aboutsummaryrefslogtreecommitdiff
path: root/deps/libchdr/bitstream.c
blob: 3f61c938c347c81d68bd3d6c058e773666cd3e1e (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
/* license:BSD-3-Clause
 * copyright-holders:Aaron Giles
***************************************************************************

    bitstream.c

    Helper classes for reading/writing at the bit level.

***************************************************************************/

#include "bitstream.h"
#include <stdlib.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;
}