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macro_rules! declare_varint {
($id:ident, $len:literal) => {
pub mod $id {
#[derive(Debug, Clone, Copy)]
pub struct Varint {
len: u8,
bytes: [u8; $len],
}
impl AsRef<[u8]> for Varint {
fn as_ref(&self) -> &[u8] {
&self.bytes[0..self.len as usize]
}
}
pub fn encode(mut v: $id) -> Varint {
let mut bytes = [0u8; $len];
let mut len = 0;
loop {
bytes[len as usize] = (v & 127) as u8 | 128;
v >>= 7;
len += 1;
if v == 0 {
break;
}
}
bytes[len as usize - 1] &= 127;
Varint { len, bytes }
}
pub fn decode(bytes: &[u8]) -> Option<$id> {
let mut v: $id = 0;
let mut bits = 0;
for b in bytes {
v = v.checked_add(((*b as $id) & 127) << bits)?;
bits += 7;
if *b < 128 {
if *b == 0 && bits > 7 {
return None;
}
if bytes.len() * 7 > bits {
return None;
}
break;
}
}
Some(v)
}
}
};
}
declare_varint!(u8, 2);
declare_varint!(u16, 3);
declare_varint!(u32, 5);
declare_varint!(u64, 10);
declare_varint!(u128, 19);
#[cfg(test)]
mod tests {
use quickcheck::TestResult;
use std::fmt::Debug;
use super::*;
fn should_equal<T: Debug + PartialEq>(left: T, right: T) -> TestResult {
if left == right {
TestResult::passed()
} else {
TestResult::error(format!("{:?} does not equal {:?}", left, right))
}
}
#[test]
fn test() {
assert_eq!(u32::encode(1234).as_ref(), &[210, 9]);
assert_eq!(u32::encode(128).as_ref(), &[128, 1]);
assert_eq!(u32::decode(&[128, 0]), None);
assert_eq!(u32::decode(&[128, 1, 0]), None);
}
quickcheck::quickcheck! {
fn size_u8(v: u8) -> TestResult {
let bits = 1.max(8 - v.leading_zeros() as usize);
let bytes = (bits + 6) / 7;
let res = u8::encode(v);
should_equal(res.as_ref().len(), bytes)
}
fn size_u16(v: u16) -> TestResult {
let bits = 1.max(16 - v.leading_zeros() as usize);
let bytes = (bits + 6) / 7;
let res = u16::encode(v);
should_equal(res.as_ref().len(), bytes)
}
fn size_u32(v: u32) -> TestResult {
let bits = 1.max(32 - v.leading_zeros() as usize);
let bytes = (bits + 6) / 7;
let res = u32::encode(v);
should_equal(res.as_ref().len(), bytes)
}
fn size_u64(v: u64) -> TestResult {
let bits = 1.max(64 - v.leading_zeros() as usize);
let bytes = (bits + 6) / 7;
let res = u64::encode(v);
should_equal(res.as_ref().len(), bytes)
}
fn size_u128(v: u128) -> TestResult {
let bits = 1.max(128 - v.leading_zeros() as usize);
let bytes = (bits + 6) / 7;
let res = u128::encode(v);
should_equal(res.as_ref().len(), bytes)
}
fn roundtrip_u8(v: u8) -> TestResult {
should_equal(u8::decode(u8::encode(v).as_ref()), Some(v))
}
fn roundtrip_u16(v: u16) -> TestResult {
should_equal(u16::decode(u16::encode(v).as_ref()), Some(v))
}
fn roundtrip_u32(v: u32) -> TestResult {
should_equal(u32::decode(u32::encode(v).as_ref()), Some(v))
}
fn roundtrip_u64(v: u64) -> TestResult {
should_equal(u64::decode(u64::encode(v).as_ref()), Some(v))
}
fn roundtrip_u128(v: u128) -> TestResult {
should_equal(u128::decode(u128::encode(v).as_ref()), Some(v))
}
}
}
