r2rs-nmath 0.1.1

Statistics programming for Rust based on R's nmath package
Documentation 
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// Translation of nmath's qsignrank
//
// Copyright (C) 2020 neek-sss
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

use num_traits::Float;
use strafe_type::{FloatConstraint, LogProbability64, Natural64, Probability64, Real64};

use crate::{distribution::signrank::csignrank, traits::DPQ};

pub fn qsignrank<P: Into<Probability64>, N: Into<Natural64>>(
    x: P,
    n: N,
    lower_tail: bool,
) -> Real64 {
    let x = x.into().unwrap();
    qsignrank_inner(x, n, lower_tail, false)
}

pub fn log_qsignrank<LP: Into<LogProbability64>, N: Into<Natural64>>(
    x: LP,
    n: N,
    lower_tail: bool,
) -> Real64 {
    let x = x.into().unwrap();
    qsignrank_inner(x, n, lower_tail, true)
}

fn qsignrank_inner<N: Into<Natural64>>(mut x: f64, n: N, lower_tail: bool, log: bool) -> Real64 {
    let mut n = n.into().unwrap();

    let mut f = 0.0;
    let mut p = 0.0;

    if !x.is_finite() || !n.is_finite() {
        return f64::nan().into();
    }

    n = n.round();

    if x == f64::dt_0(lower_tail, log) {
        return 0.0.into();
    }
    if x == f64::dt_1(lower_tail, log) {
        return (n * (n + 1.0) / 2.0).into();
    }

    if log || !lower_tail {
        /* lower_tail,non-log "p" */
        x = x.dt_qiv(lower_tail, log);
    }

    let nn = n as i32;
    f = (-n * std::f64::consts::LN_2).exp();
    p = 0.0;
    let mut q = 0;
    if x <= 0.5 {
        x = x - 10.0 * 2.2204460492503131e-16;
        loop {
            p += csignrank(q, nn) * f;
            if p >= x {
                break;
            }
            q += 1
        }
    } else {
        x = 1.0 - x + 10.0 * 2.2204460492503131e-16;
        loop {
            p += csignrank(q, nn) * f;
            if p > x {
                q = (n * (n + 1.0) / 2.0 - q as f64) as i32;
                break;
            } else {
                q += 1
            }
        }
    }

    q.into()
}