Mercurial > touhou
view src/util/bitstream.rs @ 744:3687205fe620
anm0_vm: Use the unused u16 to store the anm layer to use.
author | Emmanuel Gil Peyrot <linkmauve@linkmauve.fr> |
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date | Sat, 18 Jan 2020 16:25:45 +0100 (2020-01-18) |
parents | afa012bb8021 |
children |
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//! Bitstream module. use std::io; /// Wrapper around any `Read` trait, to allow bit operations. pub struct BitStream<R: io::Read + io::Seek> { io: R, remaining_bits: usize, byte: u8, } impl<R: io::Read + io::Seek> BitStream<R> { /// Create a new bitstream. pub fn new(io: R) -> BitStream<R> { BitStream { io, remaining_bits: 0, byte: 0, } } /// Seek inside the bitstream, ditching any unused data read. pub fn seek(&mut self, seek_from: io::SeekFrom) -> io::Result<u64> { self.remaining_bits = 0; self.byte = 0; self.io.seek(seek_from) } fn fill_byte(&mut self) -> io::Result<()> { assert!(self.remaining_bits == 0); let mut buf = [0u8; 1]; self.io.read_exact(&mut buf)?; self.byte = buf[0]; self.remaining_bits = 8; Ok(()) } /// Read only one bit from the stream. pub fn read_bit(&mut self) -> io::Result<bool> { if self.remaining_bits == 0 { self.fill_byte()?; } self.remaining_bits -= 1; Ok((self.byte >> self.remaining_bits) & 0x01 != 0) } /// Read `nb_bits` bits from the stream. pub fn read(&mut self, nb_bits: usize) -> io::Result<usize> { let mut nb_bits2 = nb_bits; let mut value: usize = 0; while nb_bits2 > 0 { if self.remaining_bits == 0 { self.fill_byte()?; } let read = if nb_bits2 > self.remaining_bits { self.remaining_bits } else { nb_bits2 }; nb_bits2 -= read; self.remaining_bits -= read; value |= (self.byte as usize >> self.remaining_bits) << nb_bits2; } Ok(value & ((1 << nb_bits) - 1)) } /// Read a given amount of bytes. pub fn read_bytes(&mut self, nb_bytes: usize) -> io::Result<Vec<u8>> { let mut buf = vec![0u8; nb_bytes]; self.io.read_exact(&mut buf)?; Ok(buf) } } #[cfg(test)] mod tests { use super::*; use crate::util::SeekableSlice; #[test] fn bit_by_bit() { let data = SeekableSlice::new(&[1, 2, 3]); let mut bitstream = BitStream::new(data); // 1 assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), true); // 2 assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), true); assert_eq!(bitstream.read_bit().unwrap(), false); // 3 assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read_bit().unwrap(), true); assert_eq!(bitstream.read_bit().unwrap(), true); // Can’t read after the end. bitstream.read_bit().unwrap_err(); } #[test] fn byte_by_byte() { let data = SeekableSlice::new(&[1, 2, 3]); let mut bitstream = BitStream::new(data); assert_eq!(bitstream.read(8).unwrap(), 1); assert_eq!(bitstream.read(8).unwrap(), 2); assert_eq!(bitstream.read(8).unwrap(), 3); // Can’t read after the end. bitstream.read(1).unwrap_err(); } #[test] fn unaligned_bytes() { let data = SeekableSlice::new(&[0, 129, 1, 128]); let mut bitstream = BitStream::new(data); assert_eq!(bitstream.read_bit().unwrap(), false); assert_eq!(bitstream.read(8).unwrap(), 1); assert_eq!(bitstream.read(8).unwrap(), 2); assert_eq!(bitstream.read(8).unwrap(), 3); assert_eq!(bitstream.read(7).unwrap(), 0); // Can’t read after the end. bitstream.read(1).unwrap_err(); } }