| #[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; |
| } |
| |
| // Do a single bounds check at the end instead of for every byte. |
| 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] |
| /// encodes an integer using signed leb128 encoding and stores |
| /// the result using a callback function. |
| /// |
| /// The callback `write` is called once for each position |
| /// that is to be written to with the byte to be encoded |
| /// at that position. |
| 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; // Mark this byte to show that more bytes will follow. |
| } |
| |
| write(byte); |
| |
| if !more { |
| break; |
| } |
| } |
| } |
| |
| #[inline] |
| 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 |= i128::from(byte & 0x7F) << shift; |
| shift += 7; |
| |
| if (byte & 0x80) == 0 { |
| break; |
| } |
| } |
| |
| if (shift < 64) && ((byte & 0x40) != 0) { |
| // sign extend |
| result |= -(1 << shift); |
| } |
| |
| (result, position - start_position) |
| } |