* Copyright (c) 1985, 1986, 1992, 1993

/* $NetBSD: zopen.c,v 1.16 2022/03/23 11:08:28 andvar Exp $ */

/*-
* Copyright (c) 1985, 1986, 1992, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Diomidis Spinellis and James A. Woods, derived from original
* work by Spencer Thomas and Joseph Orost.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/

#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static char sccsid[] = "@(#)zopen.c 8.1 (Berkeley) 6/27/93";
#else
static char rcsid[] = "$NetBSD: zopen.c,v 1.16 2022/03/23 11:08:28 andvar Exp $";
#endif
#endif /* LIBC_SCCS and not lint */

/*-
* fcompress.c - File compression ala IEEE Computer, June 1984.
*
* Compress authors:
* Spencer W. Thomas (decvax!utah-cs!thomas)
* Jim McKie (decvax!mcvax!jim)
* Steve Davies (decvax!vax135!petsd!peora!srd)
* Ken Turkowski (decvax!decwrl!turtlevax!ken)
* James A. Woods (decvax!ihnp4!ames!jaw)
* Joe Orost (decvax!vax135!petsd!joe)
*
* Cleaned up and converted to library returning I/O streams by
* Diomidis Spinellis <[email protected]>.
*
* zopen(filename, mode, bits)
* Returns a FILE * that can be used for read or write. The modes
* supported are only "r" and "w". Seeking is not allowed. On
* reading the file is decompressed, on writing it is compressed.
* The output is compatible with compress(1) with 16 bit tables.
* Any file produced by compress(1) can be read.
*/

#include <sys/param.h>
#include <sys/stat.h>

#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define BITS 16 /* Default bits. */
#define HSIZE 69001 /* 95% occupancy */

/* A code_int must be able to hold 2**BITS values of type int, and also -1. */
typedef long code_int;
typedef long count_int;

typedef u_char char_type;
static char_type magic_header[] =
{'\037', '\235'}; /* 1F 9D */

#define BIT_MASK 0x1f /* Defines for third byte of header. */
#define BLOCK_MASK 0x80

/*
* Masks 0x40 and 0x20 are free. I think 0x20 should mean that there is
* a fourth header byte (for expansion).
*/
#define INIT_BITS 9 /* Initial number of bits/code. */

#define MAXCODE(n_bits) ((1 << (n_bits)) - 1)

struct s_zstate {
FILE *zs_fp; /* File stream for I/O */
char zs_mode; /* r or w */
enum {
S_START, S_MIDDLE, S_EOF
} zs_state; /* State of computation */
int zs_n_bits; /* Number of bits/code. */
int zs_maxbits; /* User settable max # bits/code. */
code_int zs_maxcode; /* Maximum code, given n_bits. */
code_int zs_maxmaxcode; /* Should NEVER generate this code. */
count_int zs_htab [HSIZE];
u_short zs_codetab [HSIZE];
code_int zs_hsize; /* For dynamic table sizing. */
code_int zs_free_ent; /* First unused entry. */
/*
* Block compression parameters -- after all codes are used up,
* and compression rate changes, start over.
*/
int zs_block_compress;
int zs_clear_flg;
long zs_ratio;
count_int zs_checkpoint;
int zs_offset;
long zs_in_count; /* Length of input. */
long zs_bytes_out; /* Length of compressed output. */
long zs_out_count; /* # of codes output (for debugging). */
char_type zs_buf[BITS];
union {
struct {
long zs_fcode;
code_int zs_ent;
code_int zs_hsize_reg;
int zs_hshift;
} w; /* Write parameters */
struct {
char_type *zs_stackp;
int zs_finchar;
code_int zs_code, zs_oldcode, zs_incode;
int zs_roffset, zs_size;
char_type zs_gbuf[BITS];
} r; /* Read parameters */
} u;
};

/* Definitions to retain old variable names */
#define fp zs->zs_fp
#define zmode zs->zs_mode
#define state zs->zs_state
#define n_bits zs->zs_n_bits
#define maxbits zs->zs_maxbits
#define maxcode zs->zs_maxcode
#define maxmaxcode zs->zs_maxmaxcode
#define htab zs->zs_htab
#define codetab zs->zs_codetab
#define hsize zs->zs_hsize
#define free_ent zs->zs_free_ent
#define block_compress zs->zs_block_compress
#define clear_flg zs->zs_clear_flg
#define ratio zs->zs_ratio
#define checkpoint zs->zs_checkpoint
#define offset zs->zs_offset
#define in_count zs->zs_in_count
#define bytes_out zs->zs_bytes_out
#define out_count zs->zs_out_count
#define buf zs->zs_buf
#define fcode zs->u.w.zs_fcode
#define hsize_reg zs->u.w.zs_hsize_reg
#define ent zs->u.w.zs_ent
#define hshift zs->u.w.zs_hshift
#define stackp zs->u.r.zs_stackp
#define finchar zs->u.r.zs_finchar
#define code zs->u.r.zs_code
#define oldcode zs->u.r.zs_oldcode
#define incode zs->u.r.zs_incode
#define roffset zs->u.r.zs_roffset
#define size zs->u.r.zs_size
#define gbuf zs->u.r.zs_gbuf

/*
* To save much memory, we overlay the table used by compress() with those
* used by decompress(). The tab_prefix table is the same size and type as
* the codetab. The tab_suffix table needs 2**BITS characters. We get this
* from the beginning of htab. The output stack uses the rest of htab, and
* contains characters. There is plenty of room for any possible stack
* (stack used to be 8000 characters).
*/

#define htabof(i) htab[i]
#define codetabof(i) codetab[i]

#define tab_prefixof(i) codetabof(i)
#define tab_suffixof(i) ((char_type *)(htab))[i]
#define de_stack ((char_type *)&tab_suffixof(1 << BITS))

#define CHECK_GAP 10000 /* Ratio check interval. */

/*
* the next two codes should not be changed lightly, as they must not
* lie within the contiguous general code space.
*/
#define FIRST 257 /* First free entry. */
#define CLEAR 256 /* Table clear output code. */

static int cl_block(struct s_zstate *);
static code_int getcode(struct s_zstate *);
static int output(struct s_zstate *, code_int);
static int zclose(void *);
FILE *zopen(const char *, const char *, int);
static int zread(void *, char *, int);
static int zwrite(void *, const char *, int);

/*-
* Algorithm from "A Technique for High Performance Data Compression",
* Terry A. Welch, IEEE Computer Vol 17, No 6 (June 1984), pp 8-19.
*
* Algorithm:
* Modified Lempel-Ziv method (LZW). Basically finds common
* substrings and replaces them with a variable size code. This is
* deterministic, and can be done on the fly. Thus, the decompression
* procedure needs no input table, but tracks the way the table was built.
*/

/*-
* compress write
*
* Algorithm: use open addressing double hashing (no chaining) on the
* prefix code / next character combination. We do a variant of Knuth's
* algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
* secondary probe. Here, the modular division first probe is gives way
* to a faster exclusive-or manipulation. Also do block compression with
* an adaptive reset, whereby the code table is cleared when the compression
* ratio decreases, but after the table fills. The variable-length output
* codes are re-sized at this point, and a special CLEAR code is generated
* for the decompressor. Late addition: construct the table according to
* file size for noticeable speed improvement on small files. Please direct
* questions about this implementation to ames!jaw.
*/
static int
zwrite(void *cookie, const char *wbp, int num)
{
code_int i;
int c, disp;
struct s_zstate *zs;
const u_char *bp;
u_char tmp;
int count;

if (num == 0)
return (0);

zs = cookie;
count = num;
bp = (const u_char *)wbp;
if (state == S_MIDDLE)
goto middle;
state = S_MIDDLE;

maxmaxcode = 1L << maxbits;
if (fwrite(magic_header,
sizeof(char), sizeof(magic_header), fp) != sizeof(magic_header))
return (-1);
tmp = (u_char)(maxbits | block_compress);
if (fwrite(&tmp, sizeof(char), sizeof(tmp), fp) != sizeof(tmp))
return (-1);

offset = 0;
bytes_out = 3; /* Includes 3-byte header mojo. */
out_count = 0;
clear_flg = 0;
ratio = 0;
in_count = 1;
checkpoint = CHECK_GAP;
maxcode = MAXCODE(n_bits = INIT_BITS);
free_ent = ((block_compress) ? FIRST : 256);

ent = *bp++;
--count;

hshift = 0;
for (fcode = (long)hsize; fcode < 65536L; fcode *= 2L)
hshift++;
hshift = 8 - hshift; /* Set hash code range bound. */

hsize_reg = hsize;
memset(htab, 0xff, hsize_reg * sizeof(count_int));

middle: while (count--) {
c = *bp++;
in_count++;
fcode = (long)(((long)c << maxbits) + ent);
i = ((c << hshift) ^ ent); /* Xor hashing. */

if (htabof(i) == fcode) {
ent = codetabof(i);
continue;
} else if ((long)htabof(i) < 0) /* Empty slot. */
goto nomatch;
disp = hsize_reg - i; /* Secondary hash (after G. Knott). */
if (i == 0)
disp = 1;
probe: if ((i -= disp) < 0)
i += hsize_reg;

if (htabof(i) == fcode) {
ent = codetabof(i);
continue;
}
if ((long)htabof(i) >= 0)
goto probe;
nomatch: if (output(zs, (code_int) ent) == -1)
return (-1);
out_count++;
ent = c;
if (free_ent < maxmaxcode) {
codetabof(i) = free_ent++; /* code -> hashtable */
htabof(i) = fcode;
} else if ((count_int)in_count >=
checkpoint && block_compress) {
if (cl_block(zs) == -1)
return (-1);
}
}
return (num);
}

static int
zclose(void *cookie)
{
struct s_zstate *zs;
int rval;

zs = cookie;
if (zmode == 'w') { /* Put out the final code. */
if (output(zs, (code_int) ent) == -1) {
(void)fclose(fp);
free(zs);
return (-1);
}
out_count++;
if (output(zs, (code_int) - 1) == -1) {
(void)fclose(fp);
free(zs);
return (-1);
}
}
rval = fclose(fp) == EOF ? -1 : 0;
free(zs);
return (rval);
}

/*-
* Output the given code.
* Inputs:
* code: A n_bits-bit integer. If == -1, then EOF. This assumes
* that n_bits =< (long)wordsize - 1.
* Outputs:
* Outputs code to the file.
* Assumptions:
* Chars are 8 bits long.
* Algorithm:
* Maintain a BITS character long buffer (so that 8 codes will
* fit in it exactly). Use the VAX insv instruction to insert each
* code in turn. When the buffer fills up empty it and start over.
*/

static char_type lmask[9] =
{0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80, 0x00};
static char_type rmask[9] =
{0x00, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f, 0xff};

static int
output(struct s_zstate *zs, code_int ocode)
{
int bits, r_off;
char_type *bp;

r_off = offset;
bits = n_bits;
bp = buf;
if (ocode >= 0) {
/* Get to the first byte. */
bp += (r_off >> 3);
r_off &= 7;
/*
* Since ocode is always >= 8 bits, only need to mask the first
* hunk on the left.
*/
*bp = (*bp & rmask[r_off]) | ((ocode << r_off) & lmask[r_off]);
bp++;
bits -= (8 - r_off);
ocode >>= 8 - r_off;
/* Get any 8 bit parts in the middle (<=1 for up to 16 bits). */
if (bits >= 8) {
*bp++ = ocode;
ocode >>= 8;
bits -= 8;
}
/* Last bits. */
if (bits)
*bp = ocode;
offset += n_bits;
if (offset == (n_bits << 3)) {
bp = buf;
bits = n_bits;
bytes_out += bits;
if (fwrite(bp, sizeof(char), bits, fp) != (size_t)bits)
return (-1);
bp += bits;
bits = 0;
offset = 0;
}
/*
* If the next entry is going to be too big for the ocode size,
* then increase it, if possible.
*/
if (free_ent > maxcode || (clear_flg > 0)) {
/*
* Write the whole buffer, because the input side won't
* discover the size increase until after it has read it.
*/
if (offset > 0) {
if (fwrite(buf, 1, n_bits, fp) != (size_t)n_bits)
return (-1);
bytes_out += n_bits;
}
offset = 0;

if (clear_flg) {
maxcode = MAXCODE(n_bits = INIT_BITS);
clear_flg = 0;
} else {
n_bits++;
if (n_bits == maxbits)
maxcode = maxmaxcode;
else
maxcode = MAXCODE(n_bits);
}
}
} else {
/* At EOF, write the rest of the buffer. */
if (offset > 0) {
offset = (offset + 7) / 8;
if (fwrite(buf, 1, offset, fp) != (size_t)offset)
return (-1);
bytes_out += offset;
}
offset = 0;
}
return (0);
}

/*
* Decompress read. This routine adapts to the codes in the file building
* the "string" table on-the-fly; requiring no table to be stored in the
* compressed file. The tables used herein are shared with those of the
* compress() routine. See the definitions above.
*/
static int
zread(void *cookie, char *rbp, int num)
{
u_int count;
struct s_zstate *zs;
u_char *bp, header[3];

if (num == 0)
return (0);

zs = cookie;
count = num;
bp = (u_char *)rbp;
switch (state) {
case S_START:
state = S_MIDDLE;
break;
case S_MIDDLE:
goto middle;
case S_EOF:
goto eof;
}

/* Check the magic number */
if (fread(header,
sizeof(char), sizeof(header), fp) != sizeof(header) ||
memcmp(header, magic_header, sizeof(magic_header)) != 0) {
errno = EFTYPE;
return (-1);
}
maxbits = header[2]; /* Set -b from file. */
block_compress = maxbits & BLOCK_MASK;
maxbits &= BIT_MASK;
maxmaxcode = 1L << maxbits;
if (maxbits > BITS || maxbits < 12) {
errno = EFTYPE;
return (-1);
}
/* As above, initialize the first 256 entries in the table. */
maxcode = MAXCODE(n_bits = INIT_BITS);
for (code = 255; code >= 0; code--) {
tab_prefixof(code) = 0;
tab_suffixof(code) = (char_type) code;
}
free_ent = block_compress ? FIRST : 256;
oldcode = -1;
stackp = de_stack;

while ((code = getcode(zs)) > -1) {

if ((code == CLEAR) && block_compress) {
for (code = 255; code >= 0; code--)
tab_prefixof(code) = 0;
clear_flg = 1;
free_ent = FIRST;
oldcode = -1;
continue;
}
incode = code;

/* Special case for kWkWk string. */
if (code >= free_ent) {
if (code > free_ent || oldcode == -1) {
/* Bad stream. */
errno = EINVAL;
return (-1);
}
*stackp++ = finchar;
code = oldcode;
}
/*
* The above condition ensures that code < free_ent.
* The construction of tab_prefixof in turn guarantees that
* each iteration decreases code and therefore stack usage is
* bound by 1 << BITS - 256.
*/

/* Generate output characters in reverse order. */
while (code >= 256) {
*stackp++ = tab_suffixof(code);
code = tab_prefixof(code);
}
*stackp++ = finchar = tab_suffixof(code);

/* And put them out in forward order. */
middle: do {
if (count-- == 0)
return (num);
*bp++ = *--stackp;
} while (stackp > de_stack);

/* Generate the new entry. */
if ((code = free_ent) < maxmaxcode && oldcode != -1) {
tab_prefixof(code) = (u_short) oldcode;
tab_suffixof(code) = finchar;
free_ent = code + 1;
}

/* Remember previous code. */
oldcode = incode;
}
state = S_EOF;
eof: return (num - count);
}

/*-
* Read one code from the standard input. If EOF, return -1.
* Inputs:
* stdin
* Outputs:
* code or -1 is returned.
*/
static code_int
getcode(struct s_zstate *zs)
{
code_int gcode;
int r_off, bits;
char_type *bp;

bp = gbuf;
if (clear_flg > 0 || roffset >= size || free_ent > maxcode) {
/*
* If the next entry will be too big for the current gcode
* size, then we must increase the size. This implies reading
* a new buffer full, too.
*/
if (free_ent > maxcode) {
n_bits++;
if (n_bits == maxbits) /* Won't get any bigger now. */
maxcode = maxmaxcode;
else
maxcode = MAXCODE(n_bits);
}
if (clear_flg > 0) {
maxcode = MAXCODE(n_bits = INIT_BITS);
clear_flg = 0;
}
size = fread(gbuf, 1, n_bits, fp);
if (size <= 0) /* End of file. */
return (-1);
roffset = 0;
/* Round size down to integral number of codes. */
size = (size << 3) - (n_bits - 1);
}
r_off = roffset;
bits = n_bits;

/* Get to the first byte. */
bp += (r_off >> 3);
r_off &= 7;

/* Get first part (low order bits). */
gcode = (*bp++ >> r_off);
bits -= (8 - r_off);
r_off = 8 - r_off; /* Now, roffset into gcode word. */

/* Get any 8 bit parts in the middle (<=1 for up to 16 bits). */
if (bits >= 8) {
gcode |= *bp++ << r_off;
r_off += 8;
bits -= 8;
}

/* High order bits. */
gcode |= (*bp & rmask[bits]) << r_off;
roffset += n_bits;

return (gcode);
}

static int
cl_block(struct s_zstate *zs) /* Table clear for block compress. */
{
long rat;

checkpoint = in_count + CHECK_GAP;

if (in_count > 0x007fffff) { /* Shift will overflow. */
rat = bytes_out >> 8;
if (rat == 0) /* Don't divide by zero. */
rat = 0x7fffffff;
else
rat = in_count / rat;
} else
rat = (in_count << 8) / bytes_out; /* 8 fractional bits. */
if (rat > ratio)
ratio = rat;
else {
ratio = 0;
memset(htab, 0xff, hsize * sizeof(count_int));
free_ent = FIRST;
clear_flg = 1;
if (output(zs, (code_int) CLEAR) == -1)
return (-1);
}
return (0);
}

FILE *
zopen(const char *fname, const char *mode, int bits)
{
struct s_zstate *zs;

if ((mode[0] != 'r' && mode[0] != 'w') || mode[1] != '\0' ||
bits < 0 || bits > BITS) {
errno = EINVAL;
return (NULL);
}

if ((zs = calloc(1, sizeof(struct s_zstate))) == NULL)
return (NULL);

maxbits = bits ? bits : BITS; /* User settable max # bits/code. */
maxmaxcode = 1 << maxbits; /* Should NEVER generate this code. */
hsize = HSIZE; /* For dynamic table sizing. */
free_ent = 0; /* First unused entry. */
block_compress = BLOCK_MASK;
clear_flg = 0;
ratio = 0;
checkpoint = CHECK_GAP;
in_count = 1; /* Length of input. */
out_count = 0; /* # of codes output (for debugging). */
state = S_START;
roffset = 0;
size = 0;

/*
* Layering compress on top of stdio in order to provide buffering,
* and ensure that reads and write work with the data specified.
*/
if ((fp = fopen(fname, mode)) == NULL) {
free(zs);
return (NULL);
}
switch (*mode) {
case 'r':
zmode = 'r';
return (funopen(zs, zread, NULL, NULL, zclose));
case 'w':
zmode = 'w';
return (funopen(zs, NULL, zwrite, NULL, zclose));
}
/* NOTREACHED */
return (NULL);
}