javazoom.jl.decoder.BitReserve Maven / Gradle / Ivy
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/*
* 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];
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;
}
}