obkv 0.3.0

Optimized-bytes key and a value store
Documentation 
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fn varint_length_packed(data: &[u8]) -> Option<u32> {
    let mut i = 0;
    for _ in 0..data.len() {
        if (*data.get(i)? & 0x80) == 0 {
            break;
        }
        i += 1;
    }
    if i == data.len() {
        Some(0)
    } else {
        Some(i as u32 + 1)
    }
}

#[must_use]
pub fn varint_encode32(bytes: &mut [u8], value: u32) -> &[u8] {
    let b = 128;

    if value < (1 << 7) {
        bytes[0] = value as u8;
        &bytes[..1]
    } else if value < (1 << 14) {
        bytes[0] = (value | b) as u8;
        bytes[1] = (value >> 7) as u8;
        &bytes[..2]
    } else if value < (1 << 21) {
        bytes[0] = (value | b) as u8;
        bytes[1] = ((value >> 7) | b) as u8;
        bytes[2] = (value >> 14) as u8;
        &bytes[..3]
    } else if value < (1 << 28) {
        bytes[0] = (value | b) as u8;
        bytes[1] = ((value >> 7) | b) as u8;
        bytes[2] = ((value >> 14) | b) as u8;
        bytes[3] = (value >> 21) as u8;
        &bytes[..4]
    } else {
        bytes[0] = (value | b) as u8;
        bytes[1] = ((value >> 7) | b) as u8;
        bytes[2] = ((value >> 14) | b) as u8;
        bytes[3] = ((value >> 21) | b) as u8;
        bytes[4] = (value >> 28) as u8;
        &bytes[..5]
    }
}

pub fn varint_decode32(data: &[u8], value: &mut u32) -> Option<usize> {
    let len = varint_length_packed(data.get(..data.len().min(5))?)?;
    let mut val = (*data.first()? & 0x7f) as u32;
    if len > 1 {
        val |= ((*data.get(1)? & 0x7f) as u32) << 7;
        if len > 2 {
            val |= ((*data.get(2)? & 0x7f) as u32) << 14;
            if len > 3 {
                val |= ((*data.get(3)? & 0x7f) as u32) << 21;
                if len > 4 {
                    val |= (*data.get(4)? as u32) << 28;
                }
            }
        }
    }
    *value = val;
    Some(len as usize)
}

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

    quickcheck! {
        fn qc_codec_u32(num: u32) -> bool {
            let mut buf = [0; 10];
            let mut val = 0;
            let buf = varint_encode32(&mut buf, num);
            varint_decode32(buf, &mut val).unwrap();

            num == val
        }
    }
}