2 pub enum BitReaderMode {
10 pub enum BitReaderError {
16 use self::BitReaderError::*;
18 pub type BitReaderResult<T> = Result<T, BitReaderError>;
21 pub struct BitReader<'a> {
30 impl<'a> BitReader<'a> {
32 pub fn new(src: &'a [u8], size: usize, mode: BitReaderMode) -> Self {
33 if src.len() < size { panic!("size is less than needed"); }
34 BitReader{ cache: 0, pos: 0, bits: 0, end: size, src: src, mode: mode }
37 pub fn tell(&self) -> usize {
38 self.pos * 8 - (self.bits as usize)
41 pub fn left(&self) -> isize {
42 ((self.end as isize) - (self.pos as isize)) * 8 + (self.bits as isize)
45 fn fill32be(&mut self, src: &[u8]) {
46 let nw = (((src[0] as u32) << 24) |
47 ((src[1] as u32) << 16) |
48 ((src[2] as u32) << 8) |
49 ((src[3] as u32) << 0)) as u64;
50 self.cache |= nw << (32 - self.bits);
53 fn fill32le16(&mut self, src: &[u8], realbits: u8) {
54 let mut nw = (((src[1] as u32) << 24) |
55 ((src[0] as u32) << 16) |
56 ((src[3] as u32) << 8) |
57 ((src[2] as u32) << 0)) as u64;
58 if realbits <= 16 { nw >>= 16; }
59 self.cache |= nw << self.bits;
62 fn fill32le32(&mut self, src: &[u8]) {
63 let nw = (((src[3] as u32) << 24) |
64 ((src[2] as u32) << 16) |
65 ((src[1] as u32) << 8) |
66 ((src[0] as u32) << 0)) as u64;
67 self.cache |= nw << self.bits;
70 fn refill(&mut self) -> BitReaderResult<()> {
71 if self.pos >= self.end { return Err(BitstreamEnd) }
72 while self.bits <= 32 {
73 if self.pos + 4 <= self.end {
74 let buf = &self.src[self.pos..];
76 BitReaderMode::BE => self.fill32be (buf),
77 BitReaderMode::LE16MSB => self.fill32le16(buf, 32),
78 BitReaderMode::LE => self.fill32le32(buf),
79 BitReaderMode::LE32MSB => self.fill32le32(buf),
84 let mut buf: [u8; 4] = [0, 0, 0, 0];
85 let mut newbits: u8 = 0;
87 if self.pos < self.end {
88 buf[i] = self.src[self.pos];
89 self.pos = self.pos + 1;
93 if newbits == 0 { break; }
95 BitReaderMode::BE => self.fill32be (&buf),
96 BitReaderMode::LE16MSB => self.fill32le16(&buf, newbits),
97 BitReaderMode::LE => self.fill32le32(&buf),
98 BitReaderMode::LE32MSB => self.fill32le32(&buf),
100 self.bits += newbits;
106 fn read_cache(&mut self, nbits: u8) -> u32 {
107 let res = match self.mode {
108 BitReaderMode::LE => ((1u64 << nbits) - 1) & self.cache,
109 _ => (self.cache as u64) >> (64 - nbits),
114 fn read_cache_s(&mut self, nbits: u8) -> i32 {
115 let res = match self.mode {
116 BitReaderMode::LE => ((self.cache as i64) << (64 - nbits)) >> (64 - nbits),
117 _ => (self.cache as i64) >> (64 - nbits),
122 fn skip_cache(&mut self, nbits: u8) {
124 BitReaderMode::LE => self.cache >>= nbits,
125 _ => self.cache <<= nbits,
130 fn reset_cache(&mut self) {
135 pub fn read(&mut self, nbits: u8) -> BitReaderResult<u32> {
136 if nbits == 0 { return Ok(0) }
137 if nbits > 32 { return Err(TooManyBitsRequested) }
138 if self.bits < nbits {
139 if let Err(err) = self.refill() { return Err(err) }
140 if self.bits < nbits { return Err(BitstreamEnd) }
142 let res = self.read_cache(nbits);
143 self.skip_cache(nbits);
147 pub fn read_s(&mut self, nbits: u8) -> BitReaderResult<i32> {
148 if nbits == 0 || nbits > 32 { return Err(TooManyBitsRequested) }
149 if self.bits < nbits {
150 if let Err(err) = self.refill() { return Err(err) }
151 if self.bits < nbits { return Err(BitstreamEnd) }
153 let res = self.read_cache_s(nbits);
154 self.skip_cache(nbits);
158 pub fn read_bool(&mut self) -> BitReaderResult<bool> {
160 if let Err(err) = self.refill() { return Err(err) }
161 if self.bits < 1 { return Err(BitstreamEnd) }
163 let res = self.read_cache(1);
168 pub fn peek(&mut self, nbits: u8) -> u32 {
169 if nbits > 32 { return 0 }
170 if self.bits < nbits { let _ = self.refill(); }
171 self.read_cache(nbits)
174 pub fn skip(&mut self, nbits: u32) -> BitReaderResult<()> {
175 if self.bits as u32 >= nbits {
176 self.skip_cache(nbits as u8);
179 let mut skip_bits = nbits - (self.bits as u32);
181 self.pos += ((skip_bits / 32) * 4) as usize;
182 skip_bits = skip_bits & 0x1F;
185 self.skip_cache(skip_bits as u8);
190 pub fn seek(&mut self, nbits: u32) -> BitReaderResult<()> {
191 if ((nbits + 7) >> 3) as usize > self.end { return Err(TooManyBitsRequested); }
193 self.pos = ((nbits / 32) * 4) as usize;
194 self.skip(nbits & 0x1F)
204 const DATA: [u8; 18] = [0b00011011; 18];
206 let mut br = BitReader::new(src, src.len(), BitReaderMode::LE16MSB);
209 assert_eq!(br.read(16).unwrap(), 0x1B1B);
211 const DATA2: [u8; 1] = [ 0b00011011 ];
213 let mut br = BitReader::new(src, src.len(), BitReaderMode::LE);
214 assert_eq!(br.read_s(5).unwrap(), -5);