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Use a series expansion for cosine

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This commit is contained in:
Stephen Marz 2020-05-24 10:06:15 -04:00
parent 56ae6230dd
commit 43abdd358f
1 changed files with 28 additions and 3 deletions
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31
risc_v/src/gpu.rs
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@ -325,7 +325,7 @@ pub fn stroke_rect(dev: &mut Device, rect: Rect, color: Pixel, size: u32) {
), color);
}
fn mycos(angle_degrees: f64) -> f64 {
fn look_mycos(angle_degrees: f64) -> f64 {
const COS_TABLE: [f64; 73] = [
1.0,
0.9962,
@ -404,6 +404,31 @@ fn mycos(angle_degrees: f64) -> f64 {
let lookup_ang = angle_degrees as usize / 5;
COS_TABLE[lookup_ang % COS_TABLE.len()]
}
fn fmod(x: f64, y: f64) -> f64 {
let x = x as i64;
let y = y as i64;
(x - x / y * y) as f64
}
fn mycos(angle_degrees: f64) -> f64 {
let angle_mod_360 = fmod(angle_degrees, 360.0);
let x = 3.14159265359 * angle_mod_360 / 180.0;
let mut result = 1.0;
let mut inter = 1.0;
let num = x * x;
for i in 1..=10 {
let comp = 2.0 * i as f64;
let den = comp * (comp - 1.0);
inter *= num / den;
if i % 2 == 0 {
result += inter;
}
else {
result -= inter;
}
}
result
}
fn mysin(angle_degrees: f64) -> f64 {
mycos(90.0 - angle_degrees)
@ -412,13 +437,13 @@ fn mysin(angle_degrees: f64) -> f64 {
pub fn draw_cosine(dev: &mut Device, rect: Rect, color: Pixel) {
for x in 1..=(rect.width-rect.x) {
let fx = x as f64;
let fy = 1.0 - mycos(fx);
let fy = -mycos(fx);
let y = ((fy * rect.height as f64) as i32 + rect.y as i32) as u32;
// println!("cos({}) is {}, gives y: {}", fx, fy, y);
fill_rect(dev, Rect::new(
rect.x + x,
y,
10, 10
1, 1
), color);
}
}