Commit | Line | Data |
---|---|---|
3719602c PC |
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 | * bitstream_peek - fetch the requested number of bits | |
39 | * but don't advance the input pointer | |
40 | *----------------------------------------------------- | |
41 | */ | |
42 | ||
43 | uint32_t bitstream_peek(struct bitstream* bitstream, int numbits) | |
44 | { | |
45 | if (numbits == 0) | |
46 | return 0; | |
47 | ||
48 | /* fetch data if we need more */ | |
49 | if (numbits > bitstream->bits) | |
50 | { | |
51 | while (bitstream->bits <= 24) | |
52 | { | |
53 | if (bitstream->doffset < bitstream->dlength) | |
54 | bitstream->buffer |= bitstream->read[bitstream->doffset] << (24 - bitstream->bits); | |
55 | bitstream->doffset++; | |
56 | bitstream->bits += 8; | |
57 | } | |
58 | } | |
59 | ||
60 | /* return the data */ | |
61 | return bitstream->buffer >> (32 - numbits); | |
62 | } | |
63 | ||
64 | /*----------------------------------------------------- | |
65 | * bitstream_remove - advance the input pointer by the | |
66 | * specified number of bits | |
67 | *----------------------------------------------------- | |
68 | */ | |
69 | ||
70 | void bitstream_remove(struct bitstream* bitstream, int numbits) | |
71 | { | |
72 | bitstream->buffer <<= numbits; | |
73 | bitstream->bits -= numbits; | |
74 | } | |
75 | ||
76 | /*----------------------------------------------------- | |
77 | * bitstream_read - fetch the requested number of bits | |
78 | *----------------------------------------------------- | |
79 | */ | |
80 | ||
81 | uint32_t bitstream_read(struct bitstream* bitstream, int numbits) | |
82 | { | |
83 | uint32_t result = bitstream_peek(bitstream, numbits); | |
84 | bitstream_remove(bitstream, numbits); | |
85 | return result; | |
86 | } | |
87 | ||
88 | /*------------------------------------------------- | |
89 | * read_offset - return the current read offset | |
90 | *------------------------------------------------- | |
91 | */ | |
92 | ||
93 | uint32_t bitstream_read_offset(struct bitstream* bitstream) | |
94 | { | |
95 | uint32_t result = bitstream->doffset; | |
96 | int bits = bitstream->bits; | |
97 | while (bits >= 8) | |
98 | { | |
99 | result--; | |
100 | bits -= 8; | |
101 | } | |
102 | return result; | |
103 | } | |
104 | ||
105 | /*------------------------------------------------- | |
106 | * flush - flush to the nearest byte | |
107 | *------------------------------------------------- | |
108 | */ | |
109 | ||
110 | uint32_t bitstream_flush(struct bitstream* bitstream) | |
111 | { | |
112 | while (bitstream->bits >= 8) | |
113 | { | |
114 | bitstream->doffset--; | |
115 | bitstream->bits -= 8; | |
116 | } | |
117 | bitstream->bits = bitstream->buffer = 0; | |
118 | return bitstream->doffset; | |
119 | } |