Trait dashu_float::ops::EstimatedLog2

source · 
pub trait EstimatedLog2 {
    fn log2_bounds(&self) -> (f32, f32);

    fn log2_est(&self) -> f32 { ... }
}
Expand description

Fast estimation of the binary logarithm of a number

Panics

Panics if the number is 0

Examples

use dashu_base::EstimatedLog2;

let lb3 = 1.584962500721156f32;
let (lb3_lb, lb3_ub) = 3u8.log2_bounds();
assert!(lb3_lb <= lb3 && lb3 <= lb3_ub);
assert!((lb3 - lb3_lb) / lb3 < 1. / 256.);
assert!((lb3_ub - lb3) / lb3 <= 1. / 256.);

let lb3_est = 3u8.log2_est();
assert!((lb3 - lb3_est).abs() < 1e-3);

Required Methods§

Estimate the bounds of the binary logarithm.

The result is (lower bound, upper bound) such that lower bound ≤ log2(self) ≤ upper bound. The precision of the bounds must be at least 8 bits (relative error < 2^-8).

With std disabled, the precision is about 13 bits. With std enabled, the precision can be full 24 bits. But the exact precision is not guaranteed and should not be not relied on.

For negative values, the logarithm is calculated based on its absolute value. If the number is zero, then negative infinity will be returned.

Provided Methods§

Estimate the value of the binary logarithm. It’s calculated as the average of log2_bounds by default.

Implementations on Foreign Types§

Implementors§