blurhash 0.2.2

A pure Rust implementation of blurhash
Documentation 
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use std::io::Write;

/// srgb 0-255 integer to linear 0.0-1.0 floating point conversion.
pub fn srgb_to_linear(value: u8) -> f32 {
    let v = value as f32 / 255.;
    if v <= 0.04045 {
        v / 12.92
    } else {
        f32::powf((v + 0.055) / 1.055, 2.4)
    }
}

fn generate_srgb_lookup() -> [f32; 256] {
    let mut table = [0f32; 256];
    for (i, val) in table.iter_mut().enumerate() {
        *val = srgb_to_linear(i as u8);
    }
    table
}

fn write_srgb(f: &mut std::fs::File) {
    let table = generate_srgb_lookup();
    writeln!(f, "static SRGB_LOOKUP: [f32; 256] = {:?};", table).unwrap();
}

fn write_base83(f: &mut std::fs::File) {
    const CHARACTERS: &[u8; 83] =
        b"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~";
    writeln!(f, "const CHARACTERS: [u8; 83] = {:?};", CHARACTERS).unwrap();

    let max_plus_one = CHARACTERS.iter().max().unwrap() + 1;
    let mut inv_map: [u8; 256] = [max_plus_one; 256];
    for (i, &c) in CHARACTERS.iter().enumerate() {
        inv_map[c as usize] = i as u8;
    }
    writeln!(
        f,
        "const CHARACTERS_INV: [u8; {max_plus_one}] = {:?};",
        &inv_map[0..max_plus_one as usize]
    )
    .unwrap();
    writeln!(f, "const CHARACTERS_INV_INVALID: u8 = {};", max_plus_one).unwrap();
}

fn main() {
    let out_dir = std::env::var("OUT_DIR").unwrap();
    let out_dir = std::path::PathBuf::from(out_dir);

    let mut f = std::fs::File::create(out_dir.join("srgb_lookup.rs")).unwrap();
    write_srgb(&mut f);

    let mut f = std::fs::File::create(out_dir.join("base83_lookup.rs")).unwrap();
    write_base83(&mut f);
}