1 /* bits.c -- output variable-length bit strings
2 * Copyright (C) 1992-1993 Jean-loup Gailly
3 * This is free software; you can redistribute it and/or modify it under the
4 * terms of the GNU General Public License, see the file COPYING.
11 * Output variable-length bit strings. Compression can be done
12 * to a file or to memory. (The latter is not supported in this version.)
16 * The PKZIP "deflate" file format interprets compressed file data
17 * as a sequence of bits. Multi-bit strings in the file may cross
18 * byte boundaries without restriction.
20 * The first bit of each byte is the low-order bit.
22 * The routines in this file allow a variable-length bit value to
23 * be output right-to-left (useful for literal values). For
24 * left-to-right output (useful for code strings from the tree routines),
25 * the bits must have been reversed first with bi_reverse().
27 * For in-memory compression, the compressed bit stream goes directly
28 * into the requested output buffer. The input data is read in blocks
29 * by the mem_read() function. The buffer is limited to 64K on 16 bit
34 * void bi_init (FILE *zipfile)
35 * Initialize the bit string routines.
37 * void send_bits (int value, int length)
38 * Write out a bit string, taking the source bits right to
41 * int bi_reverse (int value, int length)
42 * Reverse the bits of a bit string, taking the source bits left to
43 * right and emitting them right to left.
45 * void bi_windup (void)
46 * Write out any remaining bits in an incomplete byte.
48 * void copy_block(char *buf, unsigned len, int header)
49 * Copy a stored block to the zip file, storing first the length and
50 * its one's complement if requested.
64 static char rcsid[] = "$Id: bits.c,v 0.9 1993/06/11 10:16:58 jloup Exp $";
67 /* ===========================================================================
68 * Local data used by the "bit string" routines.
71 local file_t zfile; /* output gzip file */
73 local unsigned short bi_buf;
74 /* Output buffer. bits are inserted starting at the bottom (least significant
78 #define Buf_size (8 * 2*sizeof(char))
79 /* Number of bits used within bi_buf. (bi_buf might be implemented on
80 * more than 16 bits on some systems.)
84 /* Number of valid bits in bi_buf. All bits above the last valid bit
88 int (*read_buf) OF((char *buf, unsigned size));
89 /* Current input function. Set to mem_read for in-memory compression */
92 off_t bits_sent; /* bit length of the compressed data */
95 /* ===========================================================================
96 * Initialize the bit string routines.
98 void bi_init (zipfile)
99 file_t zipfile; /* output zip file, NO_FILE for in-memory compression */
108 /* Set the defaults for file compression. They are set by memcompress
109 * for in-memory compression.
111 if (zfile != NO_FILE) {
112 read_buf = file_read;
116 /* ===========================================================================
117 * Send a value on a given number of bits.
118 * IN assertion: length <= 16 and value fits in length bits.
120 void send_bits(value, length)
121 int value; /* value to send */
122 int length; /* number of bits */
125 Tracev((stderr," l %2d v %4x ", length, value));
126 Assert(length > 0 && length <= 15, "invalid length");
127 bits_sent += (off_t)length;
129 /* If not enough room in bi_buf, use (valid) bits from bi_buf and
130 * (16 - bi_valid) bits from value, leaving (width - (16-bi_valid))
131 * unused bits in value.
133 if (bi_valid > (int)Buf_size - length) {
134 bi_buf |= (value << bi_valid);
136 bi_buf = (ush)value >> (Buf_size - bi_valid);
137 bi_valid += length - Buf_size;
139 bi_buf |= value << bi_valid;
144 /* ===========================================================================
145 * Reverse the first len bits of a code, using straightforward code (a faster
146 * method would use a table)
147 * IN assertion: 1 <= len <= 15
149 unsigned bi_reverse(code, len)
150 unsigned code; /* the value to invert */
151 int len; /* its bit length */
153 register unsigned res = 0;
156 code >>= 1, res <<= 1;
161 /* ===========================================================================
162 * Write out any remaining bits in an incomplete byte.
168 } else if (bi_valid > 0) {
174 bits_sent = (bits_sent+7) & ~7;
178 /* ===========================================================================
179 * Copy a stored block to the zip file, storing first the length and its
180 * one's complement if requested.
182 void copy_block(buf, len, header)
183 char *buf; /* the input data */
184 unsigned len; /* its length */
185 int header; /* true if block header must be written */
187 bi_windup(); /* align on byte boundary */
191 put_short((ush)~len);
197 bits_sent += (off_t)len<<3;
202 if (key) zencode(*buf, t);