rusty_flac 0.1.0

Pure-Rust FLAC encoder + decoder, no C, no unsafe-by-default deps. Encodes 17% and decodes 23% faster than FFmpeg while producing smaller files on every benchmarked content class; lossless and interoperable both directions.
Documentation 
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//! FLAC's two CRCs (no reflection, init 0), table-driven.
//!
//! CRC-8  poly 0x07  — over the frame header.
//! CRC-16 poly 0x8005 — over the whole frame.

const fn build_crc8_table() -> [u8; 256] {
    let mut table = [0u8; 256];
    let mut i = 0;
    while i < 256 {
        let mut crc = i as u8;
        let mut bit = 0;
        while bit < 8 {
            crc = if crc & 0x80 != 0 {
                (crc << 1) ^ 0x07
            } else {
                crc << 1
            };
            bit += 1;
        }
        table[i] = crc;
        i += 1;
    }
    table
}

const fn build_crc16_table() -> [u16; 256] {
    let mut table = [0u16; 256];
    let mut i = 0;
    while i < 256 {
        let mut crc = (i as u16) << 8;
        let mut bit = 0;
        while bit < 8 {
            crc = if crc & 0x8000 != 0 {
                (crc << 1) ^ 0x8005
            } else {
                crc << 1
            };
            bit += 1;
        }
        table[i] = crc;
        i += 1;
    }
    table
}

const CRC8_TABLE: [u8; 256] = build_crc8_table();
const CRC16_TABLE: [u16; 256] = build_crc16_table();

pub fn crc8(data: &[u8]) -> u8 {
    let mut crc = 0u8;
    for &b in data {
        crc = CRC8_TABLE[(crc ^ b) as usize];
    }
    crc
}

pub fn crc16(data: &[u8]) -> u16 {
    let mut crc = 0u16;
    for &b in data {
        crc = (crc << 8) ^ CRC16_TABLE[((crc >> 8) ^ b as u16) as usize];
    }
    crc
}

#[cfg(test)]
mod tests {
    use super::*;

    /// Bitwise reference implementations (the pre-table originals).
    fn crc8_ref(data: &[u8]) -> u8 {
        let mut crc = 0u8;
        for &b in data {
            crc ^= b;
            for _ in 0..8 {
                crc = if crc & 0x80 != 0 {
                    (crc << 1) ^ 0x07
                } else {
                    crc << 1
                };
            }
        }
        crc
    }

    fn crc16_ref(data: &[u8]) -> u16 {
        let mut crc = 0u16;
        for &b in data {
            crc ^= (b as u16) << 8;
            for _ in 0..8 {
                crc = if crc & 0x8000 != 0 {
                    (crc << 1) ^ 0x8005
                } else {
                    crc << 1
                };
            }
        }
        crc
    }

    #[test]
    fn tables_match_bitwise_reference() {
        let data: Vec<u8> = (0..4096u32).map(|i| (i * 31 + 7) as u8).collect();
        for len in [0, 1, 2, 63, 64, 65, 4096] {
            assert_eq!(crc8(&data[..len]), crc8_ref(&data[..len]), "crc8 len={len}");
            assert_eq!(
                crc16(&data[..len]),
                crc16_ref(&data[..len]),
                "crc16 len={len}"
            );
        }
    }
}