javazoom.jl.decoder.BitReserve Maven / Gradle / Ivy
/*
* 11/19/04 1.0 moved to LGPL.
*
* 12/12/99 0.0.7 Implementation stores single bits as ints for better performance. [email protected].
*
* 02/28/99 0.0 Java Conversion by E.B, [email protected]
*
* Adapted from the public c code by Jeff Tsay.
*
* ----------------------------------------------------------------------- This program is free software; you can redistribute it
* and/or modify it under the terms of the GNU Library General Public License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public License along with this program; if not, write to the Free
* Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
* ----------------------------------------------------------------------
*/
package javazoom.jl.decoder;
/**
* Implementation of Bit Reservoir for Layer III.
*
* The implementation stores single bits as a word in the buffer. If a bit is set, the corresponding word in the buffer will be
* non-zero. If a bit is clear, the corresponding word is zero. Although this may seem waseful, this can be a factor of two
* quicker than packing 8 bits to a byte and extracting.
*
*/
// REVIEW: there is no range checking, so buffer underflow or overflow
// can silently occur.
final class BitReserve {
/**
* Size of the internal buffer to store the reserved bits. Must be a power of 2. And x8, as each bit is stored as a single
* entry.
*/
private static final int BUFSIZE = 4096 * 8;
/**
* Mask that can be used to quickly implement the modulus operation on BUFSIZE.
*/
private static final int BUFSIZE_MASK = BUFSIZE - 1;
private int offset, totbit, buf_byte_idx;
private final int[] buf = new int[BUFSIZE];
BitReserve () {
offset = 0;
totbit = 0;
buf_byte_idx = 0;
}
/**
* Return totbit Field.
*/
public int hsstell () {
return totbit;
}
/**
* Read a number bits from the bit stream.
* @param N the number of
*/
public int hgetbits (int N) {
totbit += N;
int val = 0;
int pos = buf_byte_idx;
if (pos + N < BUFSIZE)
while (N-- > 0) {
val <<= 1;
val |= buf[pos++] != 0 ? 1 : 0;
}
else
while (N-- > 0) {
val <<= 1;
val |= buf[pos] != 0 ? 1 : 0;
pos = pos + 1 & BUFSIZE_MASK;
}
buf_byte_idx = pos;
return val;
}
/**
* Read 1 bit from the bit stream.
*/
/*
* public int hget1bit_old() { int val; totbit++; if (buf_bit_idx == 0) { buf_bit_idx = 8; buf_byte_idx++; } // BUFSIZE = 4096
* = 2^12, so // buf_byte_idx%BUFSIZE == buf_byte_idx & 0xfff val = buf[buf_byte_idx & BUFSIZE_MASK] & putmask[buf_bit_idx];
* buf_bit_idx--; val = val >>> buf_bit_idx; return val; }
*/
/**
* Returns next bit from reserve.
* @returns 0 if next bit is reset, or 1 if next bit is set.
*/
public int hget1bit () {
totbit++;
int val = buf[buf_byte_idx];
buf_byte_idx = buf_byte_idx + 1 & BUFSIZE_MASK;
return val;
}
/**
* Retrieves bits from the reserve.
*/
/*
* public int readBits(int[] out, int len) { if (buf_bit_idx == 0) { buf_bit_idx = 8; buf_byte_idx++; current =
* buf[buf_byte_idx & BUFSIZE_MASK]; }
*
*
*
* // save total number of bits returned len = buf_bit_idx; buf_bit_idx = 0;
*
* int b = current; int count = len-1;
*
* while (count >= 0) { out[count--] = (b & 0x1); b >>>= 1; }
*
* totbit += len; return len; }
*/
/**
* Write 8 bits into the bit stream.
*/
public void hputbuf (int val) {
int ofs = offset;
buf[ofs++] = val & 0x80;
buf[ofs++] = val & 0x40;
buf[ofs++] = val & 0x20;
buf[ofs++] = val & 0x10;
buf[ofs++] = val & 0x08;
buf[ofs++] = val & 0x04;
buf[ofs++] = val & 0x02;
buf[ofs++] = val & 0x01;
if (ofs == BUFSIZE)
offset = 0;
else
offset = ofs;
}
/**
* Rewind N bits in Stream.
*/
public void rewindNbits (int N) {
totbit -= N;
buf_byte_idx -= N;
if (buf_byte_idx < 0) buf_byte_idx += BUFSIZE;
}
/**
* Rewind N bytes in Stream.
*/
public void rewindNbytes (int N) {
int bits = N << 3;
totbit -= bits;
buf_byte_idx -= bits;
if (buf_byte_idx < 0) buf_byte_idx += BUFSIZE;
}
}