archive: handle commits with an empty tree

[git/jnareb-git.git] / xdiff / xdiffi.c

/*
 *  LibXDiff by Davide Libenzi ( File Differential Library )
 *  Copyright (C) 2003  Davide Libenzi
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 *  Davide Libenzi <davidel@xmailserver.org>
 *
 */

#include "xinclude.h"



#define XDL_MAX_COST_MIN 256
#define XDL_HEUR_MIN_COST 256
#define XDL_LINE_MAX (long)((1UL << (CHAR_BIT * sizeof(long) - 1)) - 1)
#define XDL_SNAKE_CNT 20
#define XDL_K_HEUR 4



typedef struct s_xdpsplit {
        long i1, i2;
        int min_lo, min_hi;
} xdpsplit_t;




static long xdl_split(unsigned long const *ha1, long off1, long lim1,
                      unsigned long const *ha2, long off2, long lim2,
                      long *kvdf, long *kvdb, int need_min, xdpsplit_t *spl,
                      xdalgoenv_t *xenv);
static xdchange_t *xdl_add_change(xdchange_t *xscr, long i1, long i2, long chg1, long chg2);





/*
 * See "An O(ND) Difference Algorithm and its Variations", by Eugene Myers.
 * Basically considers a "box" (off1, off2, lim1, lim2) and scan from both
 * the forward diagonal starting from (off1, off2) and the backward diagonal
 * starting from (lim1, lim2). If the K values on the same diagonal crosses
 * returns the furthest point of reach. We might end up having to expensive
 * cases using this algorithm is full, so a little bit of heuristic is needed
 * to cut the search and to return a suboptimal point.
 */
static long xdl_split(unsigned long const *ha1, long off1, long lim1,
                      unsigned long const *ha2, long off2, long lim2,
                      long *kvdf, long *kvdb, int need_min, xdpsplit_t *spl,
                      xdalgoenv_t *xenv) {
        long dmin = off1 - lim2, dmax = lim1 - off2;
        long fmid = off1 - off2, bmid = lim1 - lim2;
        long odd = (fmid - bmid) & 1;
        long fmin = fmid, fmax = fmid;
        long bmin = bmid, bmax = bmid;
        long ec, d, i1, i2, prev1, best, dd, v, k;

        /*
         * Set initial diagonal values for both forward and backward path.
         */
        kvdf[fmid] = off1;
        kvdb[bmid] = lim1;

        for (ec = 1;; ec++) {
                int got_snake = 0;

                /*
                 * We need to extent the diagonal "domain" by one. If the next
                 * values exits the box boundaries we need to change it in the
                 * opposite direction because (max - min) must be a power of two.
                 * Also we initialize the external K value to -1 so that we can
                 * avoid extra conditions check inside the core loop.
                 */
                if (fmin > dmin)
                        kvdf[--fmin - 1] = -1;
                else
                        ++fmin;
                if (fmax < dmax)
                        kvdf[++fmax + 1] = -1;
                else
                        --fmax;

                for (d = fmax; d >= fmin; d -= 2) {
                        if (kvdf[d - 1] >= kvdf[d + 1])
                                i1 = kvdf[d - 1] + 1;
                        else
                                i1 = kvdf[d + 1];
                        prev1 = i1;
                        i2 = i1 - d;
                        for (; i1 < lim1 && i2 < lim2 && ha1[i1] == ha2[i2]; i1++, i2++);
                        if (i1 - prev1 > xenv->snake_cnt)
                                got_snake = 1;
                        kvdf[d] = i1;
                        if (odd && bmin <= d && d <= bmax && kvdb[d] <= i1) {
                                spl->i1 = i1;
                                spl->i2 = i2;
                                spl->min_lo = spl->min_hi = 1;
                                return ec;
                        }
                }

                /*
                 * We need to extent the diagonal "domain" by one. If the next
                 * values exits the box boundaries we need to change it in the
                 * opposite direction because (max - min) must be a power of two.
                 * Also we initialize the external K value to -1 so that we can
                 * avoid extra conditions check inside the core loop.
                 */
                if (bmin > dmin)
                        kvdb[--bmin - 1] = XDL_LINE_MAX;
                else
                        ++bmin;
                if (bmax < dmax)
                        kvdb[++bmax + 1] = XDL_LINE_MAX;
                else
                        --bmax;

                for (d = bmax; d >= bmin; d -= 2) {
                        if (kvdb[d - 1] < kvdb[d + 1])
                                i1 = kvdb[d - 1];
                        else
                                i1 = kvdb[d + 1] - 1;
                        prev1 = i1;
                        i2 = i1 - d;
                        for (; i1 > off1 && i2 > off2 && ha1[i1 - 1] == ha2[i2 - 1]; i1--, i2--);
                        if (prev1 - i1 > xenv->snake_cnt)
                                got_snake = 1;
                        kvdb[d] = i1;
                        if (!odd && fmin <= d && d <= fmax && i1 <= kvdf[d]) {
                                spl->i1 = i1;
                                spl->i2 = i2;
                                spl->min_lo = spl->min_hi = 1;
                                return ec;
                        }
                }

                if (need_min)
                        continue;

                /*
                 * If the edit cost is above the heuristic trigger and if
                 * we got a good snake, we sample current diagonals to see
                 * if some of the, have reached an "interesting" path. Our
                 * measure is a function of the distance from the diagonal
                 * corner (i1 + i2) penalized with the distance from the
                 * mid diagonal itself. If this value is above the current
                 * edit cost times a magic factor (XDL_K_HEUR) we consider
                 * it interesting.
                 */
                if (got_snake && ec > xenv->heur_min) {
                        for (best = 0, d = fmax; d >= fmin; d -= 2) {
                                dd = d > fmid ? d - fmid: fmid - d;
                                i1 = kvdf[d];
                                i2 = i1 - d;
                                v = (i1 - off1) + (i2 - off2) - dd;

                                if (v > XDL_K_HEUR * ec && v > best &&
                                    off1 + xenv->snake_cnt <= i1 && i1 < lim1 &&
                                    off2 + xenv->snake_cnt <= i2 && i2 < lim2) {
                                        for (k = 1; ha1[i1 - k] == ha2[i2 - k]; k++)
                                                if (k == xenv->snake_cnt) {
                                                        best = v;
                                                        spl->i1 = i1;
                                                        spl->i2 = i2;
                                                        break;
                                                }
                                }
                        }
                        if (best > 0) {
                                spl->min_lo = 1;
                                spl->min_hi = 0;
                                return ec;
                        }

                        for (best = 0, d = bmax; d >= bmin; d -= 2) {
                                dd = d > bmid ? d - bmid: bmid - d;
                                i1 = kvdb[d];
                                i2 = i1 - d;
                                v = (lim1 - i1) + (lim2 - i2) - dd;

                                if (v > XDL_K_HEUR * ec && v > best &&
                                    off1 < i1 && i1 <= lim1 - xenv->snake_cnt &&
                                    off2 < i2 && i2 <= lim2 - xenv->snake_cnt) {
                                        for (k = 0; ha1[i1 + k] == ha2[i2 + k]; k++)
                                                if (k == xenv->snake_cnt - 1) {
                                                        best = v;
                                                        spl->i1 = i1;
                                                        spl->i2 = i2;
                                                        break;
                                                }
                                }
                        }
                        if (best > 0) {
                                spl->min_lo = 0;
                                spl->min_hi = 1;
                                return ec;
                        }
                }

                /*
                 * Enough is enough. We spent too much time here and now we collect
                 * the furthest reaching path using the (i1 + i2) measure.
                 */
                if (ec >= xenv->mxcost) {
                        long fbest, fbest1, bbest, bbest1;

                        fbest = fbest1 = -1;
                        for (d = fmax; d >= fmin; d -= 2) {
                                i1 = XDL_MIN(kvdf[d], lim1);
                                i2 = i1 - d;
                                if (lim2 < i2)
                                        i1 = lim2 + d, i2 = lim2;
                                if (fbest < i1 + i2) {
                                        fbest = i1 + i2;
                                        fbest1 = i1;
                                }
                        }

                        bbest = bbest1 = XDL_LINE_MAX;
                        for (d = bmax; d >= bmin; d -= 2) {
                                i1 = XDL_MAX(off1, kvdb[d]);
                                i2 = i1 - d;
                                if (i2 < off2)
                                        i1 = off2 + d, i2 = off2;
                                if (i1 + i2 < bbest) {
                                        bbest = i1 + i2;
                                        bbest1 = i1;
                                }
                        }

                        if ((lim1 + lim2) - bbest < fbest - (off1 + off2)) {
                                spl->i1 = fbest1;
                                spl->i2 = fbest - fbest1;
                                spl->min_lo = 1;
                                spl->min_hi = 0;
                        } else {
                                spl->i1 = bbest1;
                                spl->i2 = bbest - bbest1;
                                spl->min_lo = 0;
                                spl->min_hi = 1;
                        }
                        return ec;
                }
        }
}


/*
 * Rule: "Divide et Impera". Recursively split the box in sub-boxes by calling
 * the box splitting function. Note that the real job (marking changed lines)
 * is done in the two boundary reaching checks.
 */
int xdl_recs_cmp(diffdata_t *dd1, long off1, long lim1,
                 diffdata_t *dd2, long off2, long lim2,
                 long *kvdf, long *kvdb, int need_min, xdalgoenv_t *xenv) {
        unsigned long const *ha1 = dd1->ha, *ha2 = dd2->ha;

        /*
         * Shrink the box by walking through each diagonal snake (SW and NE).
         */
        for (; off1 < lim1 && off2 < lim2 && ha1[off1] == ha2[off2]; off1++, off2++);
        for (; off1 < lim1 && off2 < lim2 && ha1[lim1 - 1] == ha2[lim2 - 1]; lim1--, lim2--);

        /*
         * If one dimension is empty, then all records on the other one must
         * be obviously changed.
         */
        if (off1 == lim1) {
                char *rchg2 = dd2->rchg;
                long *rindex2 = dd2->rindex;

                for (; off2 < lim2; off2++)
                        rchg2[rindex2[off2]] = 1;
        } else if (off2 == lim2) {
                char *rchg1 = dd1->rchg;
                long *rindex1 = dd1->rindex;

                for (; off1 < lim1; off1++)
                        rchg1[rindex1[off1]] = 1;
        } else {
                xdpsplit_t spl;
                spl.i1 = spl.i2 = 0;

                /*
                 * Divide ...
                 */
                if (xdl_split(ha1, off1, lim1, ha2, off2, lim2, kvdf, kvdb,
                              need_min, &spl, xenv) < 0) {

                        return -1;
                }

                /*
                 * ... et Impera.
                 */
                if (xdl_recs_cmp(dd1, off1, spl.i1, dd2, off2, spl.i2,
                                 kvdf, kvdb, spl.min_lo, xenv) < 0 ||
                    xdl_recs_cmp(dd1, spl.i1, lim1, dd2, spl.i2, lim2,
                                 kvdf, kvdb, spl.min_hi, xenv) < 0) {

                        return -1;
                }
        }

        return 0;
}


int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
                xdfenv_t *xe) {
        long ndiags;
        long *kvd, *kvdf, *kvdb;
        xdalgoenv_t xenv;
        diffdata_t dd1, dd2;

        if (XDF_DIFF_ALG(xpp->flags) == XDF_PATIENCE_DIFF)
                return xdl_do_patience_diff(mf1, mf2, xpp, xe);

        if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF)
                return xdl_do_histogram_diff(mf1, mf2, xpp, xe);

        if (xdl_prepare_env(mf1, mf2, xpp, xe) < 0) {

                return -1;
        }

        /*
         * Allocate and setup K vectors to be used by the differential algorithm.
         * One is to store the forward path and one to store the backward path.
         */
        ndiags = xe->xdf1.nreff + xe->xdf2.nreff + 3;
        if (!(kvd = (long *) xdl_malloc((2 * ndiags + 2) * sizeof(long)))) {

                xdl_free_env(xe);
                return -1;
        }
        kvdf = kvd;
        kvdb = kvdf + ndiags;
        kvdf += xe->xdf2.nreff + 1;
        kvdb += xe->xdf2.nreff + 1;

        xenv.mxcost = xdl_bogosqrt(ndiags);
        if (xenv.mxcost < XDL_MAX_COST_MIN)
                xenv.mxcost = XDL_MAX_COST_MIN;
        xenv.snake_cnt = XDL_SNAKE_CNT;
        xenv.heur_min = XDL_HEUR_MIN_COST;

        dd1.nrec = xe->xdf1.nreff;
        dd1.ha = xe->xdf1.ha;
        dd1.rchg = xe->xdf1.rchg;
        dd1.rindex = xe->xdf1.rindex;
        dd2.nrec = xe->xdf2.nreff;
        dd2.ha = xe->xdf2.ha;
        dd2.rchg = xe->xdf2.rchg;
        dd2.rindex = xe->xdf2.rindex;

        if (xdl_recs_cmp(&dd1, 0, dd1.nrec, &dd2, 0, dd2.nrec,
                         kvdf, kvdb, (xpp->flags & XDF_NEED_MINIMAL) != 0, &xenv) < 0) {

                xdl_free(kvd);
                xdl_free_env(xe);
                return -1;
        }

        xdl_free(kvd);

        return 0;
}


static xdchange_t *xdl_add_change(xdchange_t *xscr, long i1, long i2, long chg1, long chg2) {
        xdchange_t *xch;

        if (!(xch = (xdchange_t *) xdl_malloc(sizeof(xdchange_t))))
                return NULL;

        xch->next = xscr;
        xch->i1 = i1;
        xch->i2 = i2;
        xch->chg1 = chg1;
        xch->chg2 = chg2;

        return xch;
}


int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
        long ix, ixo, ixs, ixref, grpsiz, nrec = xdf->nrec;
        char *rchg = xdf->rchg, *rchgo = xdfo->rchg;
        xrecord_t **recs = xdf->recs;

        /*
         * This is the same of what GNU diff does. Move back and forward
         * change groups for a consistent and pretty diff output. This also
         * helps in finding joinable change groups and reduce the diff size.
         */
        for (ix = ixo = 0;;) {
                /*
                 * Find the first changed line in the to-be-compacted file.
                 * We need to keep track of both indexes, so if we find a
                 * changed lines group on the other file, while scanning the
                 * to-be-compacted file, we need to skip it properly. Note
                 * that loops that are testing for changed lines on rchg* do
                 * not need index bounding since the array is prepared with
                 * a zero at position -1 and N.
                 */
                for (; ix < nrec && !rchg[ix]; ix++)
                        while (rchgo[ixo++]);
                if (ix == nrec)
                        break;

                /*
                 * Record the start of a changed-group in the to-be-compacted file
                 * and find the end of it, on both to-be-compacted and other file
                 * indexes (ix and ixo).
                 */
                ixs = ix;
                for (ix++; rchg[ix]; ix++);
                for (; rchgo[ixo]; ixo++);

                do {
                        grpsiz = ix - ixs;

                        /*
                         * If the line before the current change group, is equal to
                         * the last line of the current change group, shift backward
                         * the group.
                         */
                        while (ixs > 0 && recs[ixs - 1]->ha == recs[ix - 1]->ha &&
                               xdl_recmatch(recs[ixs - 1]->ptr, recs[ixs - 1]->size, recs[ix - 1]->ptr, recs[ix - 1]->size, flags)) {
                                rchg[--ixs] = 1;
                                rchg[--ix] = 0;

                                /*
                                 * This change might have joined two change groups,
                                 * so we try to take this scenario in account by moving
                                 * the start index accordingly (and so the other-file
                                 * end-of-group index).
                                 */
                                for (; rchg[ixs - 1]; ixs--);
                                while (rchgo[--ixo]);
                        }

                        /*
                         * Record the end-of-group position in case we are matched
                         * with a group of changes in the other file (that is, the
                         * change record before the end-of-group index in the other
                         * file is set).
                         */
                        ixref = rchgo[ixo - 1] ? ix: nrec;

                        /*
                         * If the first line of the current change group, is equal to
                         * the line next of the current change group, shift forward
                         * the group.
                         */
                        while (ix < nrec && recs[ixs]->ha == recs[ix]->ha &&
                               xdl_recmatch(recs[ixs]->ptr, recs[ixs]->size, recs[ix]->ptr, recs[ix]->size, flags)) {
                                rchg[ixs++] = 0;
                                rchg[ix++] = 1;

                                /*
                                 * This change might have joined two change groups,
                                 * so we try to take this scenario in account by moving
                                 * the start index accordingly (and so the other-file
                                 * end-of-group index). Keep tracking the reference
                                 * index in case we are shifting together with a
                                 * corresponding group of changes in the other file.
                                 */
                                for (; rchg[ix]; ix++);
                                while (rchgo[++ixo])
                                        ixref = ix;
                        }
                } while (grpsiz != ix - ixs);

                /*
                 * Try to move back the possibly merged group of changes, to match
                 * the recorded postion in the other file.
                 */
                while (ixref < ix) {
                        rchg[--ixs] = 1;
                        rchg[--ix] = 0;
                        while (rchgo[--ixo]);
                }
        }

        return 0;
}


int xdl_build_script(xdfenv_t *xe, xdchange_t **xscr) {
        xdchange_t *cscr = NULL, *xch;
        char *rchg1 = xe->xdf1.rchg, *rchg2 = xe->xdf2.rchg;
        long i1, i2, l1, l2;

        /*
         * Trivial. Collects "groups" of changes and creates an edit script.
         */
        for (i1 = xe->xdf1.nrec, i2 = xe->xdf2.nrec; i1 >= 0 || i2 >= 0; i1--, i2--)
                if (rchg1[i1 - 1] || rchg2[i2 - 1]) {
                        for (l1 = i1; rchg1[i1 - 1]; i1--);
                        for (l2 = i2; rchg2[i2 - 1]; i2--);

                        if (!(xch = xdl_add_change(cscr, i1, i2, l1 - i1, l2 - i2))) {
                                xdl_free_script(cscr);
                                return -1;
                        }
                        cscr = xch;
                }

        *xscr = cscr;

        return 0;
}


void xdl_free_script(xdchange_t *xscr) {
        xdchange_t *xch;

        while ((xch = xscr) != NULL) {
                xscr = xscr->next;
                xdl_free(xch);
        }
}

static int xdl_call_hunk_func(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
                              xdemitconf_t const *xecfg)
{
        xdchange_t *xch, *xche;

        for (xch = xscr; xch; xch = xche->next) {
                xche = xdl_get_hunk(xch, xecfg);
                if (xecfg->hunk_func(xch->i1, xche->i1 + xche->chg1 - xch->i1,
                                     xch->i2, xche->i2 + xche->chg2 - xch->i2,
                                     ecb->priv) < 0)
                        return -1;
        }
        return 0;
}

int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
             xdemitconf_t const *xecfg, xdemitcb_t *ecb) {
        xdchange_t *xscr;
        xdfenv_t xe;
        emit_func_t ef = xecfg->hunk_func ? xdl_call_hunk_func : xdl_emit_diff;

        if (xdl_do_diff(mf1, mf2, xpp, &xe) < 0) {

                return -1;
        }
        if (xdl_change_compact(&xe.xdf1, &xe.xdf2, xpp->flags) < 0 ||
            xdl_change_compact(&xe.xdf2, &xe.xdf1, xpp->flags) < 0 ||
            xdl_build_script(&xe, &xscr) < 0) {

                xdl_free_env(&xe);
                return -1;
        }
        if (xscr) {
                if (ef(&xe, xscr, ecb, xecfg) < 0) {

                        xdl_free_script(xscr);
                        xdl_free_env(&xe);
                        return -1;
                }
                xdl_free_script(xscr);
        }
        xdl_free_env(&xe);

        return 0;
}