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/* license:BSD-3-Clause
* copyright-holders:Aaron Giles
***************************************************************************
bitstream.c
Helper classes for reading/writing at the bit level.
***************************************************************************/
#include <stdlib.h>
#include <libchdr/bitstream.h>
/***************************************************************************
* INLINE FUNCTIONS
***************************************************************************
*/
int bitstream_overflow(struct bitstream* bitstream) { return ((bitstream->doffset - bitstream->bits / 8) > bitstream->dlength); }
/*-------------------------------------------------
* create_bitstream - constructor
*-------------------------------------------------
*/
struct bitstream* create_bitstream(const void *src, uint32_t srclength)
{
struct bitstream* bitstream = (struct bitstream*)malloc(sizeof(struct bitstream));
bitstream->buffer = 0;
bitstream->bits = 0;
bitstream->read = (const uint8_t*)src;
bitstream->doffset = 0;
bitstream->dlength = srclength;
return bitstream;
}
/*-----------------------------------------------------
* bitstream_peek - fetch the requested number of bits
* but don't advance the input pointer
*-----------------------------------------------------
*/
uint32_t bitstream_peek(struct bitstream* bitstream, int numbits)
{
if (numbits == 0)
return 0;
/* fetch data if we need more */
if (numbits > bitstream->bits)
{
while (bitstream->bits <= 24)
{
if (bitstream->doffset < bitstream->dlength)
bitstream->buffer |= bitstream->read[bitstream->doffset] << (24 - bitstream->bits);
bitstream->doffset++;
bitstream->bits += 8;
}
}
/* return the data */
return bitstream->buffer >> (32 - numbits);
}
/*-----------------------------------------------------
* bitstream_remove - advance the input pointer by the
* specified number of bits
*-----------------------------------------------------
*/
void bitstream_remove(struct bitstream* bitstream, int numbits)
{
bitstream->buffer <<= numbits;
bitstream->bits -= numbits;
}
/*-----------------------------------------------------
* bitstream_read - fetch the requested number of bits
*-----------------------------------------------------
*/
uint32_t bitstream_read(struct bitstream* bitstream, int numbits)
{
uint32_t result = bitstream_peek(bitstream, numbits);
bitstream_remove(bitstream, numbits);
return result;
}
/*-------------------------------------------------
* read_offset - return the current read offset
*-------------------------------------------------
*/
uint32_t bitstream_read_offset(struct bitstream* bitstream)
{
uint32_t result = bitstream->doffset;
int bits = bitstream->bits;
while (bits >= 8)
{
result--;
bits -= 8;
}
return result;
}
/*-------------------------------------------------
* flush - flush to the nearest byte
*-------------------------------------------------
*/
uint32_t bitstream_flush(struct bitstream* bitstream)
{
while (bitstream->bits >= 8)
{
bitstream->doffset--;
bitstream->bits -= 8;
}
bitstream->bits = bitstream->buffer = 0;
return bitstream->doffset;
}
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