

Task

Demonstrate a method of deriving the Cyclic Redundancy Check from within the language.



The result should be in accordance with ISO 3309, ITU-T V.42, Gzip and PNG.

Algorithms are described on Computation of CRC in Wikipedia.
This variant of CRC-32 uses LSB-first order, sets the initial CRC to FFFFFFFF16, and complements the final CRC.

For the purpose of this task, generate a CRC-32 checksum for the ASCII encoded string:

 The quick brown fox jumps over the lazy dog


 
fn crc32_compute_table() -> [u32; 256] {
    let mut crc32_table = [0; 256];
 
    for n in 0..256 {
        crc32_table[n as usize] = (0..8).fold(n as u32, |acc, _| {
            match acc & 1 {
                1 => 0xedb88320 ^ (acc >> 1),
                _ => acc >> 1,
            }
        });
    }
 
    crc32_table
}
 
fn crc32(buf: &str) -> u32 {
    let crc_table = crc32_compute_table();
 
    !buf.bytes().fold(!0, |acc, octet| {
        (acc >> 8) ^ crc_table[((acc & 0xff) ^ octet as u32) as usize]
    })
}
 
fn main() {
    println!("{:x}", crc32("The quick brown fox jumps over the lazy dog"));
}
 