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]) {
54 let 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 self.cache |= nw << (32 - self.bits);
61 fn fill32le32(&mut self, src: &[u8], lsb: bool) {
62 let nw = (((src[3] as u32) << 24) |
63 ((src[2] as u32) << 16) |
64 ((src[1] as u32) << 8) |
65 ((src[0] as u32) << 0)) as u64;
67 self.cache |= nw << self.bits;
69 self.cache |= nw << (32 - self.bits);
74 fn refill(&mut self) -> BitReaderResult<()> {
75 if self.pos >= self.end { return Err(BitstreamEnd) }
76 while self.bits <= 32 {
77 if self.pos + 4 <= self.end {
78 let buf = &self.src[self.pos..];
80 BitReaderMode::BE => self.fill32be (buf),
81 BitReaderMode::LE16MSB => self.fill32le16(buf),
82 BitReaderMode::LE => self.fill32le32(buf, true),
83 BitReaderMode::LE32MSB => self.fill32le32(buf, false),
88 let mut buf: [u8; 4] = [0, 0, 0, 0];
89 let mut newbits: u8 = 0;
91 if self.pos < self.end {
92 buf[i] = self.src[self.pos];
93 self.pos = self.pos + 1;
97 if newbits == 0 { break; }
99 BitReaderMode::BE => self.fill32be (&buf),
100 BitReaderMode::LE16MSB => self.fill32le16(&buf),
101 BitReaderMode::LE => self.fill32le32(&buf, true),
102 BitReaderMode::LE32MSB => self.fill32le32(&buf, false),
104 self.bits += newbits;
111 fn read_cache(&mut self, nbits: u8) -> u32 {
112 let res = match self.mode {
113 BitReaderMode::LE => ((1u64 << nbits) - 1) & self.cache,
114 _ => (self.cache as u64) >> (64 - nbits),
119 fn read_cache_s(&mut self, nbits: u8) -> i32 {
120 let res = match self.mode {
121 BitReaderMode::LE => ((self.cache as i64) << (64 - nbits)) >> (64 - nbits),
122 _ => (self.cache as i64) >> (64 - nbits),
128 fn skip_cache(&mut self, nbits: u8) {
130 BitReaderMode::LE => self.cache >>= nbits,
131 _ => self.cache <<= nbits,
137 fn reset_cache(&mut self) {
143 pub fn read(&mut self, nbits: u8) -> BitReaderResult<u32> {
144 if nbits == 0 { return Ok(0) }
145 if nbits > 32 { return Err(TooManyBitsRequested) }
146 if self.bits < nbits {
147 if let Err(err) = self.refill() { return Err(err) }
148 if self.bits < nbits { return Err(BitstreamEnd) }
150 let res = self.read_cache(nbits);
151 self.skip_cache(nbits);
155 pub fn read_s(&mut self, nbits: u8) -> BitReaderResult<i32> {
156 if nbits == 0 || nbits > 32 { return Err(TooManyBitsRequested) }
157 if self.bits < nbits {
158 if let Err(err) = self.refill() { return Err(err) }
159 if self.bits < nbits { return Err(BitstreamEnd) }
161 let res = self.read_cache_s(nbits);
162 self.skip_cache(nbits);
167 pub fn read_bool(&mut self) -> BitReaderResult<bool> {
169 if let Err(err) = self.refill() { return Err(err) }
170 if self.bits < 1 { return Err(BitstreamEnd) }
172 let res = self.read_cache(1);
178 pub fn peek(&mut self, nbits: u8) -> u32 {
179 if nbits > 32 { return 0 }
180 if self.bits < nbits { let _ = self.refill(); }
181 self.read_cache(nbits)
185 pub fn skip(&mut self, nbits: u32) -> BitReaderResult<()> {
186 if self.bits as u32 >= nbits {
187 self.skip_cache(nbits as u8);
190 let mut skip_bits = nbits - (self.bits as u32);
192 self.pos += ((skip_bits / 32) * 4) as usize;
193 skip_bits = skip_bits & 0x1F;
196 self.skip_cache(skip_bits as u8);
201 pub fn seek(&mut self, nbits: u32) -> BitReaderResult<()> {
202 if ((nbits + 7) >> 3) as usize > self.end { return Err(TooManyBitsRequested); }
204 self.pos = ((nbits / 32) * 4) as usize;
205 self.skip(nbits & 0x1F)
208 pub fn align(&mut self) {
209 let pos = self.bits & 7;
211 self.skip_cache(pos);
216 pub fn reverse_bits(inval: u32, len: u8) -> u32 {
217 if len == 0 { return 0; }
218 const REV_TAB: [u8; 16] = [
219 0b0000, 0b1000, 0b0100, 0b1100, 0b0010, 0b1010, 0b0110, 0b1110,
220 0b0001, 0b1001, 0b0101, 0b1101, 0b0011, 0b1011, 0b0111, 0b1111,
226 ret = (ret << 4) | (REV_TAB[(val & 0xF) as usize] as u32);
238 const DATA: [u8; 18] = [0b00011011; 18];
240 let mut br = BitReader::new(src, src.len(), BitReaderMode::LE16MSB);
243 assert_eq!(br.read(16).unwrap(), 0x1B1B);
245 const DATA2: [u8; 1] = [ 0b00011011 ];
247 let mut br = BitReader::new(src, src.len(), BitReaderMode::LE);
248 assert_eq!(br.read_s(5).unwrap(), -5);