Book a Demo!
CoCalc Logo Icon
StoreFeaturesDocsShareSupportNewsAboutPoliciesSign UpSign In
stenzek
GitHub Repository: stenzek/duckstation
 Path: blob/master/dep/libchdr/src/libchdr_bitstream.c
4251 views
1
/* license:BSD-3-Clause

2
 * copyright-holders:Aaron Giles

3
***************************************************************************

4


5
    bitstream.c

6


7
    Helper classes for reading/writing at the bit level.

8


9
***************************************************************************/

10


11
#include <stdlib.h>

12
#include <libchdr/bitstream.h>

13


14
/***************************************************************************

15
 *  INLINE FUNCTIONS

16
 ***************************************************************************

17
 */

18


19
int bitstream_overflow(struct bitstream* bitstream) { return ((bitstream->doffset - bitstream->bits / 8) > bitstream->dlength); }

20


21
/*-------------------------------------------------

22
 *  create_bitstream - constructor

23
 *-------------------------------------------------

24
 */

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


38
/*-----------------------------------------------------

39
 *  bitstream_peek - fetch the requested number of bits

40
 *  but don't advance the input pointer

41
 *-----------------------------------------------------

42
 */

43


44
uint32_t bitstream_peek(struct bitstream* bitstream, int numbits)

45
{

46
	if (numbits == 0)

47
		return 0;

48


49
	/* fetch data if we need more */

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


61
	/* return the data */

62
	return bitstream->buffer >> (32 - numbits);

63
}

64


65


66
/*-----------------------------------------------------

67
 *  bitstream_remove - advance the input pointer by the

68
 *  specified number of bits

69
 *-----------------------------------------------------

70
 */

71


72
void bitstream_remove(struct bitstream* bitstream, int numbits)

73
{

74
	bitstream->buffer <<= numbits;

75
	bitstream->bits -= numbits;

76
}

77


78


79
/*-----------------------------------------------------

80
 *  bitstream_read - fetch the requested number of bits

81
 *-----------------------------------------------------

82
 */

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


92
/*-------------------------------------------------

93
 *  read_offset - return the current read offset

94
 *-------------------------------------------------

95
 */

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


110
/*-------------------------------------------------

111
 *  flush - flush to the nearest byte

112
 *-------------------------------------------------

113
 */

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


126


127