kolibrios/programs/media/ac97 mp3/trunk/mp3dec/bstream.c

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/* max bits required for any lookup - change if htable changes */
/* quad required 10 bit w/signs must have (MAXBITS+2) >= 10 */
#define MAXBITS 9
static unsigned int bitbuf;
static int bits;
static unsigned char *bs_ptr;
static unsigned char *bs_ptr0;
static unsigned char *bs_ptr_end; // optional for overrun test
void bitget_init(unsigned char *buf)
{
bs_ptr0 = bs_ptr = buf;
bits = 0;
bitbuf = 0;
}
int bitget(int n)
{
unsigned int x;
if (bits < n)
{ /* refill bit buf if necessary */
while (bits <= 24)
{
bitbuf = (bitbuf << 8) | *bs_ptr++;
bits += 8;
}
}
bits -= n;
x = bitbuf >> bits;
bitbuf -= x << bits;
return x;
}
void bitget_skip(int n)
{
unsigned int k;
if (bits < n)
{
n -= bits;
k = n >> 3;
/*--- bytes = n/8 --*/
bs_ptr += k;
n -= k << 3;
bitbuf = *bs_ptr++;
bits = 8;
}
bits -= n;
bitbuf -= (bitbuf >> bits) << bits;
}
void bitget_init_end(unsigned char *buf_end)
{
bs_ptr_end = buf_end;
}
/*------------- check overrun -------------*/
int bitget_overrun()
{
return bs_ptr > bs_ptr_end;
}
/*------------- get n bits from bitstream -------------*/
int bitget_bits_used()
{
unsigned int n; /* compute bits used from last init call */
n = ((bs_ptr - bs_ptr0) << 3) - bits;
return n;
}
/*------------- check for n bits in bitbuf -------------*/
void bitget_check(int n)
{
if (bits < n)
{
while (bits <= 24)
{
bitbuf = (bitbuf << 8) | *bs_ptr++;
bits += 8;
}
}
}
#if 0
/*------------- get 1 bit from bitstream -------------*/
int bitget_1bit()
{
unsigned int x;
if (bits <= 0)
{ /* refill bit buf if necessary */
while (bits <= 24)
{
bitbuf = (bitbuf << 8) | *bs_ptr++;
bits += 8;
}
}
bits--;
x = bitbuf >> bits;
bitbuf -= x << bits;
return x;
}
/*------------- get 1 bit from bitstream NO CHECK -------------*/
int bitget_1bit()
{
unsigned int x;
bits--;
x = bitbuf >> bits;
bitbuf -= x << bits;
return x;
}
#endif
/* only huffman */
/*----- get n bits - checks for n+2 avail bits (linbits+sign) -----*/
int bitget_lb(int n)
{
unsigned int x;
if (bits < (n + 2))
{ /* refill bit buf if necessary */
while (bits <= 24)
{
bitbuf = (bitbuf << 8) | *bs_ptr++;
bits += 8;
}
}
bits -= n;
x = bitbuf >> bits;
bitbuf -= x << bits;
return x;
}
/*------------- get n bits but DO NOT remove from bitstream --*/
int bitget2(int n)
{
unsigned int x;
if (bits < (MAXBITS + 2))
{ /* refill bit buf if necessary */
while (bits <= 24)
{
bitbuf = (bitbuf << 8) | *bs_ptr++;
bits += 8;
}
}
x = bitbuf >> (bits - n);
return x;
}
/*------------- remove n bits from bitstream ---------*/
void bitget_purge(int n)
{
bits -= n;
bitbuf -= (bitbuf >> bits) << bits;
}
void mac_bitget_check(int n)
{
if( bits < n ) {
while( bits <= 24 ) {
bitbuf = (bitbuf << 8) | *bs_ptr++;
bits += 8;
}
}
}
int mac_bitget(int n)
{
unsigned int code;
bits -= n;
code = bitbuf >> bits;
bitbuf -= code << bits;
return code;
}
int mac_bitget2(int n)
{
return (bitbuf >> (bits-n));
}
int mac_bitget_1bit()
{
unsigned int code;
bits--;
code = bitbuf >> bits;
bitbuf -= code << bits;
return code;
}
void mac_bitget_purge(int n)
{
bits -= n;
bitbuf -= (bitbuf >> bits) << bits;
}
/*
#define mac_bitget(n) ( bits -= n, \
code = bitbuf >> bits, \
bitbuf -= code << bits, \
code )
#define mac_bitget_1bit() ( bits--, \
code = bitbuf >> bits, \
bitbuf -= code << bits, \
code )
*/