bits.c

   1 /* bits.c -- output variable-length bit strings
   2
   3    Copyright (C) 1999, 2009-2024 Free Software Foundation, Inc.
   4    Copyright (C) 1992-1993 Jean-loup Gailly
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3, or (at your option)
   9    any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program; if not, write to the Free Software Foundation,
  18    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  19
  20
  21 /*
  22  *  PURPOSE
  23  *
  24  *      Output variable-length bit strings. Compression can be done
  25  *      to a file or to memory. (The latter is not supported in this version.)
  26  *
  27  *  DISCUSSION
  28  *
  29  *      The PKZIP "deflate" file format interprets compressed file data
  30  *      as a sequence of bits.  Multi-bit strings in the file may cross
  31  *      byte boundaries without restriction.
  32  *
  33  *      The first bit of each byte is the low-order bit.
  34  *
  35  *      The routines in this file allow a variable-length bit value to
  36  *      be output right-to-left (useful for literal values). For
  37  *      left-to-right output (useful for code strings from the tree routines),
  38  *      the bits must have been reversed first with bi_reverse().
  39  *
  40  *      For in-memory compression, the compressed bit stream goes directly
  41  *      into the requested output buffer. The input data is read in blocks
  42  *      by the mem_read() function. The buffer is limited to 64K on 16 bit
  43  *      machines.
  44  *
  45  *  INTERFACE
  46  *
  47  *      void bi_init (FILE *zipfile)
  48  *          Initialize the bit string routines.
  49  *
  50  *      void send_bits (int value, int length)
  51  *          Write out a bit string, taking the source bits right to
  52  *          left.
  53  *
  54  *      int bi_reverse (int value, int length)
  55  *          Reverse the bits of a bit string, taking the source bits left to
  56  *          right and emitting them right to left.
  57  *
  58  *      void bi_windup ()
  59  *          Write out any remaining bits in an incomplete byte.
  60  *
  61  *      void copy_block(char *buf, unsigned len, int header)
  62  *          Copy a stored block to the zip file, storing first the length and
  63  *          its one's complement if requested.
  64  *
  65  */
  66
  67 #include <config.h>
  68 #include "tailor.h"
  69 #include "gzip.h"
  70
  71 #ifdef DEBUG
  72 #  include <stdio.h>
  73 #endif
  74
  75 /* ===========================================================================
  76  * Local data used by the "bit string" routines.
  77  */
  78
  79 static file_t zfile; /* output gzip file */
  80
  81 #ifndef IBM_Z_DFLTCC
  82 static
  83 #endif
  84 unsigned short bi_buf;
  85 /* Output buffer. bits are inserted starting at the bottom (least significant
  86  * bits).
  87  */
  88
  89 #define Buf_size (8 * 2*sizeof(char))
  90 /* Number of bits used within bi_buf. (bi_buf might be implemented on
  91  * more than 16 bits on some systems.)
  92  */
  93
  94 #ifndef IBM_Z_DFLTCC
  95 static
  96 #endif
  97 int bi_valid;
  98 /* Number of valid bits in bi_buf.  All bits above the last valid bit
  99  * are always zero.
 100  */
 101
 102 int (*read_buf) (char *buf, unsigned size);
 103 /* Current input function. Set to mem_read for in-memory compression */
 104
 105 #ifdef DEBUG
 106   off_t bits_sent;   /* bit length of the compressed data */
 107 #endif
 108
 109 /* ===========================================================================
 110  * Initialize the bit string routines.
 111  * ZIPFILE is the output zip file; it is NO_FILE for in-memory compression.
 112  */
 113 void
 114 bi_init (file_t zipfile)
 115 {
 116     zfile  = zipfile;
 117     bi_buf = 0;
 118     bi_valid = 0;
 119 #ifdef DEBUG
 120     bits_sent = 0L;
 121 #endif
 122
 123     /* Set the defaults for file compression. They are set by memcompress
 124      * for in-memory compression.
 125      */
 126     if (zfile != NO_FILE) {
 127         read_buf  = file_read;
 128     }
 129 }
 130
 131 /* ===========================================================================
 132  * Send VALUE on LENGTH bits.
 133  * IN assertion: LENGTH <= 16 and VALUE fits in LENGTH bits.
 134  */
 135 void
 136 send_bits (int value, int length)
 137 {
 138 #ifdef DEBUG
 139     Tracev ((stderr, " l %2d v %4x ", length, value + 0u));
 140     Assert(length > 0 && length <= 15, "invalid length");
 141     bits_sent += (off_t)length;
 142 #endif
 143     /* If not enough room in bi_buf, use (valid) bits from bi_buf and
 144      * (16 - bi_valid) bits from value, leaving (width - (16-bi_valid))
 145      * unused bits in value.
 146      */
 147     if (bi_valid > (int)Buf_size - length) {
 148         bi_buf |= (value << bi_valid);
 149         put_short(bi_buf);
 150         bi_buf = (ush)value >> (Buf_size - bi_valid);
 151         bi_valid += length - Buf_size;
 152     } else {
 153         bi_buf |= value << bi_valid;
 154         bi_valid += length;
 155     }
 156 }
 157
 158 /* ===========================================================================
 159  * Reverse the first LEN bits of CODE, using straightforward code (a faster
 160  * method would use a table)
 161  * IN assertion: 1 <= LEN <= 15
 162  */
 163 unsigned
 164 bi_reverse (unsigned code, int len)
 165 {
 166     register unsigned res = 0;
 167     do {
 168         res |= code & 1;
 169         code >>= 1, res <<= 1;
 170     } while (--len > 0);
 171     return res >> 1;
 172 }
 173
 174 /* ===========================================================================
 175  * Write out any remaining bits in an incomplete byte.
 176  */
 177 void
 178 bi_windup ()
 179 {
 180     if (bi_valid > 8) {
 181         put_short(bi_buf);
 182     } else if (bi_valid > 0) {
 183         put_byte(bi_buf);
 184     }
 185     bi_buf = 0;
 186     bi_valid = 0;
 187 #ifdef DEBUG
 188     bits_sent = (bits_sent+7) & ~7;
 189 #endif
 190 }
 191
 192 /* ===========================================================================
 193  * Copy a stored block to the zip file, storing first the length and its
 194  * one's complement if requested.  BUF is the input data of length
 195  * LEN; HEADER is true if block header must be written.
 196  */
 197 void
 198 copy_block (char *buf, unsigned len, int header)
 199 {
 200     bi_windup();              /* align on byte boundary */
 201
 202     if (header) {
 203         put_short((ush)len);
 204         put_short((ush)~len);
 205 #ifdef DEBUG
 206         bits_sent += 2*16;
 207 #endif
 208     }
 209 #ifdef DEBUG
 210     bits_sent += (off_t)len<<3;
 211 #endif
 212     while (len--) {
 213         put_byte(*buf++);
 214     }
 215 }