sdmmc-core 0.5.0

SD/MMC core data structures and algorithms
Documentation 
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const CRC16_POLY: u16 = 0b0001_0000_0010_0001;

/// Represents the 16-bit CRC used to protect SD memory card commands, responses, and data transfer messages.
#[repr(C)]
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Crc16(u16);

impl Crc16 {
    /// Creates a new [Crc16].
    pub const fn new() -> Self {
        Self(0)
    }

    /// Gets the inner representation of the [Crc16] bits.
    pub const fn bits(&self) -> u16 {
        self.0
    }

    /// Calculates the CRC7 value according the algorithm defined in the simplified physical specification.
    /// See section "4.5 Cyclic Redundancy Code" for details.
    ///
    /// ```no_build,no_run
    /// Generator Polynomial: G(x) = x^16 + x^12 + x^5 + 1
    /// M(x) = (first bit) * x^n + (second bit) * x^n-1 + ... + (last bit) * x^0
    /// CRC[15..0] = Remainder[(M(x) * x^16) / G(x)]
    /// ```
    pub const fn calculate(buf: &[u8]) -> Self {
        let len = buf.len();

        let mut crc = 0u16;
        let mut i = 0;

        while i < len {
            crc = Self::crc_table(crc ^ ((buf[i] as u16) << 8));
            i = i.saturating_add(1);
        }

        Self(crc)
    }

    // Calculates the CRC-16 lookup value based on the `crc` value.
    #[inline(always)]
    const fn crc_table(mut crc: u16) -> u16 {
        let mut j = 0usize;

        while j < 8 {
            crc = (crc << 1) ^ Self::crc_rem(crc);
            j += 1;
        }

        crc
    }

    // Used to clear leading bit from CRC value.
    //
    // If the leading bit is set, adds the CRC-16 polynomial to correct the value.
    #[inline(always)]
    const fn crc_rem(crc: u16) -> u16 {
        if crc & 0x8000 != 0 { CRC16_POLY } else { 0 }
    }
}

impl Default for Crc16 {
    fn default() -> Self {
        Self::new()
    }
}

impl From<u16> for Crc16 {
    fn from(val: u16) -> Self {
        Self(val)
    }
}

impl From<Crc16> for u16 {
    fn from(val: Crc16) -> Self {
        val.bits()
    }
}

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

    #[test]
    fn test_crc16() {
        [0x7fa1]
            .map(Crc16::from)
            .into_iter()
            .zip([[0xff; 512]])
            .for_each(|(exp_crc, data)| {
                assert_eq!(Crc16::calculate(data.as_ref()), exp_crc);
            });
    }
}