/*
* 11/19/04 1.0 moved to LGPL.
*
* 12/12/99 0.0.7 Implementation stores single bits
* as ints for better performance. mdm@techie.com.
*
* 02/28/99 0.0 Java Conversion by E.B, javalayer@javazoom.net
*
* 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.
* <p>
* 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.
* <p>
*/
// 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];
@SuppressWarnings("unused")
private int buf_bit_idx;
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;
}
}