use core::u64;

/// Absolute value (magnitude) (f64)

/// Calculates the absolute value (magnitude) of the argument `x`,

/// by direct manipulation of the bit representation of `x`.

#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]

pub fn fabs(x: f64) -> f64 {

    // On wasm32 we know that LLVM's intrinsic will compile to an optimized

    // `f64.abs` native instruction, so we can leverage this for both code size

    // and speed.

    llvm_intrinsically_optimized! {

        #[cfg(target_arch = "wasm32")] {

            return unsafe { ::core::intrinsics::fabsf64(x) }

        }

    }

    f64::from_bits(x.to_bits() & (u64::MAX / 2))

}

#[cfg(test)]

mod tests {

    use core::f64::*;

    use super::*;

    #[test]

    fn sanity_check() {

        assert_eq!(fabs(-1.0), 1.0);

        assert_eq!(fabs(2.8), 2.8);

    }

    /// The spec: https://en.cppreference.com/w/cpp/numeric/math/fabs

    #[test]

    fn spec_tests() {

        assert!(fabs(NAN).is_nan());

        for f in [0.0, -0.0].iter().copied() {

            assert_eq!(fabs(f), 0.0);

        }

        for f in [INFINITY, NEG_INFINITY].iter().copied() {

            assert_eq!(fabs(f), INFINITY);

        }

    }

}