2 pub fn write_to_vec(vec: &mut Vec<u8>, byte: u8) {
6 #[cfg(target_pointer_width = "32")]
7 const USIZE_LEB128_SIZE: usize = 5;
8 #[cfg(target_pointer_width = "64")]
9 const USIZE_LEB128_SIZE: usize = 10;
11 macro_rules! leb128_size {
29 macro_rules! impl_write_unsigned_leb128 {
30 ($fn_name:ident, $int_ty:ident) => {
32 pub fn $fn_name(out: &mut Vec<u8>, mut value: $int_ty) {
33 for _ in 0..leb128_size!($int_ty) {
34 let mut byte = (value & 0x7F) as u8;
40 write_to_vec(out, byte);
50 impl_write_unsigned_leb128!(write_u16_leb128, u16);
51 impl_write_unsigned_leb128!(write_u32_leb128, u32);
52 impl_write_unsigned_leb128!(write_u64_leb128, u64);
53 impl_write_unsigned_leb128!(write_u128_leb128, u128);
54 impl_write_unsigned_leb128!(write_usize_leb128, usize);
56 macro_rules! impl_read_unsigned_leb128 {
57 ($fn_name:ident, $int_ty:ident) => {
59 pub fn $fn_name(slice: &[u8]) -> ($int_ty, usize) {
60 let mut result: $int_ty = 0;
64 for _ in 0..leb128_size!($int_ty) {
65 let byte = unsafe { *slice.get_unchecked(position) };
67 result |= ((byte & 0x7F) as $int_ty) << shift;
68 if (byte & 0x80) == 0 {
74 // Do a single bounds check at the end instead of for every byte.
75 assert!(position <= slice.len());
82 impl_read_unsigned_leb128!(read_u16_leb128, u16);
83 impl_read_unsigned_leb128!(read_u32_leb128, u32);
84 impl_read_unsigned_leb128!(read_u64_leb128, u64);
85 impl_read_unsigned_leb128!(read_u128_leb128, u128);
86 impl_read_unsigned_leb128!(read_usize_leb128, usize);
89 /// encodes an integer using signed leb128 encoding and stores
90 /// the result using a callback function.
92 /// The callback `write` is called once for each position
93 /// that is to be written to with the byte to be encoded
95 pub fn write_signed_leb128_to<W>(mut value: i128, mut write: W)
100 let mut byte = (value as u8) & 0x7f;
103 !(((value == 0) && ((byte & 0x40) == 0)) || ((value == -1) && ((byte & 0x40) != 0)));
106 byte |= 0x80; // Mark this byte to show that more bytes will follow.
118 pub fn write_signed_leb128(out: &mut Vec<u8>, value: i128) {
119 write_signed_leb128_to(value, |v| write_to_vec(out, v))
123 pub fn read_signed_leb128(data: &[u8], start_position: usize) -> (i128, usize) {
126 let mut position = start_position;
130 byte = data[position];
132 result |= i128::from(byte & 0x7F) << shift;
135 if (byte & 0x80) == 0 {
140 if (shift < 64) && ((byte & 0x40) != 0) {
142 result |= -(1 << shift);
145 (result, position - start_position)