claxon/
crc.rs

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// Claxon -- A FLAC decoding library in Rust
// Copyright 2014 Ruud van Asseldonk
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// A copy of the License has been included in the root of the repository.

use std::io;
use input::ReadBytes;

// These tables were taken from the tables in crc.c in libflac.

const CRC8_TABLE: [u8; 256] =
    [0x00, 0x07, 0x0e, 0x09, 0x1c, 0x1b, 0x12, 0x15, 0x38, 0x3f, 0x36, 0x31, 0x24, 0x23, 0x2a,
     0x2d, 0x70, 0x77, 0x7e, 0x79, 0x6c, 0x6b, 0x62, 0x65, 0x48, 0x4f, 0x46, 0x41, 0x54, 0x53,
     0x5a, 0x5d, 0xe0, 0xe7, 0xee, 0xe9, 0xfc, 0xfb, 0xf2, 0xf5, 0xd8, 0xdf, 0xd6, 0xd1, 0xc4,
     0xc3, 0xca, 0xcd, 0x90, 0x97, 0x9e, 0x99, 0x8c, 0x8b, 0x82, 0x85, 0xa8, 0xaf, 0xa6, 0xa1,
     0xb4, 0xb3, 0xba, 0xbd, 0xc7, 0xc0, 0xc9, 0xce, 0xdb, 0xdc, 0xd5, 0xd2, 0xff, 0xf8, 0xf1,
     0xf6, 0xe3, 0xe4, 0xed, 0xea, 0xb7, 0xb0, 0xb9, 0xbe, 0xab, 0xac, 0xa5, 0xa2, 0x8f, 0x88,
     0x81, 0x86, 0x93, 0x94, 0x9d, 0x9a, 0x27, 0x20, 0x29, 0x2e, 0x3b, 0x3c, 0x35, 0x32, 0x1f,
     0x18, 0x11, 0x16, 0x03, 0x04, 0x0d, 0x0a, 0x57, 0x50, 0x59, 0x5e, 0x4b, 0x4c, 0x45, 0x42,
     0x6f, 0x68, 0x61, 0x66, 0x73, 0x74, 0x7d, 0x7a, 0x89, 0x8e, 0x87, 0x80, 0x95, 0x92, 0x9b,
     0x9c, 0xb1, 0xb6, 0xbf, 0xb8, 0xad, 0xaa, 0xa3, 0xa4, 0xf9, 0xfe, 0xf7, 0xf0, 0xe5, 0xe2,
     0xeb, 0xec, 0xc1, 0xc6, 0xcf, 0xc8, 0xdd, 0xda, 0xd3, 0xd4, 0x69, 0x6e, 0x67, 0x60, 0x75,
     0x72, 0x7b, 0x7c, 0x51, 0x56, 0x5f, 0x58, 0x4d, 0x4a, 0x43, 0x44, 0x19, 0x1e, 0x17, 0x10,
     0x05, 0x02, 0x0b, 0x0c, 0x21, 0x26, 0x2f, 0x28, 0x3d, 0x3a, 0x33, 0x34, 0x4e, 0x49, 0x40,
     0x47, 0x52, 0x55, 0x5c, 0x5b, 0x76, 0x71, 0x78, 0x7f, 0x6a, 0x6d, 0x64, 0x63, 0x3e, 0x39,
     0x30, 0x37, 0x22, 0x25, 0x2c, 0x2b, 0x06, 0x01, 0x08, 0x0f, 0x1a, 0x1d, 0x14, 0x13, 0xae,
     0xa9, 0xa0, 0xa7, 0xb2, 0xb5, 0xbc, 0xbb, 0x96, 0x91, 0x98, 0x9f, 0x8a, 0x8d, 0x84, 0x83,
     0xde, 0xd9, 0xd0, 0xd7, 0xc2, 0xc5, 0xcc, 0xcb, 0xe6, 0xe1, 0xe8, 0xef, 0xfa, 0xfd, 0xf4,
     0xf3];

const CRC16_TABLE: [u16; 256] =
    [0x0000, 0x8005, 0x800f, 0x000a, 0x801b, 0x001e, 0x0014, 0x8011, 0x8033, 0x0036, 0x003c,
     0x8039, 0x0028, 0x802d, 0x8027, 0x0022, 0x8063, 0x0066, 0x006c, 0x8069, 0x0078, 0x807d,
     0x8077, 0x0072, 0x0050, 0x8055, 0x805f, 0x005a, 0x804b, 0x004e, 0x0044, 0x8041, 0x80c3,
     0x00c6, 0x00cc, 0x80c9, 0x00d8, 0x80dd, 0x80d7, 0x00d2, 0x00f0, 0x80f5, 0x80ff, 0x00fa,
     0x80eb, 0x00ee, 0x00e4, 0x80e1, 0x00a0, 0x80a5, 0x80af, 0x00aa, 0x80bb, 0x00be, 0x00b4,
     0x80b1, 0x8093, 0x0096, 0x009c, 0x8099, 0x0088, 0x808d, 0x8087, 0x0082, 0x8183, 0x0186,
     0x018c, 0x8189, 0x0198, 0x819d, 0x8197, 0x0192, 0x01b0, 0x81b5, 0x81bf, 0x01ba, 0x81ab,
     0x01ae, 0x01a4, 0x81a1, 0x01e0, 0x81e5, 0x81ef, 0x01ea, 0x81fb, 0x01fe, 0x01f4, 0x81f1,
     0x81d3, 0x01d6, 0x01dc, 0x81d9, 0x01c8, 0x81cd, 0x81c7, 0x01c2, 0x0140, 0x8145, 0x814f,
     0x014a, 0x815b, 0x015e, 0x0154, 0x8151, 0x8173, 0x0176, 0x017c, 0x8179, 0x0168, 0x816d,
     0x8167, 0x0162, 0x8123, 0x0126, 0x012c, 0x8129, 0x0138, 0x813d, 0x8137, 0x0132, 0x0110,
     0x8115, 0x811f, 0x011a, 0x810b, 0x010e, 0x0104, 0x8101, 0x8303, 0x0306, 0x030c, 0x8309,
     0x0318, 0x831d, 0x8317, 0x0312, 0x0330, 0x8335, 0x833f, 0x033a, 0x832b, 0x032e, 0x0324,
     0x8321, 0x0360, 0x8365, 0x836f, 0x036a, 0x837b, 0x037e, 0x0374, 0x8371, 0x8353, 0x0356,
     0x035c, 0x8359, 0x0348, 0x834d, 0x8347, 0x0342, 0x03c0, 0x83c5, 0x83cf, 0x03ca, 0x83db,
     0x03de, 0x03d4, 0x83d1, 0x83f3, 0x03f6, 0x03fc, 0x83f9, 0x03e8, 0x83ed, 0x83e7, 0x03e2,
     0x83a3, 0x03a6, 0x03ac, 0x83a9, 0x03b8, 0x83bd, 0x83b7, 0x03b2, 0x0390, 0x8395, 0x839f,
     0x039a, 0x838b, 0x038e, 0x0384, 0x8381, 0x0280, 0x8285, 0x828f, 0x028a, 0x829b, 0x029e,
     0x0294, 0x8291, 0x82b3, 0x02b6, 0x02bc, 0x82b9, 0x02a8, 0x82ad, 0x82a7, 0x02a2, 0x82e3,
     0x02e6, 0x02ec, 0x82e9, 0x02f8, 0x82fd, 0x82f7, 0x02f2, 0x02d0, 0x82d5, 0x82df, 0x02da,
     0x82cb, 0x02ce, 0x02c4, 0x82c1, 0x8243, 0x0246, 0x024c, 0x8249, 0x0258, 0x825d, 0x8257,
     0x0252, 0x0270, 0x8275, 0x827f, 0x027a, 0x826b, 0x026e, 0x0264, 0x8261, 0x0220, 0x8225,
     0x822f, 0x022a, 0x823b, 0x023e, 0x0234, 0x8231, 0x8213, 0x0216, 0x021c, 0x8219, 0x0208,
     0x820d, 0x8207, 0x0202];

/// A reader that computes the CRC-8 over everything it reads.
///
/// The polynomial used is x^8 + x^2 + x^1 + x^0, and the initial value is 0.
pub struct Crc8Reader<R: ReadBytes> {
    inner: R,
    state: u8,
}

/// A reader that computes the CRC-16 over everything it reads.
///
/// The polynomial used is x^16 + x^15 + x^2 + x^0, and the initial value is 0.
pub struct Crc16Reader<R: ReadBytes> {
    inner: R,
    state: u16,
}

impl<R: ReadBytes> Crc8Reader<R> {
    /// Wraps the reader with a CRC-8 computing reader with initial value 0.
    pub fn new(inner: R) -> Crc8Reader<R> {
        Crc8Reader {
            inner: inner,
            state: 0,
        }
    }

    /// Returns the CRC computed thus far.
    pub fn crc(&self) -> u8 {
        self.state
    }

    #[inline(always)]
    fn update_state(&mut self, byte: u8) {
        self.state = CRC8_TABLE[(self.state ^ byte) as usize];
    }
}

impl<R: ReadBytes> Crc16Reader<R> {
    /// Wraps the reader with a CRC-16 computing reader with initial value 0.
    pub fn new(inner: R) -> Crc16Reader<R> {
        Crc16Reader {
            inner: inner,
            state: 0,
        }
    }

    /// Returns the CRC computed thus far.
    pub fn crc(&self) -> u16 {
        self.state
    }

    #[inline(always)]
    fn update_state(&mut self, byte: u8) {
        self.state = (self.state << 8) ^ CRC16_TABLE[((self.state >> 8) as u8 ^ byte) as usize];
    }
}

impl<R: ReadBytes> ReadBytes for Crc8Reader<R> {
    #[inline(always)]
    fn read_u8(&mut self) -> io::Result<u8> {
        match self.inner.read_u8() {
            Ok(byte) => {
                self.update_state(byte);
                Ok(byte)
            },
            Err(err) => Err(err),
        }
    }

    fn read_u8_or_eof(&mut self) -> io::Result<Option<u8>> {
        match self.inner.read_u8_or_eof() {
            Ok(Some(byte)) => {
                self.update_state(byte);
                Ok(Some(byte))
            },
            Ok(None) => Ok(None),
            Err(err) => Err(err),
        }
    }

    fn read_into(&mut self, _buffer: &mut [u8]) -> io::Result<()> {
        panic!("CRC reader does not support read_into.");
    }

    fn skip(&mut self, _amount: u32) -> io::Result<()> {
        panic!("CRC reader does not support skip, it does not compute CRC over skipped data.");
    }
}

impl<R: ReadBytes> ReadBytes for Crc16Reader<R> {
    #[inline(always)]
    fn read_u8(&mut self) -> io::Result<u8> {
        match self.inner.read_u8() {
            Ok(byte) => {
                self.update_state(byte);
                Ok(byte)
            },
            Err(err) => Err(err),
        }
    }

    fn read_u8_or_eof(&mut self) -> io::Result<Option<u8>> {
        match self.inner.read_u8_or_eof() {
            Ok(Some(byte)) => {
                self.update_state(byte);
                Ok(Some(byte))
            },
            Ok(None) => Ok(None),
            Err(err) => Err(err),
        }
    }

    fn read_into(&mut self, _buffer: &mut [u8]) -> io::Result<()> {
        panic!("CRC reader does not support read_into.");
    }

    fn skip(&mut self, _amount: u32) -> io::Result<()> {
        panic!("CRC reader does not support skip, it does not compute CRC over skipped data.");
    }
}

#[cfg(test)]
fn verify_crc8(test_vector: Vec<u8>, result: u8) {
    use input::BufferedReader;
    let data = BufferedReader::new(io::Cursor::new(test_vector));
    let mut reader = Crc8Reader::new(data);
    while let Some(_) = reader.read_u8_or_eof().unwrap() {}
    assert_eq!(reader.crc(), result);
}

#[cfg(test)]
fn verify_crc16(test_vector: Vec<u8>, result: u16) {
    use input::BufferedReader;
    let data = BufferedReader::new(io::Cursor::new(test_vector));
    let mut reader = Crc16Reader::new(data);
    while let Some(_) = reader.read_u8_or_eof().unwrap() {}
    assert_eq!(reader.crc(), result);
}

#[test]
fn verify_crc8_test_vectors() {
    verify_crc8(vec![0x1f], 0x5d);
    verify_crc8(vec![0x04, 0x01], 0x53);
    verify_crc8(vec![0x61, 0x62, 0x63], 0x5f);
}

#[test]
fn verify_crc16_test_vectors() {
    verify_crc16(vec![0x1f], 0x8041);
    verify_crc16(vec![0x04, 0x01], 0x1806);
    verify_crc16(vec![0x61, 0x62, 0x63], 0xcadb);
}