sparse_strips/vello_common/src/math.rs

// Copyright 2025 the Vello Authors
// SPDX-License-Identifier: Apache-2.0 OR MIT

//! Mathematical helper functions.

#[cfg(not(feature = "std"))]
use peniko::kurbo::common::FloatFuncs as _;

// See https://raphlinus.github.io/audio/2018/09/05/sigmoid.html for a little
// explanation of this approximation to the erf function.
/// Approximate the erf function.
pub fn compute_erf7(x: f32) -> f32 {
    let x = x * core::f32::consts::FRAC_2_SQRT_PI;
    let xx = x * x;
    let x = x + (0.24295 + (0.03395 + 0.0104 * xx) * xx) * (x * xx);
    x / (1.0 + x * x).sqrt()
}