Trait dashu_int::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

Required Methods

source

fn log2_bounds(&self) -> (f32, f32)

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 is at least 8 bits (relative error < 2^-8).

With std disabled, the precision is about 13 bits. With std enabled, the precision will be full 23 bits.

For negative values, the logarithm is calculated based on its absolute value.

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.);