source: MondoRescue/branches/2.2.2/mindi-busybox/coreutils/diff.c@ 1247

/* vi: set sw=4 ts=4: */
/*
 * Mini diff implementation for busybox, adapted from OpenBSD diff.
 *
 * Copyright (C) 2006 by Robert Sullivan <cogito.ergo.cogito@hotmail.com>
 * Copyright (c) 2003 Todd C. Miller <Todd.Miller@courtesan.com>
 *
 * Sponsored in part by the Defense Advanced Research Projects
 * Agency (DARPA) and Air Force Research Laboratory, Air Force
 * Materiel Command, USAF, under agreement number F39502-99-1-0512.
 *
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 */

#include <time.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <ctype.h>
#include <errno.h>
#include <signal.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <stddef.h>
#include <paths.h>
#include <dirent.h>
#include "busybox.h"

#define FSIZE_MAX 32768

/*
 * Output flags
 */
#define D_HEADER        1   /* Print a header/footer between files */
#define D_EMPTY1        2   /* Treat first file as empty (/dev/null) */
#define D_EMPTY2        4   /* Treat second file as empty (/dev/null) */

/*
 * Status values for print_status() and diffreg() return values
 * Guide:
 * D_SAME - files are the same
 * D_DIFFER - files differ
 * D_BINARY - binary files differ
 * D_COMMON - subdirectory common to both dirs
 * D_ONLY - file only exists in one dir
 * D_MISMATCH1 - path1 a dir, path2 a file
 * D_MISMATCH2 - path1 a file, path2 a dir
 * D_ERROR - error occurred
 * D_SKIPPED1 - skipped path1 as it is a special file
 * D_SKIPPED2 - skipped path2 as it is a special file
 */

#define D_SAME      0
#define D_DIFFER    (1<<0)
#define D_BINARY    (1<<1)
#define D_COMMON    (1<<2)
#define D_ONLY      (1<<3)
#define D_MISMATCH1 (1<<4)
#define D_MISMATCH2 (1<<5)
#define D_ERROR     (1<<6)
#define D_SKIPPED1  (1<<7)
#define D_SKIPPED2  (1<<8)

/* Command line options */
static unsigned long cmd_flags;

#define FLAG_a  (1<<0)
#define FLAG_b  (1<<1)
#define FLAG_d  (1<<2)
#define FLAG_i  (1<<3)
#define FLAG_L  (1<<4)
#define FLAG_N  (1<<5)
#define FLAG_q  (1<<6)
#define FLAG_r  (1<<7)
#define FLAG_s  (1<<8)
#define FLAG_S  (1<<9)
#define FLAG_t  (1<<10)
#define FLAG_T  (1<<11)
#define FLAG_U  (1<<12)
#define FLAG_w  (1<<13)

int context, status;
char *start, *label[2];
struct stat stb1, stb2;
char **dl;
int dl_count = 0;

struct cand {
    int x;
    int y;
    int pred;
};

struct line {
    int serial;
    int value;
} *file[2];

/*
 * The following struct is used to record change information
 * doing a "context" or "unified" diff.  (see routine "change" to
 * understand the highly mnemonic field names)
 */
struct context_vec {
    int a;              /* start line in old file */
    int b;              /* end line in old file */
    int c;              /* start line in new file */
    int d;              /* end line in new file */
};

static int *J;          /* will be overlaid on class */
static int *class;      /* will be overlaid on file[0] */
static int *klist;      /* will be overlaid on file[0] after class */
static int *member;     /* will be overlaid on file[1] */
static int clen;
static int len[2];
static int pref, suff;  /* length of prefix and suffix */
static int slen[2];
static int anychange;
static long *ixnew;     /* will be overlaid on file[1] */
static long *ixold;     /* will be overlaid on klist */
static struct cand *clist;  /* merely a free storage pot for candidates */
static int clistlen;    /* the length of clist */
static struct line *sfile[2];   /* shortened by pruning common prefix/suffix */
static struct context_vec *context_vec_start;
static struct context_vec *context_vec_end;
static struct context_vec *context_vec_ptr;

static void print_only(const char *path, size_t dirlen, const char *entry)
{
    if (dirlen > 1)
        dirlen--;
    printf("Only in %.*s: %s\n", (int) dirlen, path, entry);
}

static void print_status(int val, char *path1, char *path2, char *entry)
{
    const char *const _entry = entry ? entry : "";
    char *_path1 = entry ? concat_path_file(path1, _entry) : path1;
    char *_path2 = entry ? concat_path_file(path2, _entry) : path2;

    switch (val) {
    case D_ONLY:
        print_only(path1, strlen(path1), entry);
        break;
    case D_COMMON:
        printf("Common subdirectories: %s and %s\n", _path1, _path2);
        break;
    case D_BINARY:
        printf("Binary files %s and %s differ\n", _path1, _path2);
        break;
    case D_DIFFER:
        if (cmd_flags & FLAG_q)
            printf("Files %s and %s differ\n", _path1, _path2);
        break;
    case D_SAME:
        if (cmd_flags & FLAG_s)
            printf("Files %s and %s are identical\n", _path1, _path2);
        break;
    case D_MISMATCH1:
        printf("File %s is a directory while file %s is a regular file\n",
               _path1, _path2);
        break;
    case D_MISMATCH2:
        printf("File %s is a regular file while file %s is a directory\n",
               _path1, _path2);
        break;
    case D_SKIPPED1:
        printf("File %s is not a regular file or directory and was skipped\n",
               _path1);
        break;
    case D_SKIPPED2:
        printf("File %s is not a regular file or directory and was skipped\n",
               _path2);
        break;
    }
    if (entry) {
        free(_path1);
        free(_path2);
    }
}

/*
 * Hash function taken from Robert Sedgewick, Algorithms in C, 3d ed., p 578.
 */
static int readhash(FILE * f)
{
    int i, t, space;
    int sum;

    sum = 1;
    space = 0;
    if (!(cmd_flags & FLAG_b) && !(cmd_flags & FLAG_w)) {
        if (FLAG_i)
            for (i = 0; (t = getc(f)) != '\n'; i++) {
                if (t == EOF) {
                    if (i == 0)
                        return (0);
                    break;
                }
                sum = sum * 127 + t;
        } else
            for (i = 0; (t = getc(f)) != '\n'; i++) {
                if (t == EOF) {
                    if (i == 0)
                        return (0);
                    break;
                }
                sum = sum * 127 + t;
            }
    } else {
        for (i = 0;;) {
            switch (t = getc(f)) {
            case '\t':
            case '\r':
            case '\v':
            case '\f':
            case ' ':
                space++;
                continue;
            default:
                if (space && !(cmd_flags & FLAG_w)) {
                    i++;
                    space = 0;
                }
                sum = sum * 127 + t;
                i++;
                continue;
            case EOF:
                if (i == 0)
                    return (0);
                /* FALLTHROUGH */
            case '\n':
                break;
            }
            break;
        }
    }
    /*
     * There is a remote possibility that we end up with a zero sum.
     * Zero is used as an EOF marker, so return 1 instead.
     */
    return (sum == 0 ? 1 : sum);
}



/*
 * Check to see if the given files differ.
 * Returns 0 if they are the same, 1 if different, and -1 on error.
 */
static int files_differ(FILE * f1, FILE * f2, int flags)
{
    char buf1[BUFSIZ], buf2[BUFSIZ];
    size_t i, j;

    if ((flags & (D_EMPTY1 | D_EMPTY2)) || stb1.st_size != stb2.st_size ||
        (stb1.st_mode & S_IFMT) != (stb2.st_mode & S_IFMT))
        return (1);
    while (1) {
        i = fread(buf1, 1, sizeof(buf1), f1);
        j = fread(buf2, 1, sizeof(buf2), f2);
        if (i != j)
            return (1);
        if (i == 0 && j == 0) {
            if (ferror(f1) || ferror(f2))
                return (1);
            return (0);
        }
        if (memcmp(buf1, buf2, i) != 0)
            return (1);
    }
}

static void prepare(int i, FILE * fd, off_t filesize)
{
    struct line *p;
    int h;
    size_t j, sz;

    rewind(fd);

    sz = (filesize <= FSIZE_MAX ? filesize : FSIZE_MAX) / 25;
    if (sz < 100)
        sz = 100;

    p = xmalloc((sz + 3) * sizeof(struct line));
    for (j = 0; (h = readhash(fd));) {
        if (j == sz) {
            sz = sz * 3 / 2;
            p = xrealloc(p, (sz + 3) * sizeof(struct line));
        }
        p[++j].value = h;
    }
    len[i] = j;
    file[i] = p;
}

static void prune(void)
{
    int i, j;

    for (pref = 0; pref < len[0] && pref < len[1] &&
         file[0][pref + 1].value == file[1][pref + 1].value; pref++);
    for (suff = 0; suff < len[0] - pref && suff < len[1] - pref &&
         file[0][len[0] - suff].value == file[1][len[1] - suff].value;
         suff++);
    for (j = 0; j < 2; j++) {
        sfile[j] = file[j] + pref;
        slen[j] = len[j] - pref - suff;
        for (i = 0; i <= slen[j]; i++)
            sfile[j][i].serial = i;
    }
}

static void equiv(struct line *a, int n, struct line *b, int m, int *c)
{
    int i, j;

    i = j = 1;
    while (i <= n && j <= m) {
        if (a[i].value < b[j].value)
            a[i++].value = 0;
        else if (a[i].value == b[j].value)
            a[i++].value = j;
        else
            j++;
    }
    while (i <= n)
        a[i++].value = 0;
    b[m + 1].value = 0;
    j = 0;
    while (++j <= m) {
        c[j] = -b[j].serial;
        while (b[j + 1].value == b[j].value) {
            j++;
            c[j] = b[j].serial;
        }
    }
    c[j] = -1;
}

static int isqrt(int n)
{
    int y, x = 1;

    if (n == 0)
        return (0);

    do {
        y = x;
        x = n / x;
        x += y;
        x /= 2;
    } while ((x - y) > 1 || (x - y) < -1);

    return (x);
}

static int newcand(int x, int y, int pred)
{
    struct cand *q;

    if (clen == clistlen) {
        clistlen = clistlen * 11 / 10;
        clist = xrealloc(clist, clistlen * sizeof(struct cand));
    }
    q = clist + clen;
    q->x = x;
    q->y = y;
    q->pred = pred;
    return (clen++);
}


static int search(int *c, int k, int y)
{
    int i, j, l, t;

    if (clist[c[k]].y < y)  /* quick look for typical case */
        return (k + 1);
    i = 0;
    j = k + 1;
    while (1) {
        l = i + j;
        if ((l >>= 1) <= i)
            break;
        t = clist[c[l]].y;
        if (t > y)
            j = l;
        else if (t < y)
            i = l;
        else
            return (l);
    }
    return (l + 1);
}


static int stone(int *a, int n, int *b, int *c)
{
    int i, k, y, j, l;
    int oldc, tc, oldl;
    unsigned int numtries;

#if ENABLE_FEATURE_DIFF_MINIMAL
    const unsigned int bound =
        (cmd_flags & FLAG_d) ? UINT_MAX : MAX(256, isqrt(n));
#else
    const unsigned int bound = MAX(256, isqrt(n));
#endif
    k = 0;
    c[0] = newcand(0, 0, 0);
    for (i = 1; i <= n; i++) {
        j = a[i];
        if (j == 0)
            continue;
        y = -b[j];
        oldl = 0;
        oldc = c[0];
        numtries = 0;
        do {
            if (y <= clist[oldc].y)
                continue;
            l = search(c, k, y);
            if (l != oldl + 1)
                oldc = c[l - 1];
            if (l <= k) {
                if (clist[c[l]].y <= y)
                    continue;
                tc = c[l];
                c[l] = newcand(i, y, oldc);
                oldc = tc;
                oldl = l;
                numtries++;
            } else {
                c[l] = newcand(i, y, oldc);
                k++;
                break;
            }
        } while ((y = b[++j]) > 0 && numtries < bound);
    }
    return (k);
}

static void unravel(int p)
{
    struct cand *q;
    int i;

    for (i = 0; i <= len[0]; i++)
        J[i] = i <= pref ? i : i > len[0] - suff ? i + len[1] - len[0] : 0;
    for (q = clist + p; q->y != 0; q = clist + q->pred)
        J[q->x + pref] = q->y + pref;
}


static void unsort(struct line *f, int l, int *b)
{
    int *a, i;

    a = xmalloc((l + 1) * sizeof(int));
    for (i = 1; i <= l; i++)
        a[f[i].serial] = f[i].value;
    for (i = 1; i <= l; i++)
        b[i] = a[i];
    free(a);
}

static int skipline(FILE * f)
{
    int i, c;

    for (i = 1; (c = getc(f)) != '\n' && c != EOF; i++)
        continue;
    return (i);
}


/*
 * Check does double duty:
 *  1.  ferret out any fortuitous correspondences due
 *      to confounding by hashing (which result in "jackpot")
 *  2.  collect random access indexes to the two files
 */
static void check(FILE * f1, FILE * f2)
{
    int i, j, jackpot, c, d;
    long ctold, ctnew;

    rewind(f1);
    rewind(f2);
    j = 1;
    ixold[0] = ixnew[0] = 0;
    jackpot = 0;
    ctold = ctnew = 0;
    for (i = 1; i <= len[0]; i++) {
        if (J[i] == 0) {
            ixold[i] = ctold += skipline(f1);
            continue;
        }
        while (j < J[i]) {
            ixnew[j] = ctnew += skipline(f2);
            j++;
        }
        if ((cmd_flags & FLAG_b) || (cmd_flags & FLAG_w)
            || (cmd_flags & FLAG_i)) {
            while (1) {
                c = getc(f1);
                d = getc(f2);
                /*
                 * GNU diff ignores a missing newline
                 * in one file if bflag || wflag.
                 */
                if (((cmd_flags & FLAG_b) || (cmd_flags & FLAG_w)) &&
                    ((c == EOF && d == '\n') || (c == '\n' && d == EOF))) {
                    break;
                }
                ctold++;
                ctnew++;
                if ((cmd_flags & FLAG_b) && isspace(c) && isspace(d)) {
                    do {
                        if (c == '\n')
                            break;
                        ctold++;
                    } while (isspace(c = getc(f1)));
                    do {
                        if (d == '\n')
                            break;
                        ctnew++;
                    } while (isspace(d = getc(f2)));
                } else if (cmd_flags & FLAG_w) {
                    while (isspace(c) && c != '\n') {
                        c = getc(f1);
                        ctold++;
                    }
                    while (isspace(d) && d != '\n') {
                        d = getc(f2);
                        ctnew++;
                    }
                }
                if (c != d) {
                    jackpot++;
                    J[i] = 0;
                    if (c != '\n' && c != EOF)
                        ctold += skipline(f1);
                    if (d != '\n' && c != EOF)
                        ctnew += skipline(f2);
                    break;
                }
                if (c == '\n' || c == EOF)
                    break;
            }
        } else {
            while (1) {
                ctold++;
                ctnew++;
                if ((c = getc(f1)) != (d = getc(f2))) {
                    J[i] = 0;
                    if (c != '\n' && c != EOF)
                        ctold += skipline(f1);
                    if (d != '\n' && c != EOF)
                        ctnew += skipline(f2);
                    break;
                }
                if (c == '\n' || c == EOF)
                    break;
            }
        }
        ixold[i] = ctold;
        ixnew[j] = ctnew;
        j++;
    }
    for (; j <= len[1]; j++)
        ixnew[j] = ctnew += skipline(f2);
}

/* shellsort CACM #201 */
static void sort(struct line *a, int n)
{
    struct line *ai, *aim, w;
    int j, m = 0, k;

    if (n == 0)
        return;
    for (j = 1; j <= n; j *= 2)
        m = 2 * j - 1;
    for (m /= 2; m != 0; m /= 2) {
        k = n - m;
        for (j = 1; j <= k; j++) {
            for (ai = &a[j]; ai > a; ai -= m) {
                aim = &ai[m];
                if (aim < ai)
                    break;  /* wraparound */
                if (aim->value > ai[0].value ||
                    (aim->value == ai[0].value && aim->serial > ai[0].serial))
                    break;
                w.value = ai[0].value;
                ai[0].value = aim->value;
                aim->value = w.value;
                w.serial = ai[0].serial;
                ai[0].serial = aim->serial;
                aim->serial = w.serial;
            }
        }
    }
}


static void uni_range(int a, int b)
{
    if (a < b)
        printf("%d,%d", a, b - a + 1);
    else if (a == b)
        printf("%d", b);
    else
        printf("%d,0", b);
}

static int fetch(long *f, int a, int b, FILE * lb, int ch)
{
    int i, j, c, lastc, col, nc;

    if (a > b)
        return (0);
    for (i = a; i <= b; i++) {
        fseek(lb, f[i - 1], SEEK_SET);
        nc = f[i] - f[i - 1];
        if (ch != '\0') {
            putchar(ch);
            if (cmd_flags & FLAG_T)
                putchar('\t');
        }
        col = 0;
        for (j = 0, lastc = '\0'; j < nc; j++, lastc = c) {
            if ((c = getc(lb)) == EOF) {
                puts("\n\\ No newline at end of file");
                return (0);
            }
            if (c == '\t' && (cmd_flags & FLAG_t)) {
                do {
                    putchar(' ');
                } while (++col & 7);
            } else {
                putchar(c);
                col++;
            }
        }
    }
    return (0);
}

static int asciifile(FILE * f)
{
#if ENABLE_FEATURE_DIFF_BINARY
    unsigned char buf[BUFSIZ];
    int i, cnt;
#endif

    if ((cmd_flags & FLAG_a) || f == NULL)
        return (1);

#if ENABLE_FEATURE_DIFF_BINARY
    rewind(f);
    cnt = fread(buf, 1, sizeof(buf), f);
    for (i = 0; i < cnt; i++) {
        if (!isprint(buf[i]) && !isspace(buf[i])) {
            return (0);
        }
    }
#endif
    return (1);
}

/* dump accumulated "unified" diff changes */
static void dump_unified_vec(FILE * f1, FILE * f2)
{
    struct context_vec *cvp = context_vec_start;
    int lowa, upb, lowc, upd;
    int a, b, c, d;
    char ch;

    if (context_vec_start > context_vec_ptr)
        return;

    b = d = 0;          /* gcc */
    lowa = MAX(1, cvp->a - context);
    upb = MIN(len[0], context_vec_ptr->b + context);
    lowc = MAX(1, cvp->c - context);
    upd = MIN(len[1], context_vec_ptr->d + context);

    fputs("@@ -", stdout);
    uni_range(lowa, upb);
    fputs(" +", stdout);
    uni_range(lowc, upd);
    fputs(" @@", stdout);
    putchar('\n');

    /*
     * Output changes in "unified" diff format--the old and new lines
     * are printed together.
     */
    for (; cvp <= context_vec_ptr; cvp++) {
        a = cvp->a;
        b = cvp->b;
        c = cvp->c;
        d = cvp->d;

        /*
         * c: both new and old changes
         * d: only changes in the old file
         * a: only changes in the new file
         */
        if (a <= b && c <= d)
            ch = 'c';
        else
            ch = (a <= b) ? 'd' : 'a';
#if 0
        switch (ch) {
        case 'c':
            fetch(ixold, lowa, a - 1, f1, ' ');
            fetch(ixold, a, b, f1, '-');
            fetch(ixnew, c, d, f2, '+');
            break;
        case 'd':
            fetch(ixold, lowa, a - 1, f1, ' ');
            fetch(ixold, a, b, f1, '-');
            break;
        case 'a':
            fetch(ixnew, lowc, c - 1, f2, ' ');
            fetch(ixnew, c, d, f2, '+');
            break;
        }
#else
        if (ch == 'c' || ch == 'd') {
            fetch(ixold, lowa, a - 1, f1, ' ');
            fetch(ixold, a, b, f1, '-');
        }
        if (ch == 'a')
            fetch(ixnew, lowc, c - 1, f2, ' ');
        if (ch == 'c' || ch == 'a')
            fetch(ixnew, c, d, f2, '+');
#endif
        lowa = b + 1;
        lowc = d + 1;
    }
    fetch(ixnew, d + 1, upd, f2, ' ');

    context_vec_ptr = context_vec_start - 1;
}


static void print_header(const char *file1, const char *file2)
{
    if (label[0] != NULL)
        printf("%s %s\n", "---", label[0]);
    else
        printf("%s %s\t%s", "---", file1, ctime(&stb1.st_mtime));
    if (label[1] != NULL)
        printf("%s %s\n", "+++", label[1]);
    else
        printf("%s %s\t%s", "+++", file2, ctime(&stb2.st_mtime));
}



/*
 * Indicate that there is a difference between lines a and b of the from file
 * to get to lines c to d of the to file.  If a is greater then b then there
 * are no lines in the from file involved and this means that there were
 * lines appended (beginning at b).  If c is greater than d then there are
 * lines missing from the to file.
 */
static void change(char *file1, FILE * f1, char *file2, FILE * f2, int a,
                   int b, int c, int d)
{
    static size_t max_context = 64;

    if (a > b && c > d)
        return;
    if (cmd_flags & FLAG_q)
        return;

    /*
     * Allocate change records as needed.
     */
    if (context_vec_ptr == context_vec_end - 1) {
        ptrdiff_t offset = context_vec_ptr - context_vec_start;

        max_context <<= 1;
        context_vec_start = xrealloc(context_vec_start,
                                     max_context *
                                     sizeof(struct context_vec));
        context_vec_end = context_vec_start + max_context;
        context_vec_ptr = context_vec_start + offset;
    }
    if (anychange == 0) {
        /*
         * Print the context/unidiff header first time through.
         */
        print_header(file1, file2);
        anychange = 1;
    } else if (a > context_vec_ptr->b + (2 * context) + 1 &&
               c > context_vec_ptr->d + (2 * context) + 1) {
        /*
         * If this change is more than 'context' lines from the
         * previous change, dump the record and reset it.
         */
        dump_unified_vec(f1, f2);
    }
    context_vec_ptr++;
    context_vec_ptr->a = a;
    context_vec_ptr->b = b;
    context_vec_ptr->c = c;
    context_vec_ptr->d = d;
    return;

}


static void output(char *file1, FILE * f1, char *file2, FILE * f2)
{

    /* Note that j0 and j1 can't be used as they are defined in math.h.
     * This also allows the rather amusing variable 'j00'... */
    int m, i0, i1, j00, j01;

    rewind(f1);
    rewind(f2);
    m = len[0];
    J[0] = 0;
    J[m + 1] = len[1] + 1;
    for (i0 = 1; i0 <= m; i0 = i1 + 1) {
        while (i0 <= m && J[i0] == J[i0 - 1] + 1)
            i0++;
        j00 = J[i0 - 1] + 1;
        i1 = i0 - 1;
        while (i1 < m && J[i1 + 1] == 0)
            i1++;
        j01 = J[i1 + 1] - 1;
        J[i1] = j01;
        change(file1, f1, file2, f2, i0, i1, j00, j01);
    }
    if (m == 0) {
        change(file1, f1, file2, f2, 1, 0, 1, len[1]);
    }
    if (anychange != 0) {
        dump_unified_vec(f1, f2);
    }
}

/*
 *      The following code uses an algorithm due to Harold Stone, 
 *      which finds a pair of longest identical subsequences in 
 *      the two files.
 *
 *      The major goal is to generate the match vector J.
 *      J[i] is the index of the line in file1 corresponding
 *      to line i file0. J[i] = 0 if there is no
 *      such line in file1.
 *
 *      Lines are hashed so as to work in core. All potential
 *      matches are located by sorting the lines of each file
 *      on the hash (called ``value''). In particular, this
 *      collects the equivalence classes in file1 together.
 *      Subroutine equiv replaces the value of each line in
 *      file0 by the index of the first element of its
 *      matching equivalence in (the reordered) file1.
 *      To save space equiv squeezes file1 into a single
 *      array member in which the equivalence classes
 *      are simply concatenated, except that their first
 *      members are flagged by changing sign.
 *
 *      Next the indices that point into member are unsorted into
 *      array class according to the original order of file0.
 *
 *      The cleverness lies in routine stone. This marches
 *      through the lines of file0, developing a vector klist
 *      of "k-candidates". At step i a k-candidate is a matched
 *      pair of lines x,y (x in file0 y in file1) such that
 *      there is a common subsequence of length k
 *      between the first i lines of file0 and the first y
 *      lines of file1, but there is no such subsequence for
 *      any smaller y. x is the earliest possible mate to y
 *      that occurs in such a subsequence.
 *
 *      Whenever any of the members of the equivalence class of
 *      lines in file1 matable to a line in file0 has serial number
 *      less than the y of some k-candidate, that k-candidate
 *      with the smallest such y is replaced. The new
 *      k-candidate is chained (via pred) to the current
 *      k-1 candidate so that the actual subsequence can
 *      be recovered. When a member has serial number greater
 *      that the y of all k-candidates, the klist is extended.
 *      At the end, the longest subsequence is pulled out
 *      and placed in the array J by unravel
 *
 *      With J in hand, the matches there recorded are
 *      checked against reality to assure that no spurious
 *      matches have crept in due to hashing. If they have,
 *      they are broken, and "jackpot" is recorded--a harmless
 *      matter except that a true match for a spuriously
 *      mated line may now be unnecessarily reported as a change.
 *
 *      Much of the complexity of the program comes simply
 *      from trying to minimize core utilization and
 *      maximize the range of doable problems by dynamically
 *      allocating what is needed and reusing what is not.
 *      The core requirements for problems larger than somewhat
 *      are (in words) 2*length(file0) + length(file1) +
 *      3*(number of k-candidates installed),  typically about
 *      6n words for files of length n.
 */

static int diffreg(char *ofile1, char *ofile2, int flags)
{
    char *file1 = ofile1;
    char *file2 = ofile2;
    FILE *f1 = NULL;
    FILE *f2 = NULL;
    int rval = D_SAME;
    int i;

    anychange = 0;
    context_vec_ptr = context_vec_start - 1;

    if (S_ISDIR(stb1.st_mode) != S_ISDIR(stb2.st_mode))
        return (S_ISDIR(stb1.st_mode) ? D_MISMATCH1 : D_MISMATCH2);
    if (strcmp(file1, "-") == 0 && strcmp(file2, "-") == 0)
        goto closem;

    if (flags & D_EMPTY1)
        f1 = bb_xfopen(bb_dev_null, "r");
    else {
        if (strcmp(file1, "-") == 0)
            f1 = stdin;
        else
            f1 = bb_xfopen(file1, "r");
    }

    if (flags & D_EMPTY2)
        f2 = bb_xfopen(bb_dev_null, "r");
    else {
        if (strcmp(file2, "-") == 0)
            f2 = stdin;
        else
            f2 = bb_xfopen(file2, "r");
    }

    if ((i = files_differ(f1, f2, flags)) == 0)
        goto closem;
    else if (i != 1) {  /* 1 == ok */
        /* error */
        status |= 2;
        goto closem;
    }

    if (!asciifile(f1) || !asciifile(f2)) {
        rval = D_BINARY;
        status |= 1;
        goto closem;
    }

    prepare(0, f1, stb1.st_size);
    prepare(1, f2, stb2.st_size);
    prune();
    sort(sfile[0], slen[0]);
    sort(sfile[1], slen[1]);

    member = (int *) file[1];
    equiv(sfile[0], slen[0], sfile[1], slen[1], member);
    member = xrealloc(member, (slen[1] + 2) * sizeof(int));

    class = (int *) file[0];
    unsort(sfile[0], slen[0], class);
    class = xrealloc(class, (slen[0] + 2) * sizeof(int));

    klist = xmalloc((slen[0] + 2) * sizeof(int));
    clen = 0;
    clistlen = 100;
    clist = xmalloc(clistlen * sizeof(struct cand));
    i = stone(class, slen[0], member, klist);
    free(member);
    free(class);

    J = xrealloc(J, (len[0] + 2) * sizeof(int));
    unravel(klist[i]);
    free(clist);
    free(klist);

    ixold = xrealloc(ixold, (len[0] + 2) * sizeof(long));
    ixnew = xrealloc(ixnew, (len[1] + 2) * sizeof(long));
    check(f1, f2);
    output(file1, f1, file2, f2);

  closem:
    if (anychange) {
        status |= 1;
        if (rval == D_SAME)
            rval = D_DIFFER;
    }
    if (f1 != NULL)
        fclose(f1);
    if (f2 != NULL)
        fclose(f2);
    if (file1 != ofile1)
        free(file1);
    if (file2 != ofile2)
        free(file2);
    return (rval);
}

#if ENABLE_FEATURE_DIFF_DIR
static void do_diff(char *dir1, char *path1, char *dir2, char *path2)
{

    int flags = D_HEADER;
    int val;

    char *fullpath1 = bb_xasprintf("%s/%s", dir1, path1);
    char *fullpath2 = bb_xasprintf("%s/%s", dir2, path2);

    if (stat(fullpath1, &stb1) != 0) {
        flags |= D_EMPTY1;
        memset(&stb1, 0, sizeof(stb1));
        fullpath1 = bb_xasprintf("%s/%s", dir1, path2);
    }
    if (stat(fullpath2, &stb2) != 0) {
        flags |= D_EMPTY2;
        memset(&stb2, 0, sizeof(stb2));
        stb2.st_mode = stb1.st_mode;
        fullpath2 = bb_xasprintf("%s/%s", dir2, path1);
    }

    if (stb1.st_mode == 0)
        stb1.st_mode = stb2.st_mode;

    if (S_ISDIR(stb1.st_mode) && S_ISDIR(stb2.st_mode)) {
        printf("Common subdirectories: %s and %s\n", fullpath1, fullpath2);
        return;
    }

    if (!S_ISREG(stb1.st_mode) && !S_ISDIR(stb1.st_mode))
        val = D_SKIPPED1;
    else if (!S_ISREG(stb2.st_mode) && !S_ISDIR(stb2.st_mode))
        val = D_SKIPPED2;
    else
        val = diffreg(fullpath1, fullpath2, flags);

    print_status(val, fullpath1, fullpath2, NULL);
}
#endif

#if ENABLE_FEATURE_DIFF_DIR
static int dir_strcmp(const void *p1, const void *p2)
{
    return strcmp(*(char *const *) p1, *(char *const *) p2);
}

/* This function adds a filename to dl, the directory listing. */

static int add_to_dirlist(const char *filename,
                          struct stat ATTRIBUTE_UNUSED * sb, void *userdata)
{
    dl_count++;
    dl = xrealloc(dl, dl_count * sizeof(char *));
    dl[dl_count - 1] = bb_xstrdup(filename);
    if (cmd_flags & FLAG_r) {
        int *pp = (int *) userdata;
        int path_len = *pp + 1;

        dl[dl_count - 1] = &(dl[dl_count - 1])[path_len];
    }
    return TRUE;
}

/* This returns a sorted directory listing. */
static char **get_dir(char *path)
{

    int i;
    char **retval;

    /* If -r has been set, then the recursive_action function will be
     * used. Unfortunately, this outputs the root directory along with
     * the recursed paths, so use void *userdata to specify the string
     * length of the root directory. It can then be removed in
     * add_to_dirlist. */

    int path_len = strlen(path);
    void *userdata = &path_len;

    /* Reset dl_count - there's no need to free dl as bb_xrealloc does
     * the job nicely. */
    dl_count = 0;

    /* Now fill dl with a listing. */
    if (cmd_flags & FLAG_r)
        recursive_action(path, TRUE, TRUE, FALSE, add_to_dirlist, NULL,
                         userdata);
    else {
        DIR *dp;
        struct dirent *ep;

        dp = bb_opendir(path);
        while ((ep = readdir(dp))) {
            if ((!strcmp(ep->d_name, "..")) || (!strcmp(ep->d_name, ".")))
                continue;
            add_to_dirlist(ep->d_name, NULL, NULL);
        }
        closedir(dp);
    }

    /* Sort dl alphabetically. */
    qsort(dl, dl_count, sizeof(char *), dir_strcmp);

    /* Copy dl so that we can return it. */
    retval = xmalloc(dl_count * sizeof(char *));
    for (i = 0; i < dl_count; i++)
        retval[i] = bb_xstrdup(dl[i]);

    return retval;
}

static void diffdir(char *p1, char *p2)
{

    char **dirlist1, **dirlist2;
    char *dp1, *dp2;
    int dirlist1_count, dirlist2_count;
    int pos;

    /* Check for trailing slashes. */

    if (p1[strlen(p1) - 1] == '/')
        p1[strlen(p1) - 1] = '\0';
    if (p2[strlen(p2) - 1] == '/')
        p2[strlen(p2) - 1] = '\0';

    /* Get directory listings for p1 and p2. */

    dirlist1 = get_dir(p1);
    dirlist1_count = dl_count;
    dirlist1[dirlist1_count] = NULL;
    dirlist2 = get_dir(p2);
    dirlist2_count = dl_count;
    dirlist2[dirlist2_count] = NULL;

    /* If -S was set, find the starting point. */
    if (start) {
        while (*dirlist1 != NULL && strcmp(*dirlist1, start) < 0)
            dirlist1++;
        while (*dirlist2 != NULL && strcmp(*dirlist2, start) < 0)
            dirlist2++;
        if ((*dirlist1 == NULL) || (*dirlist2 == NULL))
            bb_error_msg(bb_msg_invalid_arg, "NULL", "-S");
    }

    /* Now that both dirlist1 and dirlist2 contain sorted directory
     * listings, we can start to go through dirlist1. If both listings
     * contain the same file, then do a normal diff. Otherwise, behaviour
     * is determined by whether the -N flag is set. */
    while (*dirlist1 != NULL || *dirlist2 != NULL) {
        dp1 = *dirlist1;
        dp2 = *dirlist2;
        pos = dp1 == NULL ? 1 : dp2 == NULL ? -1 : strcmp(dp1, dp2);
        if (pos == 0) {
            do_diff(p1, dp1, p2, dp2);
            dirlist1++;
            dirlist2++;
        } else if (pos < 0) {
            if (cmd_flags & FLAG_N)
                do_diff(p1, dp1, p2, NULL);
            else
                print_only(p1, strlen(p1) + 1, dp1);
            dirlist1++;
        } else {
            if (cmd_flags & FLAG_N)
                do_diff(p1, NULL, p2, dp2);
            else
                print_only(p2, strlen(p2) + 1, dp2);
            dirlist2++;
        }
    }
}
#endif



int diff_main(int argc, char **argv)
{
    int gotstdin = 0;

    char *U_opt;
    llist_t *L_arg = NULL;

    bb_opt_complementally = "L::";
    cmd_flags =
        bb_getopt_ulflags(argc, argv, "abdiL:NqrsS:tTU:wu", &L_arg, &start,
                          &U_opt);

    if (cmd_flags & FLAG_L) {
        while (L_arg) {
            if (label[0] == NULL)
                label[0] = L_arg->data;
            else if (label[1] == NULL)
                label[1] = L_arg->data;
            else
                bb_show_usage();

            L_arg = L_arg->link;
        }

        /* If both label[0] and label[1] were set, they need to be swapped. */
        if (label[0] && label[1]) {
            char *tmp;

            tmp = label[1];
            label[1] = label[0];
            label[0] = tmp;
        }
    }

    context = 3;        /* This is the default number of lines of context. */
    if (cmd_flags & FLAG_U) {
        context = bb_xgetlarg(U_opt, 10, 1, INT_MAX);
    }
    argc -= optind;
    argv += optind;

    /*
     * Do sanity checks, fill in stb1 and stb2 and call the appropriate
     * driver routine.  Both drivers use the contents of stb1 and stb2.
     */
    if (argc < 2) {
        bb_error_msg("Missing filename");
        bb_show_usage();
    }
    if (strcmp(argv[0], "-") == 0) {
        fstat(STDIN_FILENO, &stb1);
        gotstdin = 1;
    } else
        xstat(argv[0], &stb1);
    if (strcmp(argv[1], "-") == 0) {
        fstat(STDIN_FILENO, &stb2);
        gotstdin = 1;
    } else
        xstat(argv[1], &stb2);
    if (gotstdin && (S_ISDIR(stb1.st_mode) || S_ISDIR(stb2.st_mode)))
        bb_error_msg_and_die("Can't compare - to a directory");
    if (S_ISDIR(stb1.st_mode) && S_ISDIR(stb2.st_mode)) {
#if ENABLE_FEATURE_DIFF_DIR
        diffdir(argv[0], argv[1]);
#else
        bb_error_msg_and_die("Directory comparison not supported");
#endif
    } else {
        if (S_ISDIR(stb1.st_mode)) {
            argv[0] = concat_path_file(argv[0], argv[1]);
            xstat(argv[0], &stb1);
        }
        if (S_ISDIR(stb2.st_mode)) {
            argv[1] = concat_path_file(argv[1], argv[0]);
            xstat(argv[1], &stb2);
        }
        print_status(diffreg(argv[0], argv[1], 0), argv[0], argv[1], NULL);
    }
    exit(status);
}