ulam 0.6.0

Utility crate for ulam calculations.
Documentation 
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use std::{cmp, error::Error};

pub type GreyImage = image::GrayImage; // because ben is british

pub fn generate(x_size: u32, y_size: u32) -> Result<GreyImage, Box<dyn Error>> {
    let mut img = image::ImageBuffer::new(x_size, y_size);
    let total = cmp::max(x_size, y_size).pow(2).try_into()?;
    let sieve = primal::Sieve::new(total);
    let pixel = image::Luma::from([255]);

    for prime in sieve.primes_from(0).take_while(|x| *x <= total) {
        let coord = crate::calc_coord::calc_coord(prime.try_into()?);
        let pos_x: i64 = i64::from(x_size) - i64::from(x_size) / 2 + i64::from(coord.x);
        let pos_y: i64 = i64::from(y_size) / 2 - i64::from(coord.y) + 1;
        if pos_x < 1
            || u32::try_from(pos_x)? > x_size
            || pos_y < 1
            || u32::try_from(pos_y)? > y_size
        {
            // A rectangle is being generated and this prime lies outside it.
            continue;
        }
        img.put_pixel(u32::try_from(pos_x)? - 1, u32::try_from(pos_y)? - 1, pixel);
    }

    Ok(img)
}

// const RED: [u8; 3] = [255, 0, 0];
// const GREEN: [u8; 3] = [0, 255, 0];
// const BLUE: [u8; 3] = [0, 0, 255];

pub fn generate_colour(
    // because Ben is british color is spelled colour.
    x_size: u32,
    y_size: u32,
) -> Result<image::RgbImage, Box<dyn Error>> {
    let mut img = image::RgbImage::new(x_size, y_size);
    let total = cmp::max(x_size, y_size).pow(2).try_into()?;
    let sieve = primal::Sieve::new(total);

    for prime in sieve.primes_from(0).take_while(|x| *x <= total) {
        let coord = crate::calc_coord::calc_coord(prime.try_into()?);
        let pos_x: i64 = i64::from(x_size) - i64::from(x_size) / 2 + i64::from(coord.x);
        let pos_y: i64 = i64::from(y_size) / 2 - i64::from(coord.y) + 1;
        if pos_x < 1
            || u32::try_from(pos_x)? > x_size
            || pos_y < 1
            || u32::try_from(pos_y)? > y_size
        {
            // A rectangle is being generated and this prime lies outside it.
            continue;
        }

        let pixel = image::Rgb(match prime % 6 {
            0 => [255, 0, 0],
            1 => [0, 255, 0],
            3 => [255, 0, 0],
            5 => [0, 0, 255],
            _ => [255, 255, 255],
        });

        img.put_pixel(u32::try_from(pos_x)? - 1, u32::try_from(pos_y)? - 1, pixel);
    }

    Ok(img)
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn check_sq() {
        let odd = generate(5, 5).unwrap();
        let mut expected_odd = image::ImageBuffer::new(5, 5);
        expected_odd.put_pixel(3, 0, image::Luma::from([255_u8]));
        expected_odd.put_pixel(0, 1, image::Luma::from([255_u8]));
        expected_odd.put_pixel(2, 1, image::Luma::from([255_u8]));
        expected_odd.put_pixel(3, 1, image::Luma::from([255_u8]));
        expected_odd.put_pixel(4, 1, image::Luma::from([255_u8]));
        expected_odd.put_pixel(1, 2, image::Luma::from([255_u8]));
        expected_odd.put_pixel(0, 3, image::Luma::from([255_u8]));
        expected_odd.put_pixel(2, 3, image::Luma::from([255_u8]));
        expected_odd.put_pixel(3, 4, image::Luma::from([255_u8]));
        assert_eq!(odd, expected_odd);

        let even = generate(4, 4).unwrap();
        let mut expected_even = image::ImageBuffer::new(4, 4);
        expected_even.put_pixel(2, 0, image::Luma::from([255_u8]));
        expected_even.put_pixel(1, 1, image::Luma::from([255_u8]));
        expected_even.put_pixel(2, 1, image::Luma::from([255_u8]));
        expected_even.put_pixel(3, 1, image::Luma::from([255_u8]));
        expected_even.put_pixel(0, 2, image::Luma::from([255_u8]));
        expected_even.put_pixel(1, 3, image::Luma::from([255_u8]));
        assert_eq!(even, expected_even);
    }
    #[test]
    fn check_bad() {
        let bad = generate(0, 1).unwrap();
        let expected = image::ImageBuffer::new(0, 1);
        assert_eq!(bad, expected);
    }
    #[test]
    #[ignore]
    fn try_generate() {
        generate_colour(1_000, 1_000)
            .unwrap()
            .save("./result.png")
            .unwrap();
    }
    #[test]
    fn check_rect() {
        let tall = generate(5, 3).unwrap();
        let mut expected_tall = image::ImageBuffer::new(5, 3);
        expected_tall.put_pixel(0, 0, image::Luma::from([255_u8]));
        expected_tall.put_pixel(2, 0, image::Luma::from([255_u8]));
        expected_tall.put_pixel(3, 0, image::Luma::from([255_u8]));
        expected_tall.put_pixel(4, 0, image::Luma::from([255_u8]));
        expected_tall.put_pixel(1, 1, image::Luma::from([255_u8]));
        expected_tall.put_pixel(0, 2, image::Luma::from([255_u8]));
        expected_tall.put_pixel(2, 2, image::Luma::from([255_u8]));
        assert_eq!(tall, expected_tall);

        let wide = generate(3, 5).unwrap();
        let mut expected_wide = image::ImageBuffer::new(3, 5);
        expected_wide.put_pixel(2, 0, image::Luma::from([255_u8]));
        expected_wide.put_pixel(1, 1, image::Luma::from([255_u8]));
        expected_wide.put_pixel(2, 1, image::Luma::from([255_u8]));
        expected_wide.put_pixel(0, 2, image::Luma::from([255_u8]));
        expected_wide.put_pixel(1, 3, image::Luma::from([255_u8]));
        expected_wide.put_pixel(2, 4, image::Luma::from([255_u8]));
        assert_eq!(wide, expected_wide);
    }
}