[pcsx_rearmed.git] / deps / libchdr / src / libchdr_bitstream.c

/* 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;
}
Commit	Line	Data
9c659ffe	1	/* license:BSD-3-Clause
	2	* copyright-holders:Aaron Giles
	3	***************************************************************************
ce188d4d	4
	5	bitstream.c
	6
	7	Helper classes for reading/writing at the bit level.
	8
	9	***************************************************************************/
	10
ce188d4d	11	#include <stdlib.h>
2ff0b512	12	#include <libchdr/bitstream.h>
ce188d4d	13
9c659ffe	14	/***************************************************************************
	15	* INLINE FUNCTIONS
	16	***************************************************************************
	17	*/
ce188d4d	18
	19	int bitstream_overflow(struct bitstream* bitstream) { return ((bitstream->doffset - bitstream->bits / 8) > bitstream->dlength); }
	20
9c659ffe	21	/*-------------------------------------------------
	22	* create_bitstream - constructor
	23	*-------------------------------------------------
	24	*/
ce188d4d	25
	26	struct bitstream* create_bitstream(const void *src, uint32_t srclength)
	27	{
	28	struct bitstream* bitstream = (struct bitstream*)malloc(sizeof(struct bitstream));
	29	bitstream->buffer = 0;
	30	bitstream->bits = 0;
	31	bitstream->read = (const uint8_t*)src;
	32	bitstream->doffset = 0;
	33	bitstream->dlength = srclength;
	34	return bitstream;
	35	}
	36
	37
9c659ffe	38	/*-----------------------------------------------------
	39	* bitstream_peek - fetch the requested number of bits
	40	* but don't advance the input pointer
	41	*-----------------------------------------------------
	42	*/
ce188d4d	43
	44	uint32_t bitstream_peek(struct bitstream* bitstream, int numbits)
	45	{
	46	if (numbits == 0)
	47	return 0;
	48
9c659ffe	49	/* fetch data if we need more */
ce188d4d	50	if (numbits > bitstream->bits)
	51	{
	52	while (bitstream->bits <= 24)
	53	{
	54	if (bitstream->doffset < bitstream->dlength)
	55	bitstream->buffer \|= bitstream->read[bitstream->doffset] << (24 - bitstream->bits);
	56	bitstream->doffset++;
	57	bitstream->bits += 8;
	58	}
	59	}
	60
9c659ffe	61	/* return the data */
ce188d4d	62	return bitstream->buffer >> (32 - numbits);
	63	}
	64
	65
9c659ffe	66	/*-----------------------------------------------------
	67	* bitstream_remove - advance the input pointer by the
	68	* specified number of bits
	69	*-----------------------------------------------------
	70	*/
ce188d4d	71
	72	void bitstream_remove(struct bitstream* bitstream, int numbits)
	73	{
	74	bitstream->buffer <<= numbits;
	75	bitstream->bits -= numbits;
	76	}
	77
	78
9c659ffe	79	/*-----------------------------------------------------
	80	* bitstream_read - fetch the requested number of bits
	81	*-----------------------------------------------------
	82	*/
ce188d4d	83
	84	uint32_t bitstream_read(struct bitstream* bitstream, int numbits)
	85	{
	86	uint32_t result = bitstream_peek(bitstream, numbits);
	87	bitstream_remove(bitstream, numbits);
	88	return result;
	89	}
	90
	91
9c659ffe	92	/*-------------------------------------------------
	93	* read_offset - return the current read offset
	94	*-------------------------------------------------
	95	*/
ce188d4d	96
	97	uint32_t bitstream_read_offset(struct bitstream* bitstream)
	98	{
	99	uint32_t result = bitstream->doffset;
	100	int bits = bitstream->bits;
	101	while (bits >= 8)
	102	{
	103	result--;
	104	bits -= 8;
	105	}
	106	return result;
	107	}
	108
	109
9c659ffe	110	/*-------------------------------------------------
	111	* flush - flush to the nearest byte
	112	*-------------------------------------------------
	113	*/
ce188d4d	114
	115	uint32_t bitstream_flush(struct bitstream* bitstream)
	116	{
	117	while (bitstream->bits >= 8)
	118	{
	119	bitstream->doffset--;
	120	bitstream->bits -= 8;
	121	}
	122	bitstream->bits = bitstream->buffer = 0;
	123	return bitstream->doffset;
	124	}
	125