source: MondoRescue/branches/3.2/mindi-busybox/editors/diff.c@ 3186

/* vi: set sw=4 ts=4: */
/*
 * Mini diff implementation for busybox, adapted from OpenBSD diff.
 *
 * Copyright (C) 2010 by Matheus Izvekov <mizvekov@gmail.com>
 * 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 source tree.
 */

/*
 * 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.
 */

#include "libbb.h"

#if 0
//#define dbg_error_msg(...) bb_error_msg(__VA_ARGS__)
#else
#define dbg_error_msg(...) ((void)0)
#endif

enum {                  /* print_status() and diffreg() return values */
    STATUS_SAME,    /* files are the same */
    STATUS_DIFFER,  /* files differ */
    STATUS_BINARY,  /* binary files differ */
};

enum {                  /* Commandline flags */
    FLAG_a,
    FLAG_b,
    FLAG_d,
    FLAG_i,
    FLAG_L,         /* never used, handled by getopt32 */
    FLAG_N,
    FLAG_q,
    FLAG_r,
    FLAG_s,
    FLAG_S,         /* never used, handled by getopt32 */
    FLAG_t,
    FLAG_T,
    FLAG_U,         /* never used, handled by getopt32 */
    FLAG_w,
    FLAG_u,         /* ignored, this is the default */
    FLAG_p,         /* not implemented */
    FLAG_B,
    FLAG_E,         /* not implemented */
};
#define FLAG(x) (1 << FLAG_##x)

/* We cache file position to avoid excessive seeking */
typedef struct FILE_and_pos_t {
    FILE *ft_fp;
    off_t ft_pos;
} FILE_and_pos_t;

struct globals {
    smallint exit_status;
    int opt_U_context;
    const char *other_dir;
    char *label[2];
    struct stat stb[2];
};
#define G (*ptr_to_globals)
#define exit_status        (G.exit_status       )
#define opt_U_context      (G.opt_U_context     )
#define label              (G.label             )
#define stb                (G.stb               )
#define INIT_G() do { \
    SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
    opt_U_context = 3; \
} while (0)

typedef int token_t;

enum {
    /* Public */
    TOK_EMPTY = 1 << 9,  /* Line fully processed, you can proceed to the next */
    TOK_EOF   = 1 << 10, /* File ended */
    /* Private (Only to be used by read_token() */
    TOK_EOL   = 1 << 11, /* we saw EOL (sticky) */
    TOK_SPACE = 1 << 12, /* used -b code, means we are skipping spaces */
    SHIFT_EOF = (sizeof(token_t)*8 - 8) - 1,
    CHAR_MASK = 0x1ff,   /* 8th bit is used to distinguish EOF from 0xff */
};

/* Restores full EOF from one 8th bit: */
//#define TOK2CHAR(t) (((t) << SHIFT_EOF) >> SHIFT_EOF)
/* We don't really need the above, we only need to have EOF != any_real_char: */
#define TOK2CHAR(t) ((t) & CHAR_MASK)

static void seek_ft(FILE_and_pos_t *ft, off_t pos)
{
    if (ft->ft_pos != pos) {
        ft->ft_pos = pos;
        fseeko(ft->ft_fp, pos, SEEK_SET);
    }
}

/* Reads tokens from given fp, handling -b and -w flags
 * The user must reset tok every line start
 */
static int read_token(FILE_and_pos_t *ft, token_t tok)
{
    tok |= TOK_EMPTY;
    while (!(tok & TOK_EOL)) {
        bool is_space;
        int t;

        t = fgetc(ft->ft_fp);
        if (t != EOF)
            ft->ft_pos++;
        is_space = (t == EOF || isspace(t));

        /* If t == EOF (-1), set both TOK_EOF and TOK_EOL */
        tok |= (t & (TOK_EOF + TOK_EOL));
        /* Only EOL? */
        if (t == '\n')
            tok |= TOK_EOL;

        if (option_mask32 & FLAG(i)) /* Handcoded tolower() */
            t = (t >= 'A' && t <= 'Z') ? t - ('A' - 'a') : t;

        if ((option_mask32 & FLAG(w)) && is_space)
            continue;

        /* Trim char value to low 9 bits */
        t &= CHAR_MASK;

        if (option_mask32 & FLAG(b)) {
            /* Was prev char whitespace? */
            if (tok & TOK_SPACE) { /* yes */
                if (is_space) /* this one too, ignore it */
                    continue;
                tok &= ~TOK_SPACE;
            } else if (is_space) {
                /* 1st whitespace char.
                 * Set TOK_SPACE and replace char by ' ' */
                t = TOK_SPACE + ' ';
            }
        }
        /* Clear EMPTY */
        tok &= ~(TOK_EMPTY + CHAR_MASK);
        /* Assign char value (low 9 bits) and maybe set TOK_SPACE */
        tok |= t;
        break;
    }
#if 0
    bb_error_msg("fp:%p tok:%x '%c'%s%s%s%s", fp, tok, tok & 0xff
        , tok & TOK_EOF ? " EOF" : ""
        , tok & TOK_EOL ? " EOL" : ""
        , tok & TOK_EMPTY ? " EMPTY" : ""
        , tok & TOK_SPACE ? " SPACE" : ""
    );
#endif
    return tok;
}

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

static int search(const int *c, int k, int y, const struct cand *list)
{
    int i, j;

    if (list[c[k]].y < y)  /* quick look for typical case */
        return k + 1;

    for (i = 0, j = k + 1;;) {
        const int l = (i + j) >> 1;
        if (l > i) {
            const int t = list[c[l]].y;
            if (t > y)
                j = l;
            else if (t < y)
                i = l;
            else
                return l;
        } else
            return l + 1;
    }
}

static unsigned isqrt(unsigned n)
{
    unsigned x = 1;
    while (1) {
        const unsigned y = x;
        x = ((n / x) + x) >> 1;
        if (x <= (y + 1) && x >= (y - 1))
            return x;
    }
}

static void stone(const int *a, int n, const int *b, int *J, int pref)
{
    const unsigned isq = isqrt(n);
    const unsigned bound =
        (option_mask32 & FLAG(d)) ? UINT_MAX : MAX(256, isq);
    int clen = 1;
    int clistlen = 100;
    int k = 0;
    struct cand *clist = xzalloc(clistlen * sizeof(clist[0]));
    struct cand cand;
    struct cand *q;
    int *klist = xzalloc((n + 2) * sizeof(klist[0]));
    /*clist[0] = (struct cand){0}; - xzalloc did it */
    /*klist[0] = 0; */

    for (cand.x = 1; cand.x <= n; cand.x++) {
        int j = a[cand.x], oldl = 0;
        unsigned numtries = 0;
        if (j == 0)
            continue;
        cand.y = -b[j];
        cand.pred = klist[0];
        do {
            int l, tc;
            if (cand.y <= clist[cand.pred].y)
                continue;
            l = search(klist, k, cand.y, clist);
            if (l != oldl + 1)
                cand.pred = klist[l - 1];
            if (l <= k && clist[klist[l]].y <= cand.y)
                continue;
            if (clen == clistlen) {
                clistlen = clistlen * 11 / 10;
                clist = xrealloc(clist, clistlen * sizeof(clist[0]));
            }
            clist[clen] = cand;
            tc = klist[l];
            klist[l] = clen++;
            if (l <= k) {
                cand.pred = tc;
                oldl = l;
                numtries++;
            } else {
                k++;
                break;
            }
        } while ((cand.y = b[++j]) > 0 && numtries < bound);
    }
    /* Unravel */
    for (q = clist + klist[k]; q->y; q = clist + q->pred)
        J[q->x + pref] = q->y + pref;
    free(klist);
    free(clist);
}

struct line {
    /* 'serial' is not used in the begining, so we reuse it
     * to store line offsets, thus reducing memory pressure
     */
    union {
        unsigned serial;
        off_t offset;
    };
    unsigned value;
};

static void equiv(struct line *a, int n, struct line *b, int m, int *c)
{
    int i = 1, 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 void unsort(const struct line *f, int l, int *b)
{
    int i;
    int *a = xmalloc((l + 1) * sizeof(a[0]));
    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 line_compar(const void *a, const void *b)
{
#define l0 ((const struct line*)a)
#define l1 ((const struct line*)b)
    int r = l0->value - l1->value;
    if (r)
        return r;
    return l0->serial - l1->serial;
#undef l0
#undef l1
}

static void fetch(FILE_and_pos_t *ft, const off_t *ix, int a, int b, int ch)
{
    int i, j, col;
    for (i = a; i <= b; i++) {
        seek_ft(ft, ix[i - 1]);
        putchar(ch);
        if (option_mask32 & FLAG(T))
            putchar('\t');
        for (j = 0, col = 0; j < ix[i] - ix[i - 1]; j++) {
            int c = fgetc(ft->ft_fp);
            if (c == EOF) {
                printf("\n\\ No newline at end of file\n");
                return;
            }
            ft->ft_pos++;
            if (c == '\t' && (option_mask32 & FLAG(t)))
                do putchar(' '); while (++col & 7);
            else {
                putchar(c);
                col++;
            }
        }
    }
}

/* Creates the match vector J, where J[i] is the index
 * of the line in the new file corresponding to the line i
 * in the old file. Lines start at 1 instead of 0, that value
 * being used instead to denote no corresponding line.
 * This vector is dynamically allocated and must be freed by the caller.
 *
 * * fp is an input parameter, where fp[0] and fp[1] are the open
 *   old file and new file respectively.
 * * nlen is an output variable, where nlen[0] and nlen[1]
 *   gets the number of lines in the old and new file respectively.
 * * ix is an output variable, where ix[0] and ix[1] gets
 *   assigned dynamically allocated vectors of the offsets of the lines
 *   of the old and new file respectively. These must be freed by the caller.
 */
static NOINLINE int *create_J(FILE_and_pos_t ft[2], int nlen[2], off_t *ix[2])
{
    int *J, slen[2], *class, *member;
    struct line *nfile[2], *sfile[2];
    int pref = 0, suff = 0, i, j, delta;

    /* Lines of both files are hashed, and in the process
     * their offsets are stored in the array ix[fileno]
     * where fileno == 0 points to the old file, and
     * fileno == 1 points to the new one.
     */
    for (i = 0; i < 2; i++) {
        unsigned hash;
        token_t tok;
        size_t sz = 100;
        nfile[i] = xmalloc((sz + 3) * sizeof(nfile[i][0]));
        /* ft gets here without the correct position, cant use seek_ft */
        ft[i].ft_pos = 0;
        fseeko(ft[i].ft_fp, 0, SEEK_SET);

        nlen[i] = 0;
        /* We could zalloc nfile, but then zalloc starts showing in gprof at ~1% */
        nfile[i][0].offset = 0;
        goto start; /* saves code */
        while (1) {
            tok = read_token(&ft[i], tok);
            if (!(tok & TOK_EMPTY)) {
                /* Hash algorithm taken from Robert Sedgewick, Algorithms in C, 3d ed., p 578. */
                /*hash = hash * 128 - hash + TOK2CHAR(tok);
                 * gcc insists on optimizing above to "hash * 127 + ...", thus... */
                unsigned o = hash - TOK2CHAR(tok);
                hash = hash * 128 - o; /* we want SPEED here */
                continue;
            }
            if (nlen[i]++ == sz) {
                sz = sz * 3 / 2;
                nfile[i] = xrealloc(nfile[i], (sz + 3) * sizeof(nfile[i][0]));
            }
            /* line_compar needs hashes fit into positive int */
            nfile[i][nlen[i]].value = hash & INT_MAX;
            /* like ftello(ft[i].ft_fp) but faster (avoids lseek syscall) */
            nfile[i][nlen[i]].offset = ft[i].ft_pos;
            if (tok & TOK_EOF) {
                /* EOF counts as a token, so we have to adjust it here */
                nfile[i][nlen[i]].offset++;
                break;
            }
start:
            hash = tok = 0;
        }
        /* Exclude lone EOF line from the end of the file, to make fetch()'s job easier */
        if (nfile[i][nlen[i]].offset - nfile[i][nlen[i] - 1].offset == 1)
            nlen[i]--;
        /* Now we copy the line offsets into ix */
        ix[i] = xmalloc((nlen[i] + 2) * sizeof(ix[i][0]));
        for (j = 0; j < nlen[i] + 1; j++)
            ix[i][j] = nfile[i][j].offset;
    }

    /* length of prefix and suffix is calculated */
    for (; pref < nlen[0] && pref < nlen[1] &&
           nfile[0][pref + 1].value == nfile[1][pref + 1].value;
           pref++);
    for (; suff < nlen[0] - pref && suff < nlen[1] - pref &&
           nfile[0][nlen[0] - suff].value == nfile[1][nlen[1] - suff].value;
           suff++);
    /* Arrays are pruned by the suffix and prefix length,
     * the result being sorted and stored in sfile[fileno],
     * and their sizes are stored in slen[fileno]
     */
    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;
        qsort(sfile[j] + 1, slen[j], sizeof(*sfile[j]), line_compar);
    }
    /* nfile arrays are reused to reduce memory pressure
     * The #if zeroed out section performs the same task as the
     * one in the #else section.
     * Peak memory usage is higher, but one array copy is avoided
     * by not using unsort()
     */
#if 0
    member = xmalloc((slen[1] + 2) * sizeof(member[0]));
    equiv(sfile[0], slen[0], sfile[1], slen[1], member);
    free(nfile[1]);

    class = xmalloc((slen[0] + 1) * sizeof(class[0]));
    for (i = 1; i <= slen[0]; i++) /* Unsorting */
        class[sfile[0][i].serial] = sfile[0][i].value;
    free(nfile[0]);
#else
    member = (int *)nfile[1];
    equiv(sfile[0], slen[0], sfile[1], slen[1], member);
    member = xrealloc(member, (slen[1] + 2) * sizeof(member[0]));

    class = (int *)nfile[0];
    unsort(sfile[0], slen[0], (int *)nfile[0]);
    class = xrealloc(class, (slen[0] + 2) * sizeof(class[0]));
#endif
    J = xmalloc((nlen[0] + 2) * sizeof(J[0]));
    /* The elements of J which fall inside the prefix and suffix regions
     * are marked as unchanged, while the ones which fall outside
     * are initialized with 0 (no matches), so that function stone can
     * then assign them their right values
     */
    for (i = 0, delta = nlen[1] - nlen[0]; i <= nlen[0]; i++)
        J[i] = i <= pref            ?  i :
               i > (nlen[0] - suff) ? (i + delta) : 0;
    /* Here the magic is performed */
    stone(class, slen[0], member, J, pref);
    J[nlen[0] + 1] = nlen[1] + 1;

    free(class);
    free(member);

    /* Both files are rescanned, in an effort to find any lines
     * which, due to limitations intrinsic to any hashing algorithm,
     * are different but ended up confounded as the same
     */
    for (i = 1; i <= nlen[0]; i++) {
        if (!J[i])
            continue;

        seek_ft(&ft[0], ix[0][i - 1]);
        seek_ft(&ft[1], ix[1][J[i] - 1]);

        for (j = J[i]; i <= nlen[0] && J[i] == j; i++, j++) {
            token_t tok0 = 0, tok1 = 0;
            do {
                tok0 = read_token(&ft[0], tok0);
                tok1 = read_token(&ft[1], tok1);

                if (((tok0 ^ tok1) & TOK_EMPTY) != 0 /* one is empty (not both) */
                 || (!(tok0 & TOK_EMPTY) && TOK2CHAR(tok0) != TOK2CHAR(tok1))
                ) {
                    J[i] = 0; /* Break the correspondence */
                }
            } while (!(tok0 & tok1 & TOK_EMPTY));
        }
    }

    return J;
}

static bool diff(FILE* fp[2], char *file[2])
{
    int nlen[2];
    off_t *ix[2];
    FILE_and_pos_t ft[2];
    typedef struct { int a, b; } vec_t[2];
    vec_t *vec = NULL;
    int i = 1, j, k, idx = -1;
    bool anychange = false;
    int *J;

    ft[0].ft_fp = fp[0];
    ft[1].ft_fp = fp[1];
    /* note that ft[i].ft_pos is unintitalized, create_J()
     * must not assume otherwise */
    J = create_J(ft, nlen, ix);

    do {
        bool nonempty = false;

        while (1) {
            vec_t v;

            for (v[0].a = i; v[0].a <= nlen[0] && J[v[0].a] == J[v[0].a - 1] + 1; v[0].a++)
                continue;
            v[1].a = J[v[0].a - 1] + 1;

            for (v[0].b = v[0].a - 1; v[0].b < nlen[0] && !J[v[0].b + 1]; v[0].b++)
                continue;
            v[1].b = J[v[0].b + 1] - 1;
            /*
             * 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.
             */
            if (v[0].a <= v[0].b || v[1].a <= v[1].b) {
                /*
                 * If this change is more than 'context' lines from the
                 * previous change, dump the record and reset it.
                 */
                int ct = (2 * opt_U_context) + 1;
                if (idx >= 0
                 && v[0].a > vec[idx][0].b + ct
                 && v[1].a > vec[idx][1].b + ct
                ) {
                    break;
                }

                for (j = 0; j < 2; j++)
                    for (k = v[j].a; k < v[j].b; k++)
                        nonempty |= (ix[j][k+1] - ix[j][k] != 1);

                vec = xrealloc_vector(vec, 6, ++idx);
                memcpy(vec[idx], v, sizeof(v));
            }

            i = v[0].b + 1;
            if (i > nlen[0])
                break;
            J[v[0].b] = v[1].b;
        }
        if (idx < 0 || ((option_mask32 & FLAG(B)) && !nonempty))
            goto cont;
        if (!(option_mask32 & FLAG(q))) {
            int lowa;
            vec_t span, *cvp = vec;

            if (!anychange) {
                /* Print the context/unidiff header first time through */
                printf("--- %s\n", label[0] ? label[0] : file[0]);
                printf("+++ %s\n", label[1] ? label[1] : file[1]);
            }

            printf("@@");
            for (j = 0; j < 2; j++) {
                int a = span[j].a = MAX(1, (*cvp)[j].a - opt_U_context);
                int b = span[j].b = MIN(nlen[j], vec[idx][j].b + opt_U_context);

                printf(" %c%d", j ? '+' : '-', MIN(a, b));
                if (a == b)
                    continue;
                printf(",%d", (a < b) ? b - a + 1 : 0);
            }
            printf(" @@\n");
            /*
             * Output changes in "unified" diff format--the old and new lines
             * are printed together.
             */
            for (lowa = span[0].a; ; lowa = (*cvp++)[0].b + 1) {
                bool end = cvp > &vec[idx];
                fetch(&ft[0], ix[0], lowa, end ? span[0].b : (*cvp)[0].a - 1, ' ');
                if (end)
                    break;
                for (j = 0; j < 2; j++)
                    fetch(&ft[j], ix[j], (*cvp)[j].a, (*cvp)[j].b, j ? '+' : '-');
            }
        }
        anychange = true;
 cont:
        idx = -1;
    } while (i <= nlen[0]);

    free(vec);
    free(ix[0]);
    free(ix[1]);
    free(J);
    return anychange;
}

static int diffreg(char *file[2])
{
    FILE *fp[2] = { stdin, stdin };
    bool binary = false, differ = false;
    int status = STATUS_SAME, i;

    for (i = 0; i < 2; i++) {
        int fd = open_or_warn_stdin(file[i]);
        if (fd == -1)
            goto out;
        /* Our diff implementation is using seek.
         * When we meet non-seekable file, we must make a temp copy.
         */
        if (lseek(fd, 0, SEEK_SET) == -1 && errno == ESPIPE) {
            char name[] = "/tmp/difXXXXXX";
            int fd_tmp = xmkstemp(name);

            unlink(name);
            if (bb_copyfd_eof(fd, fd_tmp) < 0)
                xfunc_die();
            if (fd) /* Prevents closing of stdin */
                close(fd);
            fd = fd_tmp;
        }
        fp[i] = fdopen(fd, "r");
    }

    while (1) {
        const size_t sz = COMMON_BUFSIZE / 2;
        char *const buf0 = bb_common_bufsiz1;
        char *const buf1 = buf0 + sz;
        int j, k;
        i = fread(buf0, 1, sz, fp[0]);
        j = fread(buf1, 1, sz, fp[1]);
        if (i != j) {
            differ = true;
            i = MIN(i, j);
        }
        if (i == 0)
            break;
        for (k = 0; k < i; k++) {
            if (!buf0[k] || !buf1[k])
                binary = true;
            if (buf0[k] != buf1[k])
                differ = true;
        }
    }
    if (differ) {
        if (binary && !(option_mask32 & FLAG(a)))
            status = STATUS_BINARY;
        else if (diff(fp, file))
            status = STATUS_DIFFER;
    }
    if (status != STATUS_SAME)
        exit_status |= 1;
out:
    fclose_if_not_stdin(fp[0]);
    fclose_if_not_stdin(fp[1]);

    return status;
}

static void print_status(int status, char *path[2])
{
    switch (status) {
    case STATUS_BINARY:
    case STATUS_DIFFER:
        if ((option_mask32 & FLAG(q)) || status == STATUS_BINARY)
            printf("Files %s and %s differ\n", path[0], path[1]);
        break;
    case STATUS_SAME:
        if (option_mask32 & FLAG(s))
            printf("Files %s and %s are identical\n", path[0], path[1]);
        break;
    }
}

#if ENABLE_FEATURE_DIFF_DIR
struct dlist {
    size_t len;
    int s, e;
    char **dl;
};

/* 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)
{
    struct dlist *const l = userdata;
    const char *file = filename + l->len;
    while (*file == '/')
        file++;
    l->dl = xrealloc_vector(l->dl, 6, l->e);
    l->dl[l->e] = xstrdup(file);
    l->e++;
    return TRUE;
}

/* If recursion is not set, this function adds the directory
 * to the list and prevents recursive_action from recursing into it.
 */
static int FAST_FUNC skip_dir(const char *filename,
        struct stat *sb, void *userdata,
        int depth)
{
    if (!(option_mask32 & FLAG(r)) && depth) {
        add_to_dirlist(filename, sb, userdata, depth);
        return SKIP;
    }
    if (!(option_mask32 & FLAG(N))) {
        /* -r without -N: no need to recurse into dirs
         * which do not exist on the "other side".
         * Testcase: diff -r /tmp /
         * (it would recurse deep into /proc without this code) */
        struct dlist *const l = userdata;
        filename += l->len;
        if (filename[0]) {
            struct stat osb;
            char *othername = concat_path_file(G.other_dir, filename);
            int r = stat(othername, &osb);
            free(othername);
            if (r != 0 || !S_ISDIR(osb.st_mode)) {
                /* other dir doesn't have similarly named
                 * directory, don't recurse */
                return SKIP;
            }
        }
    }
    return TRUE;
}

static void diffdir(char *p[2], const char *s_start)
{
    struct dlist list[2];
    int i;

    memset(&list, 0, sizeof(list));
    for (i = 0; i < 2; i++) {
        /*list[i].s = list[i].e = 0; - memset did it */
        /*list[i].dl = NULL; */

        G.other_dir = p[1 - i];
        /* We need to trim root directory prefix.
         * Using list.len to specify its length,
         * add_to_dirlist will remove it. */
        list[i].len = strlen(p[i]);
        recursive_action(p[i], ACTION_RECURSE | ACTION_FOLLOWLINKS,
                         add_to_dirlist, skip_dir, &list[i], 0);
        /* Sort dl alphabetically.
         * GNU diff does this ignoring any number of trailing dots.
         * We don't, so for us dotted files almost always are
         * first on the list.
         */
        qsort_string_vector(list[i].dl, list[i].e);
        /* If -S was set, find the starting point. */
        if (!s_start)
            continue;
        while (list[i].s < list[i].e && strcmp(list[i].dl[list[i].s], s_start) < 0)
            list[i].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 (1) {
        char *dp[2];
        int pos;
        int k;

        dp[0] = list[0].s < list[0].e ? list[0].dl[list[0].s] : NULL;
        dp[1] = list[1].s < list[1].e ? list[1].dl[list[1].s] : NULL;
        if (!dp[0] && !dp[1])
            break;
        pos = !dp[0] ? 1 : (!dp[1] ? -1 : strcmp(dp[0], dp[1]));
        k = pos > 0;
        if (pos && !(option_mask32 & FLAG(N)))
            printf("Only in %s: %s\n", p[k], dp[k]);
        else {
            char *fullpath[2], *path[2]; /* if -N */

            for (i = 0; i < 2; i++) {
                if (pos == 0 || i == k) {
                    path[i] = fullpath[i] = concat_path_file(p[i], dp[i]);
                    stat(fullpath[i], &stb[i]);
                } else {
                    fullpath[i] = concat_path_file(p[i], dp[1 - i]);
                    path[i] = (char *)bb_dev_null;
                }
            }
            if (pos)
                stat(fullpath[k], &stb[1 - k]);

            if (S_ISDIR(stb[0].st_mode) && S_ISDIR(stb[1].st_mode))
                printf("Common subdirectories: %s and %s\n", fullpath[0], fullpath[1]);
            else if (!S_ISREG(stb[0].st_mode) && !S_ISDIR(stb[0].st_mode))
                printf("File %s is not a regular file or directory and was skipped\n", fullpath[0]);
            else if (!S_ISREG(stb[1].st_mode) && !S_ISDIR(stb[1].st_mode))
                printf("File %s is not a regular file or directory and was skipped\n", fullpath[1]);
            else if (S_ISDIR(stb[0].st_mode) != S_ISDIR(stb[1].st_mode)) {
                if (S_ISDIR(stb[0].st_mode))
                    printf("File %s is a %s while file %s is a %s\n", fullpath[0], "directory", fullpath[1], "regular file");
                else
                    printf("File %s is a %s while file %s is a %s\n", fullpath[0], "regular file", fullpath[1], "directory");
            } else
                print_status(diffreg(path), fullpath);

            free(fullpath[0]);
            free(fullpath[1]);
        }
        free(dp[k]);
        list[k].s++;
        if (pos == 0) {
            free(dp[1 - k]);
            list[1 - k].s++;
        }
    }
    if (ENABLE_FEATURE_CLEAN_UP) {
        free(list[0].dl);
        free(list[1].dl);
    }
}
#endif

#if ENABLE_FEATURE_DIFF_LONG_OPTIONS
static const char diff_longopts[] ALIGN1 =
    "ignore-case\0"              No_argument       "i"
    "ignore-tab-expansion\0"     No_argument       "E"
    "ignore-space-change\0"      No_argument       "b"
    "ignore-all-space\0"         No_argument       "w"
    "ignore-blank-lines\0"       No_argument       "B"
    "text\0"                     No_argument       "a"
    "unified\0"                  Required_argument "U"
    "label\0"                    Required_argument "L"
    "show-c-function\0"          No_argument       "p"
    "brief\0"                    No_argument       "q"
    "expand-tabs\0"              No_argument       "t"
    "initial-tab\0"              No_argument       "T"
    "recursive\0"                No_argument       "r"
    "new-file\0"                 No_argument       "N"
    "report-identical-files\0"   No_argument       "s"
    "starting-file\0"            Required_argument "S"
    "minimal\0"                  No_argument       "d"
    ;
#endif

int diff_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int diff_main(int argc UNUSED_PARAM, char **argv)
{
    int gotstdin = 0, i;
    char *file[2], *s_start = NULL;
    llist_t *L_arg = NULL;

    INIT_G();

    /* exactly 2 params; collect multiple -L <label>; -U N */
    opt_complementary = "=2:L::U+";
#if ENABLE_FEATURE_DIFF_LONG_OPTIONS
    applet_long_options = diff_longopts;
#endif
    getopt32(argv, "abdiL:NqrsS:tTU:wupBE",
            &L_arg, &s_start, &opt_U_context);
    argv += optind;
    while (L_arg)
        label[!!label[0]] = llist_pop(&L_arg);
    xfunc_error_retval = 2;
    for (i = 0; i < 2; i++) {
        file[i] = argv[i];
        /* Compat: "diff file name_which_doesnt_exist" exits with 2 */
        if (LONE_DASH(file[i])) {
            fstat(STDIN_FILENO, &stb[i]);
            gotstdin++;
        } else
            xstat(file[i], &stb[i]);
    }
    xfunc_error_retval = 1;
    if (gotstdin && (S_ISDIR(stb[0].st_mode) || S_ISDIR(stb[1].st_mode)))
        bb_error_msg_and_die("can't compare stdin to a directory");

    if (S_ISDIR(stb[0].st_mode) && S_ISDIR(stb[1].st_mode)) {
#if ENABLE_FEATURE_DIFF_DIR
        diffdir(file, s_start);
#else
        bb_error_msg_and_die("no support for directory comparison");
#endif
    } else {
        bool dirfile = S_ISDIR(stb[0].st_mode) || S_ISDIR(stb[1].st_mode);
        bool dir = S_ISDIR(stb[1].st_mode);
        if (dirfile) {
            const char *slash = strrchr(file[!dir], '/');
            file[dir] = concat_path_file(file[dir], slash ? slash + 1 : file[!dir]);
            xstat(file[dir], &stb[dir]);
        }
        /* diffreg can get non-regular files here */
        print_status(gotstdin > 1 ? STATUS_SAME : diffreg(file), file);

        if (dirfile)
            free(file[dir]);
    }

    return exit_status;
}