r2rs-nmath 0.1.1

Statistics programming for Rust based on R's nmath package
Documentation 
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// Translation of nmath's rexp
//
// 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, Positive64, Real64};

use crate::{rng::NMathRNG, traits::RNG};

/// Random variates from the exponential distribution.
pub fn rexp<P: Into<Positive64>, R: RNG>(scale: P, rng: &mut R) -> Real64 {
    let scale = scale.into().unwrap();

    if !scale.is_finite() {
        return f64::nan().into();
    }
    if scale == 0.0 {
        return 0.0.into();
    }

    (scale * rng.exp_rand()).into()
    // --> in ./sexp.c
}