bitutils2 0.1.5

A package of tools for bit manipulations, including bit indexing, bitfields, and a variation of regular expressions for binary data
Documentation 
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// https://doc.rust-lang.org/src/core/num/dec2flt/common.rs.html

/// Helper methods to process immutable bytes.
pub(crate) trait ByteSlice {
    /// Reads 8 bytes as a 64-bit integer in little-endian order.
    fn read_u64(&self) -> u64;

    /// Writes a 64-bit integer as 8 bytes in little-endian order.
    fn write_u64(&mut self, value: u64);

    /// Calculate the offset of a slice from another.
    fn offset_from(&self, other: &Self) -> isize;

    /// Iteratively parse and consume digits from bytes.
    /// Returns the same bytes with consumed digits being
    /// elided.
    fn parse_digits(&self, func: impl FnMut(u8)) -> &Self;
}

impl ByteSlice for [u8] {
    #[inline(always)] // inlining this is crucial to remove bound checks
    fn read_u64(&self) -> u64 {
        let mut tmp = [0; 8];
        tmp.copy_from_slice(&self[..8]);
        u64::from_le_bytes(tmp)
    }

    #[inline(always)] // inlining this is crucial to remove bound checks
    fn write_u64(&mut self, value: u64) {
        self[..8].copy_from_slice(&value.to_le_bytes())
    }

    #[inline]
    fn offset_from(&self, other: &Self) -> isize {
        other.len() as isize - self.len() as isize
    }

    #[inline]
    fn parse_digits(&self, mut func: impl FnMut(u8)) -> &Self {
        let mut s = self;

        while let Some((c, s_next)) = s.split_first() {
            let c = c.wrapping_sub(b'0');
            if c < 10 {
                func(c);
                s = s_next;
            } else {
                break;
            }
        }

        s
    }
}

/// Determine if 8 bytes are all decimal digits.
/// This does not care about the order in which the bytes were loaded.
pub(crate) fn is_8digits(v: u64) -> bool {
    let a = v.wrapping_add(0x4646_4646_4646_4646);
    let b = v.wrapping_sub(0x3030_3030_3030_3030);
    (a | b) & 0x8080_8080_8080_8080 == 0
}