Test sinf and cosf kernels f32 vs f64 with relative

main.rs

//
// Sin functions
//
const S1: f64 = -0.166666666416265235595; /* -0x15555554cbac77.0p-55 */
const S2: f64 = 0.0083333293858894631756; /*  0x111110896efbb2.0p-59 */
const S3: f64 = -0.000198393348360966317347; /* -0x1a00f9e2cae774.0p-65 */
const S4: f64 = 0.0000027183114939898219064; /*  0x16cd878c3b46a7.0p-71 */

pub fn k_sinf(x: f64) -> f32 {
    let z = x * x;
    let w = z * z;
    let r = S3 + z * S4;
    let s = z * x;
    ((x + s * (S1 + z * S2)) + s * w * r) as f32
}

const S1_F32: f32 = -0.166666666416265235595; /* -0x15555554cbac77.0p-55 */
const S2_F32: f32 = 0.0083333293858894631756; /*  0x111110896efbb2.0p-59 */
const S3_F32: f32 = -0.000198393348360966317347; /* -0x1a00f9e2cae774.0p-65 */
const S4_F32: f32 = 0.0000027183114939898219064; /*  0x16cd878c3b46a7.0p-71 */

fn k_sinf_f32(x: f32) -> f32 {
    let z = x * x;
    let w = z * z;
    let r = S3_F32 + z * S4_F32;
    let s = z * x;
    ((x + s * (S1_F32 + z * S2_F32)) + s * w * r)
}

// Cos functinos
const C0: f64 = -0.499999997251031003120; /* -0x1ffffffd0c5e81.0p-54 */
const C1: f64 = 0.0416666233237390631894; /*  0x155553e1053a42.0p-57 */
const C2: f64 = -0.00138867637746099294692; /* -0x16c087e80f1e27.0p-62 */
const C3: f64 = 0.0000243904487962774090654; /*  0x199342e0ee5069.0p-68 */

pub fn k_cosf(x: f64) -> f32 {
    let z = x * x;
    let w = z * z;
    let r = C2 + z * C3;
    (((1.0 + z * C0) + w * C1) + (w * z) * r) as f32
}

const C0_F32: f32 = -0.499999997251031003120; /* -0x1ffffffd0c5e81.0p-54 */
const C1_F32: f32 = 0.0416666233237390631894; /*  0x155553e1053a42.0p-57 */
const C2_F32: f32 = -0.00138867637746099294692; /* -0x16c087e80f1e27.0p-62 */
const C3_F32: f32 = 0.0000243904487962774090654; /*  0x199342e0ee5069.0p-68 */

pub fn k_cosf_f32(x: f32) -> f32 {
    let z = x * x;
    let w = z * z;
    let r = C2_F32 + z * C3_F32;
    (((1.0 + z * C0_F32) + w * C1_F32) + (w * z) * r) as f32
}

use std::f32::consts::PI;

fn main() {
    let mut max_error_sin: f32 = 0.0;
    let mut max_error_cos: f32 = 0.0;

    let mut max_rel_error_sin: f32 = 0.0;
    let mut max_rel_error_cos: f32 = 0.0;

    for n in 0..100000001 {
        let input = PI / 4.0 / 100000000.0 * n as f32;

        let high_prec_sin = k_sinf(input as f64);
        let low_prec_sin = k_sinf_f32(input);

        let error_sin = (high_prec_sin - low_prec_sin).abs();
        let error_rel_sin = ((high_prec_sin - low_prec_sin) / high_prec_sin).abs();

        max_error_sin = max_error_sin.max(error_sin);
        max_rel_error_sin = max_rel_error_sin.max(error_rel_sin);
    }

    for n in -100000000..100000001 {
        let input = PI / 4.0 / 100000000.0 * n as f32;

        let high_prec_cos = k_cosf(input as f64);
        let low_prec_cos = k_cosf_f32(input);

        let error_cos = (high_prec_cos - low_prec_cos).abs();
        let error_rel_cos = ((high_prec_cos - low_prec_cos) / high_prec_cos).abs();

        max_error_cos = max_error_cos.max(error_cos);
        max_rel_error_cos = max_rel_error_cos.max(error_rel_cos);

        //println!("Error for input {} = {}", input, error);
    }

    println!("Max error sin = {}", max_error_sin);
    println!("Max error cos = {}", max_error_cos);
    println!("Max relative error sin = {}", max_rel_error_sin);
    println!("Max relative error cos = {}", max_rel_error_cos);