trig-const

Rust implementation of const trig functions.

The majority of functions have been implemented using a modified version of libm for const Rust.

This implementation carries forward the original MIT license.

Project Goals

• Correctness while const (same result as std within a rounding error)
• no-std
• No unsafe

Requirements

This crate supports any compiler version back to rustc 1.85.0

[dependencies]
trig-const = "0"

Example

use std::f64::consts::PI;
use trig_const::cos;

const COS_PI: f64 = cos(PI);
assert_eq!(COS_PI, -1.0);

use std::f64::consts::PI;
use trig_const::{atan2, cos, sin};

/// 45° in radians
const DEG_45: f64 = 45.0 * PI / 180.0;

/// Pre-computed matrix to rotate object 45°
const ROTATIONAL_MATRIX: [[f64; 3]; 3] = [
    [cos(DEG_45), 0.0, sin(DEG_45)],
    [0.0, 1.0, 0.0],
    [-sin(DEG_45), 0.0, cos(DEG_45)],
];

/// atan2 calculation
const ATAN2_0_0: f64 = atan2(0.0, 0.0);

fn main() {
    println!("{:?}", ROTATIONAL_MATRIX);
    println!("{}", ATAN2_0_0);
}

Precision

Precision will be different platform to platform. There is a precision comparison within examples, under examples/std_cmp.rs (to run: cargo run --release --example std_cmp).

On aarch64, I get:

Func	Total Tests	Diff Count	Max Diff
acos	2000000	349419	4.44089e-16
acosh	99000001	8505318	8.88178e-16
asin	2000000	173790	2.22045e-16
asinh	99000001	8714913	8.88178e-16
atan	50265483	3290826	2.22045e-16
atanh	1999998	771064	3.34115e-11
cos	50265483	2173339	1.11022e-16
cosh	25132742	6498663	2.91038e-11
ln	99999001	3413955	8.88178e-16
exp	20000001	1944323	3.63798e-12
fabs	20000001	0	0.00000e0
floor	20000001	0	0.00000e0
sin	50265483	2255609	1.11022e-16
sinh	25132742	7200641	2.91038e-11
sqrt	10000001	2500953	4.44089e-16
tan	50265483	20777207	3.72529e-9

History

This crate was originally implemented using trigonometric Taylor series approximations, inspired by the work of Dr. Austin Henley and Dr. Stephen Marz:

• GitHub Repo: https://github.com/AZHenley/cosine
• Article: https://austinhenley.com/blog/cosine.html

However, several functions have since been implemented using a modified version of libm for const Rust which improved precision.