#![allow(unreachable_code)]

use core::f64;

const TOINT: f64 = 1. / f64::EPSILON;

/// Ceil (f64)

///

/// Finds the nearest integer greater than or equal to `x`.

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

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

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

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

    // and speed.

    llvm_intrinsically_optimized! {

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

            return unsafe { ::core::intrinsics::ceilf64(x) }

        }

    }

    #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]

    {

        //use an alternative implementation on x86, because the

        //main implementation fails with the x87 FPU used by

        //debian i386, probably due to excess precision issues.

        //basic implementation taken from https://github.com/rust-lang/libm/issues/219

        use super::fabs;

        if fabs(x).to_bits() < 4503599627370496.0_f64.to_bits() {

            let truncated = x as i64 as f64;

            if truncated < x {

                return truncated + 1.0;

            } else {

                return truncated;

            }

        } else {

            return x;

        }

    }

    let u: u64 = x.to_bits();

    let e: i64 = (u >> 52 & 0x7ff) as i64;

    let y: f64;

    if e >= 0x3ff + 52 || x == 0. {

        return x;

    }

    // y = int(x) - x, where int(x) is an integer neighbor of x

    y = if (u >> 63) != 0 { x - TOINT + TOINT - x } else { x + TOINT - TOINT - x };

    // special case because of non-nearest rounding modes

    if e < 0x3ff {

        force_eval!(y);

        return if (u >> 63) != 0 { -0. } else { 1. };

    }

    if y < 0. { x + y + 1. } else { x + y }

}

#[cfg(test)]

mod tests {

    use core::f64::*;

    use super::*;

    #[test]

    fn sanity_check() {

        assert_eq!(ceil(1.1), 2.0);

        assert_eq!(ceil(2.9), 3.0);

    }

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

    #[test]

    fn spec_tests() {

        // Not Asserted: that the current rounding mode has no effect.

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

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

            assert_eq!(ceil(f), f);

        }

    }

}