206 lines
5.7 KiB
C
206 lines
5.7 KiB
C
/* bits.c -- output variable-length bit strings
|
|
* Copyright (C) 1992-1993 Jean-loup Gailly
|
|
* This is free software; you can redistribute it and/or modify it under the
|
|
* terms of the GNU General Public License, see the file COPYING.
|
|
*/
|
|
|
|
|
|
/*
|
|
* PURPOSE
|
|
*
|
|
* Output variable-length bit strings. Compression can be done
|
|
* to a file or to memory. (The latter is not supported in this version.)
|
|
*
|
|
* DISCUSSION
|
|
*
|
|
* The PKZIP "deflate" file format interprets compressed file data
|
|
* as a sequence of bits. Multi-bit strings in the file may cross
|
|
* byte boundaries without restriction.
|
|
*
|
|
* The first bit of each byte is the low-order bit.
|
|
*
|
|
* The routines in this file allow a variable-length bit value to
|
|
* be output right-to-left (useful for literal values). For
|
|
* left-to-right output (useful for code strings from the tree routines),
|
|
* the bits must have been reversed first with bi_reverse().
|
|
*
|
|
* For in-memory compression, the compressed bit stream goes directly
|
|
* into the requested output buffer. The input data is read in blocks
|
|
* by the mem_read() function. The buffer is limited to 64K on 16 bit
|
|
* machines.
|
|
*
|
|
* INTERFACE
|
|
*
|
|
* void bi_init (FILE *zipfile)
|
|
* Initialize the bit string routines.
|
|
*
|
|
* void send_bits (int value, int length)
|
|
* Write out a bit string, taking the source bits right to
|
|
* left.
|
|
*
|
|
* int bi_reverse (int value, int length)
|
|
* Reverse the bits of a bit string, taking the source bits left to
|
|
* right and emitting them right to left.
|
|
*
|
|
* void bi_windup (void)
|
|
* Write out any remaining bits in an incomplete byte.
|
|
*
|
|
* void copy_block(char *buf, unsigned len, int header)
|
|
* Copy a stored block to the zip file, storing first the length and
|
|
* its one's complement if requested.
|
|
*
|
|
*/
|
|
|
|
#include "tailor.h"
|
|
#include "gzip.h"
|
|
#include "crypt.h"
|
|
|
|
#ifdef DEBUG
|
|
# include <stdio.h>
|
|
#endif
|
|
|
|
#ifdef RCSID
|
|
static char rcsid[] = "$Id: bits.c,v 1.3 1993/10/14 00:32:24 nate Exp $";
|
|
#endif
|
|
|
|
/* ===========================================================================
|
|
* Local data used by the "bit string" routines.
|
|
*/
|
|
|
|
local file_t zfile; /* output gzip file */
|
|
|
|
local unsigned short bi_buf;
|
|
/* Output buffer. bits are inserted starting at the bottom (least significant
|
|
* bits).
|
|
*/
|
|
|
|
#define Buf_size (8 * 2*sizeof(char))
|
|
/* Number of bits used within bi_buf. (bi_buf might be implemented on
|
|
* more than 16 bits on some systems.)
|
|
*/
|
|
|
|
local int bi_valid;
|
|
/* Number of valid bits in bi_buf. All bits above the last valid bit
|
|
* are always zero.
|
|
*/
|
|
|
|
int (*read_buf) OF((char *buf, unsigned size));
|
|
/* Current input function. Set to mem_read for in-memory compression */
|
|
|
|
#ifdef DEBUG
|
|
ulg bits_sent; /* bit length of the compressed data */
|
|
#endif
|
|
|
|
/* ===========================================================================
|
|
* Initialize the bit string routines.
|
|
*/
|
|
void bi_init (zipfile)
|
|
file_t zipfile; /* output zip file, NO_FILE for in-memory compression */
|
|
{
|
|
zfile = zipfile;
|
|
bi_buf = 0;
|
|
bi_valid = 0;
|
|
#ifdef DEBUG
|
|
bits_sent = 0L;
|
|
#endif
|
|
|
|
/* Set the defaults for file compression. They are set by memcompress
|
|
* for in-memory compression.
|
|
*/
|
|
if (zfile != NO_FILE) {
|
|
read_buf = file_read;
|
|
}
|
|
}
|
|
|
|
/* ===========================================================================
|
|
* Send a value on a given number of bits.
|
|
* IN assertion: length <= 16 and value fits in length bits.
|
|
*/
|
|
void send_bits(value, length)
|
|
int value; /* value to send */
|
|
int length; /* number of bits */
|
|
{
|
|
#ifdef DEBUG
|
|
Tracev((stderr," l %2d v %4x ", length, value));
|
|
Assert(length > 0 && length <= 15, "invalid length");
|
|
bits_sent += (ulg)length;
|
|
#endif
|
|
/* If not enough room in bi_buf, use (valid) bits from bi_buf and
|
|
* (16 - bi_valid) bits from value, leaving (width - (16-bi_valid))
|
|
* unused bits in value.
|
|
*/
|
|
if (bi_valid > (int)Buf_size - length) {
|
|
bi_buf |= (value << bi_valid);
|
|
put_short(bi_buf);
|
|
bi_buf = (ush)value >> (Buf_size - bi_valid);
|
|
bi_valid += length - Buf_size;
|
|
} else {
|
|
bi_buf |= value << bi_valid;
|
|
bi_valid += length;
|
|
}
|
|
}
|
|
|
|
/* ===========================================================================
|
|
* Reverse the first len bits of a code, using straightforward code (a faster
|
|
* method would use a table)
|
|
* IN assertion: 1 <= len <= 15
|
|
*/
|
|
unsigned bi_reverse(code, len)
|
|
unsigned code; /* the value to invert */
|
|
int len; /* its bit length */
|
|
{
|
|
register unsigned res = 0;
|
|
do {
|
|
res |= code & 1;
|
|
code >>= 1, res <<= 1;
|
|
} while (--len > 0);
|
|
return res >> 1;
|
|
}
|
|
|
|
/* ===========================================================================
|
|
* Write out any remaining bits in an incomplete byte.
|
|
*/
|
|
void bi_windup()
|
|
{
|
|
if (bi_valid > 8) {
|
|
put_short(bi_buf);
|
|
} else if (bi_valid > 0) {
|
|
put_byte(bi_buf);
|
|
}
|
|
bi_buf = 0;
|
|
bi_valid = 0;
|
|
#ifdef DEBUG
|
|
bits_sent = (bits_sent+7) & ~7;
|
|
#endif
|
|
}
|
|
|
|
/* ===========================================================================
|
|
* Copy a stored block to the zip file, storing first the length and its
|
|
* one's complement if requested.
|
|
*/
|
|
void copy_block(buf, len, header)
|
|
char *buf; /* the input data */
|
|
unsigned len; /* its length */
|
|
int header; /* true if block header must be written */
|
|
{
|
|
bi_windup(); /* align on byte boundary */
|
|
|
|
if (header) {
|
|
put_short((ush)len);
|
|
put_short((ush)~len);
|
|
#ifdef DEBUG
|
|
bits_sent += 2*16;
|
|
#endif
|
|
}
|
|
#ifdef DEBUG
|
|
bits_sent += (ulg)len<<3;
|
|
#endif
|
|
while (len--) {
|
|
#ifdef CRYPT
|
|
int t;
|
|
if (key) zencode(*buf, t);
|
|
#endif
|
|
put_byte(*buf++);
|
|
}
|
|
}
|