq!(roundeven(2.8), 3.0);
+        assert_eq!(roundeven(-0.5), -0.0);
+        assert_eq!(roundeven(0.5), 0.0);
+        assert_eq!(roundeven(-1.5), -2.0);
+        assert_eq!(roundeven(1.5), 2.0);
+    }
+}

libm/src/math/roundevenf.rs

@@ -0,0 +1,50 @@
+// Source: musl libm rintf
+// (equivalent to roundevenf when rounding mode is default,
+// which Rust assumes)
+
+#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
+pub fn roundevenf(x: f32) -> f32 {
+    let one_over_e = 1.0 / f32::EPSILON;
+    let as_u32: u32 = x.to_bits();
+    let exponent: u32 = as_u32 >> 23 & 0xff;
+    let is_positive = (as_u32 >> 31) == 0;
+    if exponent >= 0x7f + 23 {
+        x
+    } else {
+        let ans = if is_positive {
+            x + one_over_e - one_over_e
+        } else {
+            x - one_over_e + one_over_e
+        };
+
+        if ans == 0.0 {
+            if is_positive {
+                0.0
+            } else {
+                -0.0
+            }
+        } else {
+            ans
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::roundevenf;
+
+    #[test]
+    fn negative_zero() {
+        assert_eq!(roundevenf(-0.0_f32).to_bits(), (-0.0_f32).to_bits());
+    }
+
+    #[test]
+    fn sanity_check() {
+        assert_eq!(roundevenf(-1.0), -1.0);
+        assert_eq!(roundevenf(2.8), 3.0);
+        assert_eq!(roundevenf(-0.5), -0.0);
+        assert_eq!(roundevenf(0.5), 0.0);
+        assert_eq!(roundevenf(-1.5), -2.0);
+        assert_eq!(roundevenf(1.5), 2.0);
+    }
+}