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#[inline]
pub fn write_to_vec(vec: &mut Vec<u8>, byte: u8) {
vec.push(byte);
}
#[cfg(target_pointer_width = "32")]
const USIZE_LEB128_SIZE: usize = 5;
#[cfg(target_pointer_width = "64")]
const USIZE_LEB128_SIZE: usize = 10;
macro_rules! leb128_size {
(u16) => (3);
(u32) => (5);
(u64) => (10);
(u128) => (19);
(usize) => (USIZE_LEB128_SIZE);
}
macro_rules! impl_write_unsigned_leb128 {
($fn_name:ident, $int_ty:ident) => (
#[inline]
pub fn $fn_name(out: &mut Vec<u8>, mut value: $int_ty) {
for _ in 0 .. leb128_size!($int_ty) {
let mut byte = (value & 0x7F) as u8;
value >>= 7;
if value != 0 {
byte |= 0x80;
}
write_to_vec(out, byte);
if value == 0 {
break;
}
}
}
)
}
impl_write_unsigned_leb128!(write_u16_leb128, u16);
impl_write_unsigned_leb128!(write_u32_leb128, u32);
impl_write_unsigned_leb128!(write_u64_leb128, u64);
impl_write_unsigned_leb128!(write_u128_leb128, u128);
impl_write_unsigned_leb128!(write_usize_leb128, usize);
macro_rules! impl_read_unsigned_leb128 {
($fn_name:ident, $int_ty:ident) => (
#[inline]
pub fn $fn_name(slice: &[u8]) -> ($int_ty, usize) {
let mut result: $int_ty = 0;
let mut shift = 0;
let mut position = 0;
for _ in 0 .. leb128_size!($int_ty) {
let byte = unsafe {
*slice.get_unchecked(position)
};
position += 1;
result |= ((byte & 0x7F) as $int_ty) << shift;
if (byte & 0x80) == 0 {
break;
}
shift += 7;
}
assert!(position <= slice.len());
(result, position)
}
)
}
impl_read_unsigned_leb128!(read_u16_leb128, u16);
impl_read_unsigned_leb128!(read_u32_leb128, u32);
impl_read_unsigned_leb128!(read_u64_leb128, u64);
impl_read_unsigned_leb128!(read_u128_leb128, u128);
impl_read_unsigned_leb128!(read_usize_leb128, usize);
#[inline]
pub fn write_signed_leb128_to<W>(mut value: i128, mut write: W)
where W: FnMut(u8)
{
loop {
let mut byte = (value as u8) & 0x7f;
value >>= 7;
let more = !((((value == 0) && ((byte & 0x40) == 0)) ||
((value == -1) && ((byte & 0x40) != 0))));
if more {
byte |= 0x80;
}
write(byte);
if !more {
break;
}
}
}
pub fn write_signed_leb128(out: &mut Vec<u8>, value: i128) {
write_signed_leb128_to(value, |v| write_to_vec(out, v))
}
#[inline]
pub fn read_signed_leb128(data: &[u8], start_position: usize) -> (i128, usize) {
let mut result = 0;
let mut shift = 0;
let mut position = start_position;
let mut byte;
loop {
byte = data[position];
position += 1;
result |= ((byte & 0x7F) as i128) << shift;
shift += 7;
if (byte & 0x80) == 0 {
break;
}
}
if (shift < 64) && ((byte & 0x40) != 0) {
result |= -(1 << shift);
}
(result, position - start_position)
}
macro_rules! impl_test_unsigned_leb128 {
($test_name:ident, $write_fn_name:ident, $read_fn_name:ident, $int_ty:ident) => (
#[test]
fn $test_name() {
let mut stream = Vec::new();
for x in 0..62 {
$write_fn_name(&mut stream, (3u64 << x) as $int_ty);
}
let mut position = 0;
for x in 0..62 {
let expected = (3u64 << x) as $int_ty;
let (actual, bytes_read) = $read_fn_name(&stream[position ..]);
assert_eq!(expected, actual);
position += bytes_read;
}
assert_eq!(stream.len(), position);
}
)
}
impl_test_unsigned_leb128!(test_u16_leb128, write_u16_leb128, read_u16_leb128, u16);
impl_test_unsigned_leb128!(test_u32_leb128, write_u32_leb128, read_u32_leb128, u32);
impl_test_unsigned_leb128!(test_u64_leb128, write_u64_leb128, read_u64_leb128, u64);
impl_test_unsigned_leb128!(test_u128_leb128, write_u128_leb128, read_u128_leb128, u128);
impl_test_unsigned_leb128!(test_usize_leb128, write_usize_leb128, read_usize_leb128, usize);
#[test]
fn test_signed_leb128() {
let values: Vec<_> = (-500..500).map(|i| i * 0x12345789ABCDEF).collect();
let mut stream = Vec::new();
for &x in &values {
write_signed_leb128(&mut stream, x);
}
let mut pos = 0;
for &x in &values {
let (value, bytes_read) = read_signed_leb128(&mut stream, pos);
pos += bytes_read;
assert_eq!(x, value);
}
assert_eq!(pos, stream.len());
}