Add a generic version of rint

Use this to implement `rint` and `rintf`.

Author: tgross35

etc/function-definitions.json

@@ -654,6 +654,7 @@
             "src/libm_helper.rs",
             "src/math/arch/aarch64.rs",
             "src/math/arch/wasm32.rs",
+            "src/math/generic/rint.rs",
             "src/math/rint.rs"
         ],
         "type": "f64"
@@ -662,6 +663,7 @@
         "sources": [
             "src/math/arch/aarch64.rs",
             "src/math/arch/wasm32.rs",
+            "src/math/generic/rint.rs",
             "src/math/rintf.rs"
         ],
         "type": "f32"

src/math/generic/mod.rs

@@ -3,6 +3,7 @@ mod copysign;
 mod fabs;
 mod fdim;
 mod floor;
+mod rint;
 mod sqrt;
 mod trunc;
 
@@ -11,5 +12,6 @@ pub use copysign::copysign;
 pub use fabs::fabs;
 pub use fdim::fdim;
 pub use floor::floor;
+pub use rint::rint;
 pub use sqrt::sqrt;
 pub use trunc::trunc;

src/math/generic/rint.rs

@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: MIT */
+/* origin: musl src/math/rint.c */
+
+use super::super::Float;
+
+pub fn rint<F: Float>(x: F) -> F {
+    let toint = F::ONE / F::EPSILON;
+    let e = x.exp();
+    let positive = x.is_sign_positive();
+
+    // On i386 `force_eval!` must be used to force rounding via storage to memory. Otherwise,
+    // the excess precission from x87 would cause an incorrect final result.
+    let use_force = cfg!(x86_no_sse) && F::BITS == 32 || F::BITS == 64;
+
+    if e >= F::EXP_BIAS + F::SIG_BITS {
+        // No fractional part; exact result can be returned.
+        x
+    } else {
+        // Apply a net-zero adjustment that nudges `y` in the direction of the rounding mode.
+        let y = if positive {
+            let tmp = if use_force { force_eval!(x) } else { x } + toint;
+            (if use_force { force_eval!(tmp) } else { tmp } - toint)
+        } else {
+            let tmp = if use_force { force_eval!(x) } else { x } - toint;
+            (if use_force { force_eval!(tmp) } else { tmp } + toint)
+        };
+
+        if y == F::ZERO {
+            // A zero result takes the sign of the input.
+            if positive { F::ZERO } else { F::NEG_ZERO }
+        } else {
+            y
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn zeroes_f32() {
+        assert_biteq!(rint(0.0_f32), 0.0_f32);
+        assert_biteq!(rint(-0.0_f32), -0.0_f32);
+    }
+
+    #[test]
+    fn sanity_check_f32() {
+        assert_biteq!(rint(-1.0_f32), -1.0);
+        assert_biteq!(rint(2.8_f32), 3.0);
+        assert_biteq!(rint(-0.5_f32), -0.0);
+        assert_biteq!(rint(0.5_f32), 0.0);
+        assert_biteq!(rint(-1.5_f32), -2.0);
+        assert_biteq!(rint(1.5_f32), 2.0);
+    }
+
+    #[test]
+    fn zeroes_f64() {
+        assert_biteq!(rint(0.0_f64), 0.0_f64);
+        assert_biteq!(rint(-0.0_f64), -0.0_f64);
+    }
+
+    #[test]
+    fn sanity_check_f64() {
+        assert_biteq!(rint(-1.0_f64), -1.0);
+        assert_biteq!(rint(2.8_f64), 3.0);
+        assert_biteq!(rint(-0.5_f64), -0.0);
+        assert_biteq!(rint(0.5_f64), 0.0);
+        assert_biteq!(rint(-1.5_f64), -2.0);
+        assert_biteq!(rint(1.5_f64), 2.0);
+    }
+}

src/math/rint.rs

@@ -9,51 +9,5 @@ pub fn rint(x: f64) -> f64 {
         args: x,
     }
 
-    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 {
-            #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
-            let x = force_eval!(x);
-            let xplusoneovere = x + one_over_e;
-            #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
-            let xplusoneovere = force_eval!(xplusoneovere);
-            xplusoneovere - one_over_e
-        } else {
-            #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
-            let x = force_eval!(x);
-            let xminusoneovere = x - one_over_e;
-            #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
-            let xminusoneovere = force_eval!(xminusoneovere);
-            xminusoneovere + 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);
-    }
+    super::generic::rint(x)
 }

src/math/rintf.rs

@@ -9,51 +9,5 @@ pub fn rintf(x: f32) -> f32 {
         args: x,
     }
 
-    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 {
-            #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
-            let x = force_eval!(x);
-            let xplusoneovere = x + one_over_e;
-            #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
-            let xplusoneovere = force_eval!(xplusoneovere);
-            xplusoneovere - one_over_e
-        } else {
-            #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
-            let x = force_eval!(x);
-            let xminusoneovere = x - one_over_e;
-            #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
-            let xminusoneovere = force_eval!(xminusoneovere);
-            xminusoneovere + 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);
-    }
+    super::generic::rint(x)
 }