/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * 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.
 */


#include <sys/cdefs.h>
/*-
 * 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 <dds@doc.ic.ac.uk>.
 *
 * 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 <ctype.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "zopen.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 */
        u_int zs_n_bits;                /* Number of bits/code. */
        u_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;
        u_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 void     cl_hash(struct s_zstate *, count_int);
static code_int getcode(struct s_zstate *);
static int      output(struct s_zstate *, code_int);
static int      zclose(void *);
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;
        cl_hash(zs, (count_int)hsize_reg);      /* Clear hash table. */

middle: for (i = 0; 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 r_off;
        u_int bits;
        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) != 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) != 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) != 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;

        finchar = oldcode = getcode(zs);
        if (oldcode == -1)      /* EOF already? */
                return (0);     /* Get out of here */

        /* First code must be 8 bits = char. */
        *bp++ = (u_char)finchar;
        count--;
        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. */
        if (bits > 0)
                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;
                cl_hash(zs, (count_int) hsize);
                free_ent = FIRST;
                clear_flg = 1;
                if (output(zs, (code_int) CLEAR) == -1)
                        return (-1);
        }
        return (0);
}

static void
cl_hash(struct s_zstate *zs, count_int cl_hsize)        /* Reset code table. */
{
        count_int *htab_p;
        long i, m1;

        m1 = -1;
        htab_p = htab + cl_hsize;
        i = cl_hsize - 16;
        do {                    /* Might use Sys V memset(3) here. */
                *(htab_p - 16) = m1;
                *(htab_p - 15) = m1;
                *(htab_p - 14) = m1;
                *(htab_p - 13) = m1;
                *(htab_p - 12) = m1;
                *(htab_p - 11) = m1;
                *(htab_p - 10) = m1;
                *(htab_p - 9) = m1;
                *(htab_p - 8) = m1;
                *(htab_p - 7) = m1;
                *(htab_p - 6) = m1;
                *(htab_p - 5) = m1;
                *(htab_p - 4) = m1;
                *(htab_p - 3) = m1;
                *(htab_p - 2) = m1;
                *(htab_p - 1) = m1;
                htab_p -= 16;
        } while ((i -= 16) >= 0);
        for (i += 16; i > 0; i--)
                *--htab_p = m1;
}

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 = 1L << 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);
}