vendor/gimli-0.26.1/src/leb128.rs - toolchain/rustc - Git at Google

 //! 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);
         }
     }
 }
	//! 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);
	}
	}
	}