1 files changed, 151 insertions, 0 deletions
diff --git a/library/compiler-builtins/libm/src/math/generic/floor.rs b/library/compiler-builtins/libm/src/math/generic/floor.rs
new file mode 100644
index 00000000000..2438046254f
--- /dev/null
+++ b/library/compiler-builtins/libm/src/math/generic/floor.rs
@@ -0,0 +1,151 @@
+/* SPDX-License-Identifier: MIT
+ * origin: musl src/math/floor.c */
+
+//! Generic `floor` algorithm.
+//!
+//! Note that this uses the algorithm from musl's `floorf` rather than `floor` or `floorl` because
+//! performance seems to be better (based on icount) and it does not seem to experience rounding
+//! errors on i386.
+
+use super::super::support::{FpResult, Status};
+use super::super::{Float, Int, IntTy, MinInt};
+
+#[inline]
+pub fn floor<F: Float>(x: F) -> F {
+    floor_status(x).val
+}
+
+#[inline]
+pub fn floor_status<F: Float>(x: F) -> FpResult<F> {
+    let zero = IntTy::<F>::ZERO;
+
+    let mut ix = x.to_bits();
+    let e = x.exp_unbiased();
+
+    // If the represented value has no fractional part, no truncation is needed.
+    if e >= F::SIG_BITS as i32 {
+        return FpResult::ok(x);
+    }
+
+    let status;
+    let res = if e >= 0 {
+        // |x| >= 1.0
+        let m = F::SIG_MASK >> e.unsigned();
+        if ix & m == zero {
+            // Portion to be masked is already zero; no adjustment needed.
+            return FpResult::ok(x);
+        }
+
+        // Otherwise, raise an inexact exception.
+        status = Status::INEXACT;
+
+        if x.is_sign_negative() {
+            ix += m;
+        }
+
+        ix &= !m;
+        F::from_bits(ix)
+    } else {
+        // |x| < 1.0, raise an inexact exception since truncation will happen.
+        if ix & F::SIG_MASK == F::Int::ZERO {
+            status = Status::OK;
+        } else {
+            status = Status::INEXACT;
+        }
+
+        if x.is_sign_positive() {
+            // 0.0 <= x < 1.0; rounding down goes toward +0.0.
+            F::ZERO
+        } else if ix << 1 != zero {
+            // -1.0 < x < 0.0; rounding down goes toward -1.0.
+            F::NEG_ONE
+        } else {
+            // -0.0 remains unchanged
+            x
+        }
+    };
+
+    FpResult::new(res, status)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::support::Hexf;
+
+    /// Test against https://en.cppreference.com/w/cpp/numeric/math/floor
+    fn spec_test<F: Float>(cases: &[(F, F, Status)]) {
+        let roundtrip = [F::ZERO, F::ONE, F::NEG_ONE, F::NEG_ZERO, F::INFINITY, F::NEG_INFINITY];
+
+        for x in roundtrip {
+            let FpResult { val, status } = floor_status(x);
+            assert_biteq!(val, x, "{}", Hexf(x));
+            assert_eq!(status, Status::OK, "{}", Hexf(x));
+        }
+
+        for &(x, res, res_stat) in cases {
+            let FpResult { val, status } = floor_status(x);
+            assert_biteq!(val, res, "{}", Hexf(x));
+            assert_eq!(status, res_stat, "{}", Hexf(x));
+        }
+    }
+
+    /* Skipping f16 / f128 "sanity_check"s and spec cases due to rejected literal lexing at MSRV */
+
+    #[test]
+    #[cfg(f16_enabled)]
+    fn spec_tests_f16() {
+        let cases = [];
+        spec_test::<f16>(&cases);
+    }
+
+    #[test]
+    fn sanity_check_f32() {
+        assert_eq!(floor(0.5f32), 0.0);
+        assert_eq!(floor(1.1f32), 1.0);
+        assert_eq!(floor(2.9f32), 2.0);
+    }
+
+    #[test]
+    fn spec_tests_f32() {
+        let cases = [
+            (0.1, 0.0, Status::INEXACT),
+            (-0.1, -1.0, Status::INEXACT),
+            (0.9, 0.0, Status::INEXACT),
+            (-0.9, -1.0, Status::INEXACT),
+            (1.1, 1.0, Status::INEXACT),
+            (-1.1, -2.0, Status::INEXACT),
+            (1.9, 1.0, Status::INEXACT),
+            (-1.9, -2.0, Status::INEXACT),
+        ];
+        spec_test::<f32>(&cases);
+    }
+
+    #[test]
+    fn sanity_check_f64() {
+        assert_eq!(floor(1.1f64), 1.0);
+        assert_eq!(floor(2.9f64), 2.0);
+    }
+
+    #[test]
+    fn spec_tests_f64() {
+        let cases = [
+            (0.1, 0.0, Status::INEXACT),
+            (-0.1, -1.0, Status::INEXACT),
+            (0.9, 0.0, Status::INEXACT),
+            (-0.9, -1.0, Status::INEXACT),
+            (1.1, 1.0, Status::INEXACT),
+            (-1.1, -2.0, Status::INEXACT),
+            (1.9, 1.0, Status::INEXACT),
+            (-1.9, -2.0, Status::INEXACT),
+        ];
+        spec_test::<f64>(&cases);
+    }
+
+    #[test]
+    #[cfg(f128_enabled)]
+    fn spec_tests_f128() {
+        let cases = [];
+        spec_test::<f128>(&cases);
+    }
+}