path: root/users/edef/refscan/src/lib.rs

use self::simd::u8x32;

fn prefilter(haystack: u8x32) -> u32 {
    let alp = haystack.gt(u8x32::splat(b'a' - 1)) & haystack.lt(u8x32::splat(b'z' + 1));
    let num = haystack.gt(u8x32::splat(b'0' - 1)) & haystack.lt(u8x32::splat(b'9' + 1));
    alp | num
}

/// scan_clean returns `Err(&buffer[..n])` of known pointer-free data,
/// or `Ok(buffer)` if the entire buffer is pointer-free.
pub fn scan_clean(buffer: &[u8]) -> Result<&[u8], &[u8]> {
    let buffer = {
        let n = buffer.len() & !31;
        &buffer[..n]
    };

    let mut masks = buffer
        .chunks_exact(32)
        .map(|chunk| prefilter(u8x32::from_slice_unaligned(chunk)))
        .enumerate()
        .map(|e| (e.0 * 32, e.1))
        .peekable();

    while let Some((offset, mask)) = masks.next() {
        let peek = masks.peek().map(|x| x.1).unwrap_or(!0 >> 1);
        let n = (!mask).leading_zeros() + (!peek).trailing_zeros();
        if n >= 32 {
            let offset = offset + mask.trailing_zeros() as usize;
            return Err(&buffer[..offset]);
        }
    }

    Ok(buffer)
}

#[cfg(test)]
mod test {
    #[test]
    fn scan_tail() {
        let buffer = b"_xfbmj7sl2ikicym9x3yq7cms5qx1w39k";
        assert_eq!(crate::scan_clean(buffer), Err(&buffer[..1]));
    }
    #[test]
    fn scan_straddle() {
        let buffer = b"________________xfbmj7sl2ikicym9x3yq7cms5qx1w39k________________";
        assert_eq!(crate::scan_clean(buffer), Err(&buffer[..16]));
    }
    #[test]
    fn scan_clean() {
        let buffer = b"x_______________xfbmj7sl2ikicym9x3yq-cms5qx1w3-k________________";
        assert_eq!(crate::scan_clean(buffer), Ok(&buffer[..]));
    }
}

mod simd {
    #[cfg(target_arch = "x86")]
    use std::arch::x86 as arch;
    #[cfg(target_arch = "x86_64")]
    use std::arch::x86_64 as arch;
    use {
        arch::{__m256i, _mm256_cmpgt_epi8, _mm256_movemask_epi8, _mm256_set1_epi8},
        std::ptr,
    };

    #[derive(Copy, Clone)]
    pub struct u8x32(__m256i);

    impl u8x32 {
        #[inline(always)]
        pub fn from_slice_unaligned(slice: &[u8]) -> Self {
            assert_eq!(slice.len(), 32);
            u8x32(unsafe { ptr::read_unaligned(slice.as_ptr().cast()) })
        }

        #[inline(always)]
        pub fn splat(x: u8) -> Self {
            u8x32(unsafe { _mm256_set1_epi8(x as i8) })
        }

        #[inline(always)]
        pub fn gt(self, b: Self) -> u32 {
            unsafe { _mm256_movemask_epi8(_mm256_cmpgt_epi8(self.0, b.0)) as u32 }
        }

        #[inline(always)]
        pub fn lt(self, b: Self) -> u32 {
            b.gt(self)
        }
    }
}