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//! Read and write DWARF's "Little Endian Base 128" (LEB128) variable length
//! integer encoding.
//!
//! The implementation is a direct translation of the psuedocode in the DWARF 4
//! standard's appendix C.
//!
//! Read and write signed integers:
//!
//! ```
//! # #[cfg(all(feature = "read", feature = "write"))] {
//! use gimli::{EndianSlice, NativeEndian, leb128};
//!
//! let mut buf = [0; 1024];
//!
//! // Write to anything that implements `std::io::Write`.
//! {
//! let mut writable = &mut buf[..];
//! leb128::write::signed(&mut writable, -12345).expect("Should write number");
//! }
//!
//! // Read from anything that implements `gimli::Reader`.
//! let mut readable = EndianSlice::new(&buf[..], NativeEndian);
//! let val = leb128::read::signed(&mut readable).expect("Should read number");
//! assert_eq!(val, -12345);
//! # }
//! ```
//!
//! Or read and write unsigned integers:
//!
//! ```
//! # #[cfg(all(feature = "read", feature = "write"))] {
//! use gimli::{EndianSlice, NativeEndian, leb128};
//!
//! let mut buf = [0; 1024];
//!
//! {
//! let mut writable = &mut buf[..];
//! leb128::write::unsigned(&mut writable, 98765).expect("Should write number");
//! }
//!
//! let mut readable = EndianSlice::new(&buf[..], NativeEndian);
//! let val = leb128::read::unsigned(&mut readable).expect("Should read number");
//! assert_eq!(val, 98765);
//! # }
//! ```
const CONTINUATION_BIT: u8 = 1 << 7;
#[cfg(feature = "read-core")]
const SIGN_BIT: u8 = 1 << 6;
#[inline]
fn low_bits_of_byte(byte: u8) -> u8 {
byte & !CONTINUATION_BIT
}
#[inline]
#[allow(dead_code)]
fn low_bits_of_u64(val: u64) -> u8 {
let byte = val & u64::from(core::u8::MAX);
low_bits_of_byte(byte as u8)
}
/// A module for reading signed and unsigned integers that have been LEB128
/// encoded.
#[cfg(feature = "read-core")]
pub mod read {
use super::{low_bits_of_byte, CONTINUATION_BIT, SIGN_BIT};
use crate::read::{Error, Reader, Result};
/// Read bytes until the LEB128 continuation bit is not set.
pub fn skip<R: Reader>(r: &mut R) -> Result<()> {
loop {
let byte = r.read_u8()?;
if byte & CONTINUATION_BIT == 0 {
return Ok(());
}
}
}
/// Read an unsigned LEB128 number from the given `Reader` and
/// return it or an error if reading failed.
pub fn unsigned<R: Reader>(r: &mut R) -> Result<u64> {
let mut result = 0;
let mut shift = 0;
loop {
let byte = r.read_u8()?;
if shift == 63 && byte != 0x00 && byte != 0x01 {
return Err(Error::BadUnsignedLeb128);
}
let low_bits = u64::from(low_bits_of_byte(byte));
result |= low_bits << shift;
if byte & CONTINUATION_BIT == 0 {
return Ok(result);
}
shift += 7;
}
}
/// Read an LEB128 u16 from the given `Reader` and
/// return it or an error if reading failed.
pub fn u16<R: Reader>(r: &mut R) -> Result<u16> {
let byte = r.read_u8()?;
let mut result = u16::from(low_bits_of_byte(byte));
if byte & CONTINUATION_BIT == 0 {
return Ok(result);
}
let byte = r.read_u8()?;
result |= u16::from(low_bits_of_byte(byte)) << 7;
if byte & CONTINUATION_BIT == 0 {
return Ok(result);
}
let byte = r.read_u8()?;
if byte > 0x03 {
return Err(Error::BadUnsignedLeb128);
}
result += u16::from(byte) << 14;
Ok(result)
}
/// Read a signed LEB128 number from the given `Reader` and
/// return it or an error if reading failed.
pub fn signed<R: Reader>(r: &mut R) -> Result<i64> {
let mut result = 0;
let mut shift = 0;
let size = 64;
let mut byte;
loop {
byte = r.read_u8()?;
if shift == 63 && byte != 0x00 && byte != 0x7f {
return Err(Error::BadSignedLeb128);
}
let low_bits = i64::from(low_bits_of_byte(byte));
result |= low_bits << shift;
shift += 7;
if byte & CONTINUATION_BIT == 0 {
break;
}
}
if shift < size && (SIGN_BIT & byte) == SIGN_BIT {
// Sign extend the result.
result |= !0 << shift;
}
Ok(result)
}
}
/// A module for writing integers encoded as LEB128.
#[cfg(feature = "write")]
pub mod write {
use super::{low_bits_of_u64, CONTINUATION_BIT};
use std::io;
/// Write the given unsigned number using the LEB128 encoding to the given
/// `std::io::Write`able. Returns the number of bytes written to `w`, or an
/// error if writing failed.
pub fn unsigned<W>(w: &mut W, mut val: u64) -> Result<usize, io::Error>
where
W: io::Write,
{
let mut bytes_written = 0;
loop {
let mut byte = low_bits_of_u64(val);
val >>= 7;
if val != 0 {
// More bytes to come, so set the continuation bit.
byte |= CONTINUATION_BIT;
}
let buf = [byte];
w.write_all(&buf)?;
bytes_written += 1;
if val == 0 {
return Ok(bytes_written);
}
}
}
/// Return the size of the LEB128 encoding of the given unsigned number.
pub fn uleb128_size(mut val: u64) -> usize {
let mut size = 0;
loop {
val >>= 7;
size += 1;
if val == 0 {
return size;
}
}
}
/// Write the given signed number using the LEB128 encoding to the given
/// `std::io::Write`able. Returns the number of bytes written to `w`, or an
/// error if writing failed.
pub fn signed<W>(w: &mut W, mut val: i64) -> Result<usize, io::Error>
where
W: io::Write,
{
let mut bytes_written = 0;
loop {
let mut byte = val as u8;
// Keep the sign bit for testing
val >>= 6;
let done = val == 0 || val == -1;
if done {
byte &= !CONTINUATION_BIT;
} else {
// Remove the sign bit
val >>= 1;
// More bytes to come, so set the continuation bit.
byte |= CONTINUATION_BIT;
}
let buf = [byte];
w.write_all(&buf)?;
bytes_written += 1;
if done {
return Ok(bytes_written);
}
}
}
/// Return the size of the LEB128 encoding of the given signed number.
pub fn sleb128_size(mut val: i64) -> usize {
let mut size = 0;
loop {
val >>= 6;
let done = val == 0 || val == -1;
val >>= 1;
size += 1;
if done {
return size;
}
}
}
}
#[cfg(test)]
#[cfg(all(feature = "read", feature = "write"))]
mod tests {
use super::{low_bits_of_byte, low_bits_of_u64, read, write, CONTINUATION_BIT};
use crate::endianity::NativeEndian;
use crate::read::{EndianSlice, Error, ReaderOffsetId};
trait ResultExt {
fn map_eof(self, input: &[u8]) -> Self;
}
impl<T> ResultExt for Result<T, Error> {
fn map_eof(self, input: &[u8]) -> Self {
match self {
Err(Error::UnexpectedEof(id)) => {
let id = ReaderOffsetId(id.0 - input.as_ptr() as u64);
Err(Error::UnexpectedEof(id))
}
r => r,
}
}
}
#[test]
fn test_low_bits_of_byte() {
for i in 0..127 {
assert_eq!(i, low_bits_of_byte(i));
assert_eq!(i, low_bits_of_byte(i | CONTINUATION_BIT));
}
}
#[test]
fn test_low_bits_of_u64() {
for i in 0u64..127 {
assert_eq!(i as u8, low_bits_of_u64(1 << 16 | i));
assert_eq!(
i as u8,
low_bits_of_u64(i << 16 | i | (u64::from(CONTINUATION_BIT)))
);
}
}
// Examples from the DWARF 4 standard, section 7.6, figure 22.
#[test]
fn test_read_unsigned() {
let buf = [2u8];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
2,
read::unsigned(&mut readable).expect("Should read number")
);
let buf = [127u8];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
127,
read::unsigned(&mut readable).expect("Should read number")
);
let buf = [CONTINUATION_BIT, 1];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
128,
read::unsigned(&mut readable).expect("Should read number")
);
let buf = [1u8 | CONTINUATION_BIT, 1];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
129,
read::unsigned(&mut readable).expect("Should read number")
);
let buf = [2u8 | CONTINUATION_BIT, 1];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
130,
read::unsigned(&mut readable).expect("Should read number")
);
let buf = [57u8 | CONTINUATION_BIT, 100];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
12857,
read::unsigned(&mut readable).expect("Should read number")
);
}
// Examples from the DWARF 4 standard, section 7.6, figure 23.
#[test]
fn test_read_signed() {
let buf = [2u8];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(2, read::signed(&mut readable).expect("Should read number"));
let buf = [0x7eu8];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(-2, read::signed(&mut readable).expect("Should read number"));
let buf = [127u8 | CONTINUATION_BIT, 0];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
127,
read::signed(&mut readable).expect("Should read number")
);
let buf = [1u8 | CONTINUATION_BIT, 0x7f];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
-127,
read::signed(&mut readable).expect("Should read number")
);
let buf = [CONTINUATION_BIT, 1];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
128,
read::signed(&mut readable).expect("Should read number")
);
let buf = [CONTINUATION_BIT, 0x7f];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
-128,
read::signed(&mut readable).expect("Should read number")
);
let buf = [1u8 | CONTINUATION_BIT, 1];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
129,
read::signed(&mut readable).expect("Should read number")
);
let buf = [0x7fu8 | CONTINUATION_BIT, 0x7e];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
-129,
read::signed(&mut readable).expect("Should read number")
);
}
#[test]
fn test_read_signed_63_bits() {
let buf = [
CONTINUATION_BIT,
CONTINUATION_BIT,
CONTINUATION_BIT,
CONTINUATION_BIT,
CONTINUATION_BIT,
CONTINUATION_BIT,
CONTINUATION_BIT,
CONTINUATION_BIT,
0x40,
];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
-0x4000_0000_0000_0000,
read::signed(&mut readable).expect("Should read number")
);
}
#[test]
fn test_read_unsigned_not_enough_data() {
let buf = [CONTINUATION_BIT];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
read::unsigned(&mut readable).map_eof(&buf),
Err(Error::UnexpectedEof(ReaderOffsetId(1)))
);
}
#[test]
fn test_read_signed_not_enough_data() {
let buf = [CONTINUATION_BIT];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
read::signed(&mut readable).map_eof(&buf),
Err(Error::UnexpectedEof(ReaderOffsetId(1)))
);
}
#[test]
fn test_write_unsigned_not_enough_space() {
let mut buf = [0; 1];
let mut writable = &mut buf[..];
match write::unsigned(&mut writable, 128) {
Err(e) => assert_eq!(e.kind(), std::io::ErrorKind::WriteZero),
otherwise => panic!("Unexpected: {:?}", otherwise),
}
}
#[test]
fn test_write_signed_not_enough_space() {
let mut buf = [0; 1];
let mut writable = &mut buf[..];
match write::signed(&mut writable, 128) {
Err(e) => assert_eq!(e.kind(), std::io::ErrorKind::WriteZero),
otherwise => panic!("Unexpected: {:?}", otherwise),
}
}
#[test]
fn dogfood_signed() {
fn inner(i: i64) {
let mut buf = [0u8; 1024];
{
let mut writable = &mut buf[..];
write::signed(&mut writable, i).expect("Should write signed number");
}
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
let result = read::signed(&mut readable).expect("Should be able to read it back again");
assert_eq!(i, result);
}
for i in -513..513 {
inner(i);
}
inner(core::i64::MIN);
}
#[test]
fn dogfood_unsigned() {
for i in 0..1025 {
let mut buf = [0u8; 1024];
{
let mut writable = &mut buf[..];
write::unsigned(&mut writable, i).expect("Should write signed number");
}
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
let result =
read::unsigned(&mut readable).expect("Should be able to read it back again");
assert_eq!(i, result);
}
}
#[test]
fn test_read_unsigned_overflow() {
let buf = [
2u8 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
1,
];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert!(read::unsigned(&mut readable).is_err());
}
#[test]
fn test_read_signed_overflow() {
let buf = [
2u8 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
2 | CONTINUATION_BIT,
1,
];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert!(read::signed(&mut readable).is_err());
}
#[test]
fn test_read_multiple() {
let buf = [2u8 | CONTINUATION_BIT, 1u8, 1u8];
let mut readable = EndianSlice::new(&buf[..], NativeEndian);
assert_eq!(
read::unsigned(&mut readable).expect("Should read first number"),
130u64
);
assert_eq!(
read::unsigned(&mut readable).expect("Should read first number"),
1u64
);
}
#[test]
fn test_read_u16() {
for (buf, val) in [
(&[2][..], 2),
(&[0x7f][..], 0x7f),
(&[0x80, 1][..], 0x80),
(&[0x81, 1][..], 0x81),
(&[0x82, 1][..], 0x82),
(&[0xff, 0x7f][..], 0x3fff),
(&[0x80, 0x80, 1][..], 0x4000),
(&[0xff, 0xff, 1][..], 0x7fff),
(&[0xff, 0xff, 3][..], 0xffff),
]
.iter()
{
let mut readable = EndianSlice::new(buf, NativeEndian);
assert_eq!(*val, read::u16(&mut readable).expect("Should read number"));
}
for buf in [
&[0x80][..],
&[0x80, 0x80][..],
&[0x80, 0x80, 4][..],
&[0x80, 0x80, 0x80, 3][..],
]
.iter()
{
let mut readable = EndianSlice::new(buf, NativeEndian);
assert!(read::u16(&mut readable).is_err(), "{:?}", buf);
}
}
}