about summary refs log tree commit diff
path: root/lib/bitio.c
blob: ca1b55f94f22a7334cf9e4e2c62b30c64acb8ba2 (plain) (blame)
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
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
/*\
 * $Id: bitio.c,v 1.5 1992/11/24 19:36:46 dws Exp dws $
 *
 * bitio.c - bitstream I/O
 *
 * Works for (sizeof(unsigned long)-1)*8 bits.
 *
 * Copyright (C) 1992 by David W. Sanderson.
 * 
 * Permission to use, copy, modify, and distribute this software and its
 * documentation for any purpose and without fee is hereby granted,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  This software is provided "as is"
 * without express or implied warranty.
 *
 * $Log: bitio.c,v $
 * Revision 1.5  1992/11/24  19:36:46  dws
 * Added copyright.
 *
 * Revision 1.4  1992/11/17  03:37:50  dws
 * updated comment
 *
 * Revision 1.3  1992/11/10  23:15:16  dws
 * Removed superfluous code.
 *
 * Revision 1.2  1992/11/10  23:11:22  dws
 * Generalized to handle more than one bitstream at once.
 *
 * Revision 1.1  1992/11/10  18:33:21  dws
 * Initial revision
 *
\*/

#include <string.h>

#include "bitio.h"

struct bitstream
{
    FILE *
        f;      /* bytestream */
    unsigned long
        bitbuf;     /* bit buffer */
    int
        nbitbuf;    /* number of bits in 'bitbuf' */
    char
        mode;
};

#define Mask(n)     ((1<<(n))-1)

#define BitPut(b,ul,n)  ((b)->bitbuf = (((b)->bitbuf<<(n))  \
                    |((ul)&Mask(n))),   \
            (b)->nbitbuf += (n))

#define BitGet(b,n) (((b)->bitbuf>>((b)->nbitbuf-=(n))) & Mask(n))

/*
 * pm_bitinit() - allocate and return a struct bitstream * for the
 * given FILE*.
 *
 * mode must be one of "r" or "w", according to whether you will be
 * reading from or writing to the struct bitstream *.
 *
 * Returns 0 on error.
 */

struct bitstream *
pm_bitinit(FILE * const f, const char * const mode) {

    struct bitstream * ans;

    if (!f || !mode)
        ans = NULL;
    else if (strcmp(mode, "r") != 0 && strcmp(mode, "w") != 0)
        ans = NULL;
    else {
        ans = (struct bitstream *)calloc(1, sizeof(struct bitstream));
        if (ans != NULL) {
            ans->f = f;
            ans->mode = *mode;
        }
    }
    return ans;
}

/*
 * pm_bitfini() - deallocate the given struct bitstream *.
 *
 * You must call this after you are done with the struct bitstream *.
 * 
 * It may flush some bits left in the buffer.
 *
 * Returns the number of bytes written, -1 on error.
 */

int
pm_bitfini(b)
    struct bitstream *b;
{
    int     nbyte = 0;

    if(!b)
        return -1;

    /* flush the output */
    if(b->mode == 'w')
    {
        /* flush the bits */
        if (b->nbitbuf < 0 || b->nbitbuf >= 8)
        {
            /* pm_bitwrite() didn't work */
            return -1;
        }

        /*
         * If we get to here, nbitbuf is 0..7
         */
        if(b->nbitbuf)
        {
            char    c;

            BitPut(b, 0, (long)8-(b->nbitbuf));
            c = (char) BitGet(b, (long)8);
            if(putc(c, b->f) == EOF)
            {
                return -1;
            }
            nbyte++;
        }
    }

    free(b);
    return nbyte;
}

/*
 * pm_bitread() - read the next nbits into *val from the given file.
 * 
 * The last pm_bitread() must be followed by a call to pm_bitfini().
 * 
 * Returns the number of bytes read, -1 on error.
 */

int 
pm_bitread(b, nbits, val)
    struct bitstream *b;
    unsigned long   nbits;
    unsigned long  *val;
{
    int     nbyte = 0;
    int     c;

    if(!b)
        return -1;

    while (b->nbitbuf < nbits)
    {
        if((c = getc(b->f)) == EOF)
        {
            return -1;
        }
        nbyte++;

        BitPut(b, c, (long) 8);
    }

    *val = BitGet(b, nbits);
    return nbyte;
}

/*
 * pm_bitwrite() - write the low nbits of val to the given file.
 * 
 * The last pm_bitwrite() must be followed by a call to pm_bitfini().
 * 
 * Returns the number of bytes written, -1 on error.
 */

int
pm_bitwrite(b, nbits, val)
    struct bitstream *b;
    unsigned long   nbits;
    unsigned long   val;
{
    int     nbyte = 0;
    char        c;

    if(!b)
        return -1;

    BitPut(b, val, nbits);

    while (b->nbitbuf >= 8)
    {
        c = (char) BitGet(b, (long)8);

        if(putc(c, b->f) == EOF)
        {
            return -1;
        }
        nbyte++;
    }

    return nbyte;
}