/* 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 "libbb.h"

// #define FSIZE_MAX 32768

/* NOINLINEs added to prevent gcc from merging too much into diffreg()
 * (it bites more than it can (efficiently) chew). */

/*
 * Output flags
 */
enum {
        /* Print a header/footer between files */
        /* D_HEADER = 1, - unused */
        /* Treat file as empty (/dev/null) */
        D_EMPTY1 = 2 * ENABLE_FEATURE_DIFF_DIR,
        D_EMPTY2 = 4 * ENABLE_FEATURE_DIFF_DIR,
};

/*
 * 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_ISDIR1 - path1 a dir, path2 a file
 * D_ISDIR2 - 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) - unused */
#define D_ISDIR1        (1 << 4)
#define D_ISDIR2        (1 << 5)
#define D_ERROR         (1 << 6)
#define D_SKIPPED1      (1 << 7)
#define D_SKIPPED2      (1 << 8)

/* Command line options */
#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)


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

struct line {
        int serial;
        int value;
};

/*
 * 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 */
};


#define g_read_buf bb_common_bufsiz1

struct globals {
        bool anychange;
        smallint exit_status;
        int opt_U_context;
        size_t max_context;     /* size of context_vec_start */
        IF_FEATURE_DIFF_DIR(int dl_count;)
        IF_FEATURE_DIFF_DIR(char **dl;)
        char *opt_S_start;
        const char *label1;
        const char *label2;
        int *J;                 /* will be overlaid on class */
        int clen;
        int pref, suff;         /* length of prefix and suffix */
        int nlen[2];
        int slen[2];
        int clistlen;           /* the length of clist */
        struct cand *clist;     /* merely a free storage pot for candidates */
        long *ixnew;            /* will be overlaid on nfile[1] */
        long *ixold;            /* will be overlaid on klist */
        struct line *nfile[2];
        struct line *sfile[2];  /* shortened by pruning common prefix/suffix */
        struct context_vec *context_vec_start;
        struct context_vec *context_vec_end;
        struct context_vec *context_vec_ptr;
        char *tempname1, *tempname2;
        struct stat stb1, stb2;
};
#define G (*ptr_to_globals)
#define anychange          (G.anychange         )
#define exit_status        (G.exit_status       )
#define opt_U_context      (G.opt_U_context     )
#define max_context        (G.max_context       )
#define dl_count           (G.dl_count          )
#define dl                 (G.dl                )
#define opt_S_start        (G.opt_S_start       )
#define label1             (G.label1            )
#define label2             (G.label2            )
#define J                  (G.J                 )
#define clen               (G.clen              )
#define pref               (G.pref              )
#define suff               (G.suff              )
#define nlen               (G.nlen              )
#define slen               (G.slen              )
#define clistlen           (G.clistlen          )
#define clist              (G.clist             )
#define ixnew              (G.ixnew             )
#define ixold              (G.ixold             )
#define nfile              (G.nfile             )
#define sfile              (G.sfile             )
#define context_vec_start  (G.context_vec_start )
#define context_vec_end    (G.context_vec_end   )
#define context_vec_ptr    (G.context_vec_ptr   )
#define stb1               (G.stb1              )
#define stb2               (G.stb2              )
#define tempname1          (G.tempname1         )
#define tempname2          (G.tempname2         )
#define INIT_G() do { \
        SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
        opt_U_context = 3; \
        max_context = 64; \
} while (0)


#if ENABLE_FEATURE_DIFF_DIR
static void print_only(const char *path, const char *entry)
{
        printf("Only in %s: %s\n", path, entry);
}
#endif


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

        switch (val) {
/*      case D_ONLY:
                print_only(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 (option_mask32 & FLAG_q)
                        printf("Files %s and %s differ\n", _path1, _path2);
                break;
        case D_SAME:
                if (option_mask32 & FLAG_s)
                        printf("Files %s and %s are identical\n", _path1, _path2);
                break;
        case D_ISDIR1:
                printf("File %s is a %s while file %s is a %s\n",
                           _path1, "directory", _path2, "regular file");
                break;
        case D_ISDIR2:
                printf("File %s is a %s while file %s is a %s\n",
                           _path1, "regular file", _path2, "directory");
                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);
        }
*/
}


/* Read line, return its nonzero hash. Return 0 if EOF.
 *
 * Hash function taken from Robert Sedgewick, Algorithms in C, 3d ed., p 578.
 */
static ALWAYS_INLINE int fiddle_sum(int sum, int t)
{
        return sum * 127 + t;
}
static int readhash(FILE *fp)
{
        int i, t, space;
        int sum;

        sum = 1;
        space = 0;
        i = 0;
        if (!(option_mask32 & (FLAG_b | FLAG_w))) {
                while ((t = getc(fp)) != '\n') {
                        if (t == EOF) {
                                if (i == 0)
                                        return 0;
                                break;
                        }
                        sum = fiddle_sum(sum, t);
                        i = 1;
                }
        } else {
                while (1) {
                        switch (t = getc(fp)) {
                        case '\t':
                        case '\r':
                        case '\v':
                        case '\f':
                        case ' ':
                                space = 1;
                                continue;
                        default:
                                if (space && !(option_mask32 & FLAG_w)) {
                                        i = 1;
                                        space = 0;
                                }
                                sum = fiddle_sum(sum, t);
                                i = 1;
                                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);
}


/* Our diff implementation is using seek.
 * When we meet non-seekable file, we must make a temp copy.
 */
static char *make_temp(FILE *f, struct stat *sb)
{
        char *name;
        int fd;

        if (S_ISREG(sb->st_mode) || S_ISBLK(sb->st_mode))
                return NULL;
        name = xstrdup("/tmp/difXXXXXX");
        fd = mkstemp(name);
        if (fd < 0)
                bb_perror_msg_and_die("mkstemp");
        if (bb_copyfd_eof(fileno(f), fd) < 0) {
 clean_up:
                unlink(name);
                xfunc_die(); /* error message is printed by bb_copyfd_eof */
        }
        fstat(fd, sb);
        close(fd);
        if (freopen(name, "r+", f) == NULL) {
                bb_perror_msg("freopen");
                goto clean_up;
        }
        return name;
}


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

        /* Prevent making copies for "/dev/null" (too common) */
        /* Deal with input from pipes etc */
        tempname1 = make_temp(f1, &stb1);
        tempname2 = make_temp(f2, &stb2);
        if (stb1.st_size != stb2.st_size) {
                return 1;
        }
        while (1) {
                i = fread(g_read_buf,                    1, COMMON_BUFSIZE/2, f1);
                j = fread(g_read_buf + COMMON_BUFSIZE/2, 1, COMMON_BUFSIZE/2, f2);
                if (i != j)
                        return 1;
                if (i == 0)
                        return (ferror(f1) || ferror(f2)) ? -1 : 0;
                if (memcmp(g_read_buf,
                           g_read_buf + COMMON_BUFSIZE/2, i) != 0)
                        return 1;
        }
}


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

        rewind(fp);

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

        p = xmalloc((sz + 3) * sizeof(p[0]));
        j = 0;
        while ((h = readhash(fp)) != 0) { /* while not EOF */
                if (j == sz) {
                        sz = sz * 3 / 2;
                        p = xrealloc(p, (sz + 3) * sizeof(p[0]));
                }
                p[++j].value = h;
        }
        nlen[i] = j;
        nfile[i] = p;
}


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

        for (pref = 0; pref < nlen[0] && pref < nlen[1] &&
                nfile[0][pref + 1].value == nfile[1][pref + 1].value; pref++)
                continue;
        for (suff = 0; suff < nlen[0] - pref && suff < nlen[1] - pref &&
                nfile[0][nlen[0] - suff].value == nfile[1][nlen[1] - suff].value;
                suff++)
                continue;
        for (j = 0; j < 2; j++) {
                sfile[j] = nfile[j] + pref;
                slen[j] = nlen[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;

        if (n == 0)
                return 0;
        x = 1;
        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 =
                (option_mask32 & 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 <= nlen[0]; i++)
                J[i] = i <= pref ? i : i > nlen[0] - suff ? i + nlen[1] - nlen[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 NOINLINE 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 <= nlen[0]; i++) {
                if (J[i] == 0) {
                        ixold[i] = ctold += skipline(f1);
                        continue;
                }
                while (j < J[i]) {
                        ixnew[j] = ctnew += skipline(f2);
                        j++;
                }
                if (option_mask32 & (FLAG_b | FLAG_w | FLAG_i)) {
                        while (1) {
                                c = getc(f1);
                                d = getc(f2);
                                /*
                                 * GNU diff ignores a missing newline
                                 * in one file if bflag || wflag.
                                 */
                                if ((option_mask32 & (FLAG_b | FLAG_w))
                                 && ((c == EOF && d == '\n') || (c == '\n' && d == EOF))
                                ) {
                                        break;
                                }
                                ctold++;
                                ctnew++;
                                if ((option_mask32 & FLAG_b) && isspace(c) && isspace(d)) {
                                        do {
                                                if (c == '\n')
                                                        break;
                                                ctold++;
                                                c = getc(f1);
                                        } while (isspace(c));
                                        do {
                                                if (d == '\n')
                                                        break;
                                                ctnew++;
                                                d = getc(f2);
                                        } while (isspace(d));
                                } else if (option_mask32 & 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++;
                                c = getc(f1);
                                d = getc(f2);
                                if (c != d) {
                                        J[i] = 0;
                                        if (c != '\n' && c != EOF)
                                                ctold += skipline(f1);
/* was buggy? "if (d != '\n' && c != EOF)" */
                                        if (d != '\n' && d != EOF)
                                                ctnew += skipline(f2);
                                        break;
                                }
                                if (c == '\n' || c == EOF)
                                        break;
                        }
                }
                ixold[i] = ctold;
                ixnew[j] = ctnew;
                j++;
        }
        for (; j <= nlen[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 void fetch(long *f, int a, int b, FILE *lb, int ch)
{
        int i, j, c, lastc, col, nc;

        if (a > b)
                return;
        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 (option_mask32 & FLAG_T)
                                putchar('\t');
                }
                col = 0;
                for (j = 0, lastc = '\0'; j < nc; j++, lastc = c) {
                        c = getc(lb);
                        if (c == EOF) {
                                printf("\n\\ No newline at end of file\n");
                                return;
                        }
                        if (c == '\t' && (option_mask32 & FLAG_t)) {
                                do {
                                        putchar(' ');
                                } while (++col & 7);
                        } else {
                                putchar(c);
                                col++;
                        }
                }
        }
}


#if ENABLE_FEATURE_DIFF_BINARY
static int asciifile(FILE *f)
{
        int i, cnt;

        if (option_mask32 & FLAG_a)
                return 1;
        rewind(f);
        cnt = fread(g_read_buf, 1, COMMON_BUFSIZE, f);
        for (i = 0; i < cnt; i++) {
                if (!isprint(g_read_buf[i])
                 && !isspace(g_read_buf[i])
                ) {
                        return 0;
                }
        }
        return 1;
}
#else
#define asciifile(f) 1
#endif


/* 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 - opt_U_context);
        upb = MIN(nlen[0], context_vec_ptr->b + opt_U_context);
        lowc = MAX(1, cvp->c - opt_U_context);
        upd = MIN(nlen[1], context_vec_ptr->d + opt_U_context);

        printf("@@ -");
        uni_range(lowa, upb);
        printf(" +");
        uni_range(lowc, upd);
        printf(" @@\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() seeks!
                        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 (label1)
                printf("--- %s\n", label1);
        else
                printf("--- %s\t%s", file1, ctime(&stb1.st_mtime));
        if (label2)
                printf("+++ %s\n", label2);
        else
                printf("+++ %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 than 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(const char *file1, FILE *f1, const char *file2, FILE *f2,
                        int a, int b, int c, int d)
{
        if ((a > b && c > d) || (option_mask32 & FLAG_q)) {
                anychange = 1;
                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);
        } else if (a > context_vec_ptr->b + (2 * opt_U_context) + 1
                && c > context_vec_ptr->d + (2 * opt_U_context) + 1
        ) {
                /*
                 * If this change is more than 'context' lines from the
                 * previous change, dump the record and reset it.
                 */
// dump_unified_vec() seeks!
                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;
        anychange = 1;
}


static void output(const char *file1, FILE *f1, const 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 = nlen[0];
        J[0] = 0;
        J[m + 1] = nlen[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() seeks!
                change(file1, f1, file2, f2, i0, i1, j00, j01);
        }
        if (m == 0) {
// change() seeks!
                change(file1, f1, file2, f2, 1, 0, 1, nlen[1]);
        }
        if (anychange != 0 && !(option_mask32 & FLAG_q)) {
// dump_unified_vec() seeks!
                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 in 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.
 */
/* NB: files can be not REGular. The only sure thing that they

 * are not both DIRectories. */
static unsigned diffreg(const char *file1, const char *file2, int flags)
{
        int *member;     /* will be overlaid on nfile[1] */
        int *class;      /* will be overlaid on nfile[0] */
        int *klist;      /* will be overlaid on nfile[0] after class */
        FILE *f1;
        FILE *f2;
        unsigned rval;
        int i;

        anychange = 0;
        context_vec_ptr = context_vec_start - 1;
        tempname1 = tempname2 = NULL;

        /* Is any of them a directory? Then it's simple */
        if (S_ISDIR(stb1.st_mode) != S_ISDIR(stb2.st_mode))
                return (S_ISDIR(stb1.st_mode) ? D_ISDIR1 : D_ISDIR2);

        /* None of them are directories */
        rval = D_SAME;

        if (flags & D_EMPTY1)
                /* can't be stdin, but xfopen_stdin() is smaller code */
                file1 = bb_dev_null;
        f1 = xfopen_stdin(file1);
        if (flags & D_EMPTY2)
                file2 = bb_dev_null;
        f2 = xfopen_stdin(file2);

        /* NB: if D_EMPTY1/2 is set, other file is always a regular file,
         * not pipe/fifo/chardev/etc - D_EMPTY is used by "diff -r" only,
         * and it never diffs non-ordinary files in subdirs. */
        if (!(flags & (D_EMPTY1 | D_EMPTY2))) {
                /* Quick check whether they are different */
                /* NB: copies non-REG files to tempfiles and fills tempname1/2 */
                i = files_differ(f1, f2);
                if (i != 1) { /* not different? */
                        if (i != 0) /* error? */
                                exit_status |= 2;
                        goto closem;
                }
        }

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

// Rewind inside!
        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 *) nfile[1];
        equiv(sfile[0], slen[0], sfile[1], slen[1], member);
//TODO: xrealloc_vector?
        member = xrealloc(member, (slen[1] + 2) * sizeof(int));

        class = (int *) nfile[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, (nlen[0] + 2) * sizeof(int));
        unravel(klist[i]);
        free(clist);
        free(klist);

        ixold = xrealloc(ixold, (nlen[0] + 2) * sizeof(long));
        ixnew = xrealloc(ixnew, (nlen[1] + 2) * sizeof(long));
// Rewind inside!
        check(f1, f2);
// Rewind inside!
        output(file1, f1, file2, f2);

 closem:
        if (anychange) {
                exit_status |= 1;
                if (rval == D_SAME)
                        rval = D_DIFFER;
        }
        fclose_if_not_stdin(f1);
        fclose_if_not_stdin(f2);
        if (tempname1) {
                unlink(tempname1);
                free(tempname1);
        }
        if (tempname2) {
                unlink(tempname2);
                free(tempname2);
        }
        return rval;
}


#if ENABLE_FEATURE_DIFF_DIR
static void do_diff(char *dir1, char *path1, char *dir2, char *path2)
{
        int flags = 0; /*D_HEADER;*/
        int val;
        char *fullpath1 = NULL; /* if -N */
        char *fullpath2 = NULL;

        if (path1)
                fullpath1 = concat_path_file(dir1, path1);
        if (path2)
                fullpath2 = concat_path_file(dir2, path2);

        if (!fullpath1 || stat(fullpath1, &stb1) != 0) {
                flags |= D_EMPTY1;
                memset(&stb1, 0, sizeof(stb1));
                if (path2) {
                        free(fullpath1);
                        fullpath1 = concat_path_file(dir1, path2);
                }
        }
        if (!fullpath2 || stat(fullpath2, &stb2) != 0) {
                flags |= D_EMPTY2;
                memset(&stb2, 0, sizeof(stb2));
                stb2.st_mode = stb1.st_mode;
                if (path1) {
                        free(fullpath2);
                        fullpath2 = concat_path_file(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);
                goto ret;
        }

        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 {
                /* Both files are either REGular or DIRectories */
                val = diffreg(fullpath1, fullpath2, flags);
        }

        print_status(val, fullpath1, fullpath2 /*, NULL*/);
 ret:
        free(fullpath1);
        free(fullpath2);
}
#endif


#if ENABLE_FEATURE_DIFF_DIR
/* This function adds a filename to dl, the directory listing. */
static int FAST_FUNC add_to_dirlist(const char *filename,
                struct stat *sb UNUSED_PARAM,
                void *userdata,
                int depth UNUSED_PARAM)
{
        dl = xrealloc_vector(dl, 5, dl_count);
        dl[dl_count] = xstrdup(filename + (int)(ptrdiff_t)userdata);
        dl_count++;
        return TRUE;
}


/* This returns a sorted directory listing. */
static char **get_recursive_dirlist(char *path)
{
        dl_count = 0;
        dl = xzalloc(sizeof(dl[0]));

        /* We need to trim root directory prefix.
         * Using void *userdata to specify its length,
         * add_to_dirlist will remove it. */
        if (option_mask32 & FLAG_r) {
                recursive_action(path, ACTION_RECURSE|ACTION_FOLLOWLINKS,
                                        add_to_dirlist, /* file_action */
                                        NULL, /* dir_action */
                                        (void*)(ptrdiff_t)(strlen(path) + 1),
                                        0);
        } else {
                DIR *dp;
                struct dirent *ep;

                dp = warn_opendir(path);
                while ((ep = readdir(dp))) {
                        if (!strcmp(ep->d_name, "..") || LONE_CHAR(ep->d_name, '.'))
                                continue;
                        add_to_dirlist(ep->d_name, NULL, (void*)(int)0, 0);
                }
                closedir(dp);
        }

        /* Sort dl alphabetically. */
        qsort_string_vector(dl, dl_count);

        dl[dl_count] = NULL;
        return dl;
}


static void diffdir(char *p1, char *p2)
{
        char **dirlist1, **dirlist2;
        char *dp1, *dp2;
        int pos;

        /* Check for trailing slashes. */
        dp1 = last_char_is(p1, '/');
        if (dp1 != NULL)
                *dp1 = '\0';
        dp2 = last_char_is(p2, '/');
        if (dp2 != NULL)
                *dp2 = '\0';

        /* Get directory listings for p1 and p2. */
        dirlist1 = get_recursive_dirlist(p1);
        dirlist2 = get_recursive_dirlist(p2);

        /* If -S was set, find the starting point. */
        if (opt_S_start) {
                while (*dirlist1 != NULL && strcmp(*dirlist1, opt_S_start) < 0)
                        dirlist1++;
                while (*dirlist2 != NULL && strcmp(*dirlist2, opt_S_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 (option_mask32 & FLAG_N)
                                do_diff(p1, dp1, p2, NULL);
                        else
                                print_only(p1, dp1);
                        dirlist1++;
                } else {
                        if (option_mask32 & FLAG_N)
                                do_diff(p1, NULL, p2, dp2);
                        else
                                print_only(p2, dp2);
                        dirlist2++;
                }
        }
}
#endif


int diff_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int diff_main(int argc UNUSED_PARAM, char **argv)
{
        int gotstdin = 0;
        char *f1, *f2;
        llist_t *L_arg = NULL;

        INIT_G();

        /* exactly 2 params; collect multiple -L <label>; -U N */
        opt_complementary = "=2:L::U+";
        getopt32(argv, "abdiL:NqrsS:tTU:wu"
                        "p" /* ignored (for compatibility) */,
                        &L_arg, &opt_S_start, &opt_U_context);
        /*argc -= optind;*/
        argv += optind;
        while (L_arg) {
                if (label1 && label2)
                        bb_show_usage();
                if (label1) /* then label2 is NULL */
                        label2 = label1;
                label1 = llist_pop(&L_arg);
        }

        /*
         * Do sanity checks, fill in stb1 and stb2 and call the appropriate
         * driver routine.  Both drivers use the contents of stb1 and stb2.
         */
        f1 = argv[0];
        f2 = argv[1];
        /* Compat: "diff file name_which_doesnt_exist" exits with 2 */
        xfunc_error_retval = 2;
        if (LONE_DASH(f1)) {
                fstat(STDIN_FILENO, &stb1);
                gotstdin++;
        } else
                xstat(f1, &stb1);
        if (LONE_DASH(f2)) {
                fstat(STDIN_FILENO, &stb2);
                gotstdin++;
        } else
                xstat(f2, &stb2);
        xfunc_error_retval = 1;

        if (gotstdin && (S_ISDIR(stb1.st_mode) || S_ISDIR(stb2.st_mode)))
                bb_error_msg_and_die("can't compare stdin to a directory");

        if (S_ISDIR(stb1.st_mode) && S_ISDIR(stb2.st_mode)) {
#if ENABLE_FEATURE_DIFF_DIR
                diffdir(f1, f2);
                return exit_status;
#else
                bb_error_msg_and_die("no support for directory comparison");
#endif
        }

        if (S_ISDIR(stb1.st_mode)) { /* "diff dir file" */
                /* NB: "diff dir      dir2/dir3/file" must become
                 *     "diff dir/file dir2/dir3/file" */
                char *slash = strrchr(f2, '/');
                f1 = concat_path_file(f1, slash ? slash + 1 : f2);
                xstat(f1, &stb1);
        }
        if (S_ISDIR(stb2.st_mode)) {
                char *slash = strrchr(f1, '/');
                f2 = concat_path_file(f2, slash ? slash + 1 : f1);
                xstat(f2, &stb2);
        }

        /* diffreg can get non-regular files here,
         * they are not both DIRestories */
        print_status((gotstdin > 1 ? D_SAME : diffreg(f1, f2, 0)),
                        f1, f2 /*, NULL*/);
        return exit_status;
}