Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Binomial sampling: limit max n and use powi #752

Merged
merged 1 commit into from Mar 7, 2019
Merged

Binomial sampling: limit max n and use powi #752

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Jump to
Jump to file
Failed to load files.
Diff view
Diff view
29 changes: 2 additions & 27 deletions src/distributions/binomial.rs
View file
Open in desktop
Expand Up @@ -47,31 +47,6 @@ impl Binomial {
}
}

/// Raise a `base` to the power of `exp`, using exponentiation by squaring.
///
/// This implementation is based on the one in the `num_traits` crate. It is
/// slightly modified to accept `u64` exponents.
fn pow(mut base: f64, mut exp: u64) -> f64 {
if exp == 0 {
return 1.;
}

while exp & 1 == 0 {
base *= base;
exp >>= 1;
}

let mut acc = base;
while exp > 1 {
exp >>= 1;
base *= base;
if exp & 1 == 1 {
acc *= base;
}
}
acc
}

impl Distribution<u64> for Binomial {
fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> u64 {
// Handle these values directly.
Expand All @@ -98,11 +73,11 @@ impl Distribution<u64> for Binomial {
// Voratas Kachitvichyanukul and Bruce W. Schmeiser. 1988. Binomial
// random variate generation. Commun. ACM 31, 2 (February 1988),
// 216-222. http://dx.doi.org/10.1145/42372.42381
if (self.n as f64) * p < 10. {
if (self.n as f64) * p < 10. && self.n <= (::std::i32::MAX as u64) {
let q = 1. - p;
let s = p / q;
let a = ((self.n + 1) as f64) * s;
let mut r = pow(q, self.n);
let mut r = q.powi(self.n as i32);
let mut u: f64 = rng.gen();
let mut x = 0;
while u > r as f64 {
Expand Down