Merge pull request #272 from Jules-Bertholet/roundeven

Author: Amanieu

libm/crates/libm-bench/benches/bench.rs

@@ -107,7 +107,8 @@ macro_rules! bessel {
 
 unary!(
     acos, acosh, asin, atan, cbrt, ceil, cos, cosh, erf, exp, exp2, exp10, expm1, fabs, floor, j0,
-    j1, lgamma, log, log1p, log2, log10, round, sin, sinh, sqrt, tan, tanh, tgamma, trunc, y0, y1
+    j1, lgamma, log, log1p, log2, log10, rint, round, sin, sinh, sqrt, tan, tanh, tgamma, trunc,
+    y0, y1
 );
 binary!(atan2, copysign, fdim, fmax, fmin, fmod, hypot, pow);
 trinary!(fma);

libm/src/math/mod.rs

@@ -170,6 +170,8 @@ mod remainder;
 mod remainderf;
 mod remquo;
 mod remquof;
+mod rint;
+mod rintf;
 mod round;
 mod roundf;
 mod scalbn;
@@ -284,6 +286,8 @@ pub use self::remainder::remainder;
 pub use self::remainderf::remainderf;
 pub use self::remquo::remquo;
 pub use self::remquof::remquof;
+pub use self::rint::rint;
+pub use self::rintf::rintf;
 pub use self::round::round;
 pub use self::roundf::roundf;
 pub use self::scalbn::scalbn;

libm/src/math/rint.rs

@@ -0,0 +1,48 @@
+#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
+pub fn rint(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
+        }
+    }
+}
+
+// PowerPC tests are failing on LLVM 13: https://github.com/rust-lang/rust/issues/88520
+#[cfg(not(target_arch = "powerpc64"))]
+#[cfg(test)]
+mod tests {
+    use super::rint;
+
+    #[test]
+    fn negative_zero() {
+        assert_eq!(rint(-0.0_f64).to_bits(), (-0.0_f64).to_bits());
+    }
+
+    #[test]
+    fn sanity_check() {
+        assert_eq!(rint(-1.0), -1.0);
+        assert_eq!(rint(2.8), 3.0);
+        assert_eq!(rint(-0.5), -0.0);
+        assert_eq!(rint(0.5), 0.0);
+        assert_eq!(rint(-1.5), -2.0);
+        assert_eq!(rint(1.5), 2.0);
+    }
+}

libm/src/math/rintf.rs

@@ -0,0 +1,48 @@
+#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
+pub fn rintf(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
+        }
+    }
+}
+
+// PowerPC tests are failing on LLVM 13: https://github.com/rust-lang/rust/issues/88520
+#[cfg(not(target_arch = "powerpc64"))]
+#[cfg(test)]
+mod tests {
+    use super::rintf;
+
+    #[test]
+    fn negative_zero() {
+        assert_eq!(rintf(-0.0_f32).to_bits(), (-0.0_f32).to_bits());
+    }
+
+    #[test]
+    fn sanity_check() {
+        assert_eq!(rintf(-1.0), -1.0);
+        assert_eq!(rintf(2.8), 3.0);
+        assert_eq!(rintf(-0.5), -0.0);
+        assert_eq!(rintf(0.5), 0.0);
+        assert_eq!(rintf(-1.5), -2.0);
+        assert_eq!(rintf(1.5), 2.0);
+    }
+}