/*      $OpenBSD: zopen.c,v 1.22 2017/05/29 14:41:16 fcambus Exp $      */
/*      $NetBSD: zopen.c,v 1.5 1995/03/26 09:44:53 glass 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.
 *
 *      From: @(#)zopen.c       8.1 (Berkeley) 6/27/93
 */

/*-
 * 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/stat.h>

#include <ctype.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include "compress.h"

#define MINIMUM(a, b)   (((a) < (b)) ? (a) : (b))

#define BITS            16              /* Default bits. */
#define HSIZE           69001           /* 95% occupancy */
#define ZBUFSIZ         8192            /* I/O buffer size */

/* 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;

static const u_char z_magic[] =
        {'\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 {
        int zs_fd;                      /* File stream for I/O */
        char zs_mode;                   /* r or w */
        enum {
                S_START, S_MAGIC, 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;
        long zs_in_count;               /* Length of input. */
        long zs_bytes_out;              /* Length of output. */
        long zs_out_count;              /* # of codes output (for debugging).*/
        u_char zs_buf[ZBUFSIZ];         /* I/O buffer */
        u_char *zs_bp;                  /* Current I/O window in the zs_buf */
        int zs_offset;                  /* Number of bits in the zs_buf */
        union {
                struct {
                        long zs_fcode;
                        code_int zs_ent;
                        code_int zs_hsize_reg;
                        int zs_hshift;
                } w;                    /* Write parameters */
                struct {
                        u_char *zs_stackp, *zs_ebp;
                        int zs_finchar;
                        code_int zs_code, zs_oldcode, zs_incode;
                        int zs_size;
                } r;                    /* Read parameters */
        } u;
};

/* Definitions to retain old variable names */
#define zs_fcode        u.w.zs_fcode
#define zs_ent          u.w.zs_ent
#define zs_hsize_reg    u.w.zs_hsize_reg
#define zs_hshift       u.w.zs_hshift
#define zs_stackp       u.r.zs_stackp
#define zs_finchar      u.r.zs_finchar
#define zs_code         u.r.zs_code
#define zs_oldcode      u.r.zs_oldcode
#define zs_incode       u.r.zs_incode
#define zs_size         u.r.zs_size
#define zs_ebp          u.r.zs_ebp

/*
 * 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)       zs->zs_htab[i]
#define codetabof(i)    zs->zs_codetab[i]

#define tab_prefixof(i) codetabof(i)
#define tab_suffixof(i) ((u_char *)(zs->zs_htab))[i]
#define de_stack        ((u_char *)&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);

/*-
 * 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.
 */
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;

        zs = cookie;
        count = num;
        bp = (u_char *)wbp;
        switch (zs->zs_state) {
        case S_MAGIC:
                return -1;
        case S_EOF:
                return 0;
        case S_START:
                zs->zs_state = S_MIDDLE;

                zs->zs_maxmaxcode = 1L << zs->zs_maxbits;
                if (write(zs->zs_fd, z_magic, sizeof(z_magic)) !=
                    sizeof(z_magic))
                        return (-1);
                tmp = (u_char)(zs->zs_maxbits | zs->zs_block_compress);
                if (write(zs->zs_fd, &tmp, sizeof(tmp)) != sizeof(tmp))
                        return (-1);

                zs->zs_bp = zs->zs_buf;
                zs->zs_offset = 0;
                zs->zs_bytes_out = 3;   /* Includes 3-byte header mojo. */
                zs->zs_out_count = 0;
                zs->zs_clear_flg = 0;
                zs->zs_ratio = 0;
                zs->zs_in_count = 1;
                zs->zs_checkpoint = CHECK_GAP;
                zs->zs_maxcode = MAXCODE(zs->zs_n_bits = INIT_BITS);
                zs->zs_free_ent = ((zs->zs_block_compress) ? FIRST : 256);

                zs->zs_ent = *bp++;
                --count;

                zs->zs_hshift = 0;
                for (zs->zs_fcode = (long)zs->zs_hsize; zs->zs_fcode < 65536L;
                    zs->zs_fcode *= 2L)
                        zs->zs_hshift++;
                /* Set hash code range bound. */
                zs->zs_hshift = 8 - zs->zs_hshift;

                zs->zs_hsize_reg = zs->zs_hsize;
                /* Clear hash table. */
                cl_hash(zs, (count_int)zs->zs_hsize_reg);

        case S_MIDDLE:
                for (i = 0; count-- > 0;) {
                        c = *bp++;
                        zs->zs_in_count++;
                        zs->zs_fcode = (long)(((long)c << zs->zs_maxbits) +
                            zs->zs_ent);
                        /* Xor hashing. */
                        i = ((c << zs->zs_hshift) ^ zs->zs_ent);

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

                        if (htabof(i) == zs->zs_fcode) {
                                zs->zs_ent = codetabof(i);
                                continue;
                        }
                        if ((long)htabof(i) >= 0)
                                goto probe;
nomatch:                if (output(zs, (code_int) zs->zs_ent) == -1)
                                return (-1);
                        zs->zs_out_count++;
                        zs->zs_ent = c;
                        if (zs->zs_free_ent < zs->zs_maxmaxcode) {
                                /* code -> hashtable */
                                codetabof(i) = zs->zs_free_ent++;
                                htabof(i) = zs->zs_fcode;
                        } else if ((count_int)zs->zs_in_count >=
                            zs->zs_checkpoint && zs->zs_block_compress) {
                                if (cl_block(zs) == -1)
                                        return (-1);
                        }
                }
        }
        return (num);
}

int
z_close(void *cookie, struct z_info *info, const char *name, struct stat *sb)
{
        struct s_zstate *zs;
        int rval;

        zs = cookie;
        if (zs->zs_mode == 'w') {               /* Put out the final code. */
                if (output(zs, (code_int) zs->zs_ent) == -1) {
                        (void)close(zs->zs_fd);
                        free(zs);
                        return (-1);
                }
                zs->zs_out_count++;
                if (output(zs, (code_int) - 1) == -1) {
                        (void)close(zs->zs_fd);
                        free(zs);
                        return (-1);
                }
        }

        if (info != NULL) {
                info->mtime = 0;
                info->crc = (u_int32_t)-1;
                info->hlen = 0;
                info->total_in = (off_t)zs->zs_in_count;
                info->total_out = (off_t)zs->zs_bytes_out;
        }

#ifndef SAVECORE
        setfile(name, zs->zs_fd, sb);
#endif
        rval = close(zs->zs_fd);
        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 const u_char lmask[9] =
        {0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80, 0x00};
static const u_char rmask[9] =
        {0x00, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f, 0xff};

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

        if (ocode >= 0) {
                int r_off;
                u_char *bp;

                /* Get to the first byte. */
                bp = zs->zs_bp + (zs->zs_offset >> 3);
                r_off = zs->zs_offset & 7;
                bits = zs->zs_n_bits;

                /*
                 * 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;
                zs->zs_offset += zs->zs_n_bits;
                if (zs->zs_offset == (zs->zs_n_bits << 3)) {
                        zs->zs_bp += zs->zs_n_bits;
                        zs->zs_offset = 0;
                }
                /*
                 * If the next entry is going to be too big for the ocode size,
                 * then increase it, if possible.
                 */
                if (zs->zs_free_ent > zs->zs_maxcode ||
                    (zs->zs_clear_flg > 0)) {
                        /*
                         * Write the whole buffer, because the input side won't
                         * discover the size increase until after it has read it
                         */
                        if (zs->zs_offset > 0) {
                                zs->zs_bp += zs->zs_n_bits;
                                zs->zs_offset = 0;
                        }

                        if (zs->zs_clear_flg) {
                                zs->zs_maxcode =
                                        MAXCODE(zs->zs_n_bits = INIT_BITS);
                                zs->zs_clear_flg = 0;
                        } else {
                                zs->zs_n_bits++;
                                if (zs->zs_n_bits == zs->zs_maxbits)
                                        zs->zs_maxcode = zs->zs_maxmaxcode;
                                else
                                        zs->zs_maxcode =
                                            MAXCODE(zs->zs_n_bits);
                        }
                }

                if (zs->zs_bp + zs->zs_n_bits > &zs->zs_buf[ZBUFSIZ]) {
                        bits = zs->zs_bp - zs->zs_buf;
                        if (write(zs->zs_fd, zs->zs_buf, bits) != bits)
                                return (-1);
                        zs->zs_bytes_out += bits;
                        if (zs->zs_offset > 0)
                                fprintf (stderr, "zs_offset != 0\n");
                        zs->zs_bp = zs->zs_buf;
                }
        } else {
                /* At EOF, write the rest of the buffer. */
                if (zs->zs_offset > 0)
                        zs->zs_bp += (zs->zs_offset + 7) / 8;
                if (zs->zs_bp > zs->zs_buf) {
                        bits = zs->zs_bp - zs->zs_buf;
                        if (write(zs->zs_fd, zs->zs_buf, bits) != bits)
                                return (-1);
                        zs->zs_bytes_out += bits;
                }
                zs->zs_offset = 0;
                zs->zs_bp = zs->zs_buf;
        }
        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.
 */
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 (zs->zs_state) {
        case S_START:
                zs->zs_state = S_MIDDLE;
                zs->zs_bp = zs->zs_buf;
                header[0] = header[1] = header[2] = '\0';
                read(zs->zs_fd, header, sizeof(header));
                break;
        case S_MAGIC:
                zs->zs_state = S_MIDDLE;
                zs->zs_bp = zs->zs_buf;
                header[0] = z_magic[0];
                header[1] = z_magic[1];
                header[2] = '\0';
                read(zs->zs_fd, &header[2], 1);
                break;
        case S_MIDDLE:
                goto middle;
        case S_EOF:
                goto eof;
        }

        /* Check the magic number */
        if (header[0] != z_magic[0] || header[1] != z_magic[1]) {
                errno = EFTYPE;
                return (-1);
        }
        zs->zs_maxbits = header[2];     /* Set -b from file. */
        zs->zs_in_count += sizeof(header);
        zs->zs_block_compress = zs->zs_maxbits & BLOCK_MASK;
        zs->zs_maxbits &= BIT_MASK;
        zs->zs_maxmaxcode = 1L << zs->zs_maxbits;
        if (zs->zs_maxbits > BITS) {
                errno = EFTYPE;
                return (-1);
        }
        /* As above, initialize the first 256 entries in the table. */
        zs->zs_maxcode = MAXCODE(zs->zs_n_bits = INIT_BITS);
        for (zs->zs_code = 255; zs->zs_code >= 0; zs->zs_code--) {
                tab_prefixof(zs->zs_code) = 0;
                tab_suffixof(zs->zs_code) = (u_char) zs->zs_code;
        }
        zs->zs_free_ent = zs->zs_block_compress ? FIRST : 256;

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

        /* First code must be 8 bits = char. */
        *bp++ = (u_char)zs->zs_finchar;
        count--;
        zs->zs_stackp = de_stack;

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

                if ((zs->zs_code == CLEAR) && zs->zs_block_compress) {
                        for (zs->zs_code = 255; zs->zs_code >= 0;
                            zs->zs_code--)
                                tab_prefixof(zs->zs_code) = 0;
                        zs->zs_clear_flg = 1;
                        zs->zs_free_ent = FIRST - 1;
                        if ((zs->zs_code = getcode(zs)) == -1)  /* O, untimely death! */
                                break;
                }
                zs->zs_incode = zs->zs_code;

                /* Special case for KwKwK string. */
                if (zs->zs_code >= zs->zs_free_ent) {
                        *zs->zs_stackp++ = zs->zs_finchar;
                        zs->zs_code = zs->zs_oldcode;
                }

                /* Generate output characters in reverse order. */
                while (zs->zs_code >= 256) {
                        /*
                         * Bad input file may cause zs_stackp to overflow
                         * zs_htab; check here and abort decompression,
                         * that's better than dumping core.
                         */
                        if (zs->zs_stackp >= (u_char *)&zs->zs_htab[HSIZE]) {
                                errno = EINVAL;
                                return (-1);
                        }
                        *zs->zs_stackp++ = tab_suffixof(zs->zs_code);
                        zs->zs_code = tab_prefixof(zs->zs_code);
                }
                *zs->zs_stackp++ = zs->zs_finchar = tab_suffixof(zs->zs_code);

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

                /* Generate the new entry. */
                if ((zs->zs_code = zs->zs_free_ent) < zs->zs_maxmaxcode) {
                        tab_prefixof(zs->zs_code) = (u_short) zs->zs_oldcode;
                        tab_suffixof(zs->zs_code) = zs->zs_finchar;
                        zs->zs_free_ent = zs->zs_code + 1;
                }

                /* Remember previous code. */
                zs->zs_oldcode = zs->zs_incode;
        }
        zs->zs_state = S_EOF;
        zs->zs_bytes_out += num - count;
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;
        u_char *bp;

        if (zs->zs_clear_flg > 0 || zs->zs_offset >= zs->zs_size ||
            zs->zs_free_ent > zs->zs_maxcode) {

                zs->zs_bp += zs->zs_n_bits;
                /*
                 * 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 (zs->zs_free_ent > zs->zs_maxcode) {
                        zs->zs_n_bits++;
                        if (zs->zs_n_bits == zs->zs_maxbits) {
                                /* Won't get any bigger now. */
                                zs->zs_maxcode = zs->zs_maxmaxcode;
                        } else
                                zs->zs_maxcode = MAXCODE(zs->zs_n_bits);
                }
                if (zs->zs_clear_flg > 0) {
                        zs->zs_maxcode = MAXCODE(zs->zs_n_bits = INIT_BITS);
                        zs->zs_clear_flg = 0;
                }

                /* fill the buffer up to the neck */
                if (zs->zs_bp + zs->zs_n_bits > zs->zs_ebp) {
                        for (bp = zs->zs_buf; zs->zs_bp < zs->zs_ebp;
                                *bp++ = *zs->zs_bp++);
                        if ((bits = read(zs->zs_fd, bp, ZBUFSIZ -
                            (bp - zs->zs_buf))) < 0)
                                return -1;
                        zs->zs_in_count += bits;
                        zs->zs_bp = zs->zs_buf;
                        zs->zs_ebp = bp + bits;
                }
                zs->zs_offset = 0;
                zs->zs_size = MINIMUM(zs->zs_n_bits, zs->zs_ebp - zs->zs_bp);
                if (zs->zs_size == 0)
                        return -1;
                /* Round size down to integral number of codes. */
                zs->zs_size = (zs->zs_size << 3) - (zs->zs_n_bits - 1);
        }

        bp = zs->zs_bp;
        r_off = zs->zs_offset;
        bits = zs->zs_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;
        zs->zs_offset += zs->zs_n_bits;

        return (gcode);
}

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

        zs->zs_checkpoint = zs->zs_in_count + CHECK_GAP;

        if (zs->zs_in_count > 0x007fffff) {     /* Shift will overflow. */
                rat = zs->zs_bytes_out >> 8;
                if (rat == 0)           /* Don't divide by zero. */
                        rat = 0x7fffffff;
                else
                        rat = zs->zs_in_count / rat;
        } else {
                /* 8 fractional bits. */
                rat = (zs->zs_in_count << 8) / zs->zs_bytes_out;
        }
        if (rat > zs->zs_ratio)
                zs->zs_ratio = rat;
        else {
                zs->zs_ratio = 0;
                cl_hash(zs, (count_int) zs->zs_hsize);
                zs->zs_free_ent = FIRST;
                zs->zs_clear_flg = 1;
                if (output(zs, (code_int) CLEAR) == -1)
                        return (-1);
        }
        return (0);
}

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

        m1 = -1;
        htab_p = zs->zs_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;
}

void *
z_wopen(int fd, char *name, int bits, u_int32_t mtime)
{
        struct s_zstate *zs;

        if (bits < 0 || bits > BITS) {
                errno = EINVAL;
                return (NULL);
        }

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

        /* User settable max # bits/code. */
        zs->zs_maxbits = bits ? bits : BITS;
        /* Should NEVER generate this code. */
        zs->zs_maxmaxcode = 1 << zs->zs_maxbits;
        zs->zs_hsize = HSIZE;           /* For dynamic table sizing. */
        zs->zs_free_ent = 0;            /* First unused entry. */
        zs->zs_block_compress = BLOCK_MASK;
        zs->zs_clear_flg = 0;
        zs->zs_ratio = 0;
        zs->zs_checkpoint = CHECK_GAP;
        zs->zs_in_count = 0;            /* Length of input. */
        zs->zs_out_count = 0;           /* # of codes output (for debugging).*/
        zs->zs_state = S_START;
        zs->zs_offset = 0;
        zs->zs_size = 0;
        zs->zs_mode = 'w';
        zs->zs_bp = zs->zs_ebp = zs->zs_buf;

        zs->zs_fd = fd;
        return zs;
}

void *
z_ropen(int fd, char *name, int gotmagic)
{
        struct s_zstate *zs;

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

        /* User settable max # bits/code. */
        zs->zs_maxbits = BITS;
        /* Should NEVER generate this code. */
        zs->zs_maxmaxcode = 1 << zs->zs_maxbits;
        zs->zs_hsize = HSIZE;           /* For dynamic table sizing. */
        zs->zs_free_ent = 0;            /* First unused entry. */
        zs->zs_block_compress = BLOCK_MASK;
        zs->zs_clear_flg = 0;
        zs->zs_ratio = 0;
        zs->zs_checkpoint = CHECK_GAP;
        zs->zs_in_count = 0;            /* Length of input. */
        zs->zs_out_count = 0;           /* # of codes output (for debugging).*/
        zs->zs_state = gotmagic ? S_MAGIC : S_START;
        zs->zs_offset = 0;
        zs->zs_size = 0;
        zs->zs_mode = 'r';
        zs->zs_bp = zs->zs_ebp = zs->zs_buf;

        zs->zs_fd = fd;
        return zs;
}