/*
 * // Copyright (c) Radzivon Bartoshyk 8/2025. All rights reserved.
 * //
 * // Redistribution and use in source and binary forms, with or without modification,
 * // are permitted provided that the following conditions are met:
 * //
 * // 1.  Redistributions of source code must retain the above copyright notice, this
 * // list of conditions and the following disclaimer.
 * //
 * // 2.  Redistributions in binary form must reproduce the above copyright notice,
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 * // and/or other materials provided with the distribution.
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 * // contributors may be used to endorse or promote products derived from
 * // this software without specific prior written permission.
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 * // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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use crate::err::inverff::erfinv_core;

/// Complementary inverse error function
///
/// Max ulp 0.5
pub fn f_erfcinvf(x: f32) -> f32 {
    if x <= 0. {
        if x == 0. {
            return f32::INFINITY;
        }
        return f32::NAN;
    }

    if x >= 1. {
        if x == 1. {
            return 0.;
        }
        if x >= 2. {
            // x > 2
            if x == 2. {
                return f32::NEG_INFINITY;
            }
            return f32::NAN;
        }
    }

    let z = x as f64;
    static SIGN: [f32; 2] = [1.0, -1.0];
    // inferfc(x) = -inverf(1-x)
    // ax doesn't need to be extremely accurate,
    // it's just boundary detection so will do subtraction in f32
    erfinv_core(1. - z, (1. - x).abs().to_bits(), SIGN[(x > 1.) as usize])
}

#[cfg(test)]
mod tests {
    use super::f_erfcinvf;
    #[test]
    fn m_test() {
        assert!(f_erfcinvf(-1.).is_nan());
        assert_eq!(f_erfcinvf(0.), f32::INFINITY);
        assert_eq!(f_erfcinvf(2.), f32::NEG_INFINITY);
        assert!(f_erfcinvf(2.1).is_nan());
        assert_eq!(f_erfcinvf(0.5), 0.47693628);
        assert_eq!(f_erfcinvf(1.5), -0.47693628);
        assert_eq!(f_erfcinvf(0.002), 2.1851242);
        assert_eq!(f_erfcinvf(1.002), -0.0017724329);
    }
}
