diff --git a/src/xdiff/xprepare.c b/src/xdiff/xprepare.c
new file mode 100644
index 0000000..abeb8fb
--- /dev/null
+++ b/src/xdiff/xprepare.c
@@ -0,0 +1,483 @@
+/*
+ *  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, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#include "xinclude.h"
+
+
+#define XDL_KPDIS_RUN 4
+#define XDL_MAX_EQLIMIT 1024
+#define XDL_SIMSCAN_WINDOW 100
+#define XDL_GUESS_NLINES1 256
+#define XDL_GUESS_NLINES2 20
+
+
+typedef struct s_xdlclass {
+	struct s_xdlclass *next;
+	unsigned long ha;
+	char const *line;
+	long size;
+	long idx;
+	long len1, len2;
+} xdlclass_t;
+
+typedef struct s_xdlclassifier {
+	unsigned int hbits;
+	long hsize;
+	xdlclass_t **rchash;
+	chastore_t ncha;
+	xdlclass_t **rcrecs;
+	long alloc;
+	long count;
+	long flags;
+} xdlclassifier_t;
+
+
+
+
+static int xdl_init_classifier(xdlclassifier_t *cf, long size, long flags);
+static void xdl_free_classifier(xdlclassifier_t *cf);
+static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t **rhash,
+			       unsigned int hbits, xrecord_t *rec);
+static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_t const *xpp,
+			   xdlclassifier_t *cf, xdfile_t *xdf);
+static void xdl_free_ctx(xdfile_t *xdf);
+static int xdl_clean_mmatch(char const *dis, long i, long s, long e);
+static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2);
+static int xdl_trim_ends(xdfile_t *xdf1, xdfile_t *xdf2);
+static int xdl_optimize_ctxs(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2);
+
+
+
+
+static int xdl_init_classifier(xdlclassifier_t *cf, long size, long flags) {
+	cf->flags = flags;
+
+	cf->hbits = xdl_hashbits((unsigned int) size);
+	cf->hsize = 1 << cf->hbits;
+
+	if (xdl_cha_init(&cf->ncha, sizeof(xdlclass_t), size / 4 + 1) < 0) {
+
+		return -1;
+	}
+	if (!(cf->rchash = (xdlclass_t **) xdl_malloc(cf->hsize * sizeof(xdlclass_t *)))) {
+
+		xdl_cha_free(&cf->ncha);
+		return -1;
+	}
+	memset(cf->rchash, 0, cf->hsize * sizeof(xdlclass_t *));
+
+	cf->alloc = size;
+	if (!(cf->rcrecs = (xdlclass_t **) xdl_malloc(cf->alloc * sizeof(xdlclass_t *)))) {
+
+		xdl_free(cf->rchash);
+		xdl_cha_free(&cf->ncha);
+		return -1;
+	}
+
+	cf->count = 0;
+
+	return 0;
+}
+
+
+static void xdl_free_classifier(xdlclassifier_t *cf) {
+
+	xdl_free(cf->rcrecs);
+	xdl_free(cf->rchash);
+	xdl_cha_free(&cf->ncha);
+}
+
+
+static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t **rhash,
+			       unsigned int hbits, xrecord_t *rec) {
+	long hi;
+	char const *line;
+	xdlclass_t *rcrec;
+	xdlclass_t **rcrecs;
+
+	line = rec->ptr;
+	hi = (long) XDL_HASHLONG(rec->ha, cf->hbits);
+	for (rcrec = cf->rchash[hi]; rcrec; rcrec = rcrec->next)
+		if (rcrec->ha == rec->ha &&
+				xdl_recmatch(rcrec->line, rcrec->size,
+					rec->ptr, rec->size, cf->flags))
+			break;
+
+	if (!rcrec) {
+		if (!(rcrec = xdl_cha_alloc(&cf->ncha))) {
+
+			return -1;
+		}
+		rcrec->idx = cf->count++;
+		if (cf->count > cf->alloc) {
+			cf->alloc *= 2;
+			if (!(rcrecs = (xdlclass_t **) xdl_realloc(cf->rcrecs, cf->alloc * sizeof(xdlclass_t *)))) {
+
+				return -1;
+			}
+			cf->rcrecs = rcrecs;
+		}
+		cf->rcrecs[rcrec->idx] = rcrec;
+		rcrec->line = line;
+		rcrec->size = rec->size;
+		rcrec->ha = rec->ha;
+		rcrec->len1 = rcrec->len2 = 0;
+		rcrec->next = cf->rchash[hi];
+		cf->rchash[hi] = rcrec;
+	}
+
+	(pass == 1) ? rcrec->len1++ : rcrec->len2++;
+
+	rec->ha = (unsigned long) rcrec->idx;
+
+	hi = (long) XDL_HASHLONG(rec->ha, hbits);
+	rec->next = rhash[hi];
+	rhash[hi] = rec;
+
+	return 0;
+}
+
+
+static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_t const *xpp,
+			   xdlclassifier_t *cf, xdfile_t *xdf) {
+	unsigned int hbits;
+	long nrec, hsize, bsize;
+	unsigned long hav;
+	char const *blk, *cur, *top, *prev;
+	xrecord_t *crec;
+	xrecord_t **recs, **rrecs;
+	xrecord_t **rhash;
+	unsigned long *ha;
+	char *rchg;
+	long *rindex;
+
+	ha = NULL;
+	rindex = NULL;
+	rchg = NULL;
+	rhash = NULL;
+	recs = NULL;
+
+	if (xdl_cha_init(&xdf->rcha, sizeof(xrecord_t), narec / 4 + 1) < 0)
+		goto abort;
+	if (!(recs = (xrecord_t **) xdl_malloc(narec * sizeof(xrecord_t *))))
+		goto abort;
+
+	if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF)
+		hbits = hsize = 0;
+	else {
+		hbits = xdl_hashbits((unsigned int) narec);
+		hsize = 1 << hbits;
+		if (!(rhash = (xrecord_t **) xdl_malloc(hsize * sizeof(xrecord_t *))))
+			goto abort;
+		memset(rhash, 0, hsize * sizeof(xrecord_t *));
+	}
+
+	nrec = 0;
+	if ((cur = blk = xdl_mmfile_first(mf, &bsize)) != NULL) {
+		for (top = blk + bsize; cur < top; ) {
+			prev = cur;
+			hav = xdl_hash_record(&cur, top, xpp->flags);
+			if (nrec >= narec) {
+				narec *= 2;
+				if (!(rrecs = (xrecord_t **) xdl_realloc(recs, narec * sizeof(xrecord_t *))))
+					goto abort;
+				recs = rrecs;
+			}
+			if (!(crec = xdl_cha_alloc(&xdf->rcha)))
+				goto abort;
+			crec->ptr = prev;
+			crec->size = (long) (cur - prev);
+			crec->ha = hav;
+			recs[nrec++] = crec;
+
+			if ((XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF) &&
+			    xdl_classify_record(pass, cf, rhash, hbits, crec) < 0)
+				goto abort;
+		}
+	}
+
+	if (!(rchg = (char *) xdl_malloc((nrec + 2) * sizeof(char))))
+		goto abort;
+	memset(rchg, 0, (nrec + 2) * sizeof(char));
+
+	if (!(rindex = (long *) xdl_malloc((nrec + 1) * sizeof(long))))
+		goto abort;
+	if (!(ha = (unsigned long *) xdl_malloc((nrec + 1) * sizeof(unsigned long))))
+		goto abort;
+
+	xdf->nrec = nrec;
+	xdf->recs = recs;
+	xdf->hbits = hbits;
+	xdf->rhash = rhash;
+	xdf->rchg = rchg + 1;
+	xdf->rindex = rindex;
+	xdf->nreff = 0;
+	xdf->ha = ha;
+	xdf->dstart = 0;
+	xdf->dend = nrec - 1;
+
+	return 0;
+
+abort:
+	xdl_free(ha);
+	xdl_free(rindex);
+	xdl_free(rchg);
+	xdl_free(rhash);
+	xdl_free(recs);
+	xdl_cha_free(&xdf->rcha);
+	return -1;
+}
+
+
+static void xdl_free_ctx(xdfile_t *xdf) {
+
+	xdl_free(xdf->rhash);
+	xdl_free(xdf->rindex);
+	xdl_free(xdf->rchg - 1);
+	xdl_free(xdf->ha);
+	xdl_free(xdf->recs);
+	xdl_cha_free(&xdf->rcha);
+}
+
+
+int xdl_prepare_env(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		    xdfenv_t *xe) {
+	long enl1, enl2, sample;
+	xdlclassifier_t cf;
+
+	memset(&cf, 0, sizeof(cf));
+
+	/*
+	 * For histogram diff, we can afford a smaller sample size and
+	 * thus a poorer estimate of the number of lines, as the hash
+	 * table (rhash) won't be filled up/grown. The number of lines
+	 * (nrecs) will be updated correctly anyway by
+	 * xdl_prepare_ctx().
+	 */
+	sample = (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF
+		  ? XDL_GUESS_NLINES2 : XDL_GUESS_NLINES1);
+
+	enl1 = xdl_guess_lines(mf1, sample) + 1;
+	enl2 = xdl_guess_lines(mf2, sample) + 1;
+
+	if (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF &&
+	    xdl_init_classifier(&cf, enl1 + enl2 + 1, xpp->flags) < 0)
+		return -1;
+
+	if (xdl_prepare_ctx(1, mf1, enl1, xpp, &cf, &xe->xdf1) < 0) {
+
+		xdl_free_classifier(&cf);
+		return -1;
+	}
+	if (xdl_prepare_ctx(2, mf2, enl2, xpp, &cf, &xe->xdf2) < 0) {
+
+		xdl_free_ctx(&xe->xdf1);
+		xdl_free_classifier(&cf);
+		return -1;
+	}
+
+	if ((XDF_DIFF_ALG(xpp->flags) != XDF_PATIENCE_DIFF) &&
+	    (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF) &&
+	    xdl_optimize_ctxs(&cf, &xe->xdf1, &xe->xdf2) < 0) {
+
+		xdl_free_ctx(&xe->xdf2);
+		xdl_free_ctx(&xe->xdf1);
+		xdl_free_classifier(&cf);
+		return -1;
+	}
+
+	if (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF)
+		xdl_free_classifier(&cf);
+
+	return 0;
+}
+
+
+void xdl_free_env(xdfenv_t *xe) {
+
+	xdl_free_ctx(&xe->xdf2);
+	xdl_free_ctx(&xe->xdf1);
+}
+
+
+static int xdl_clean_mmatch(char const *dis, long i, long s, long e) {
+	long r, rdis0, rpdis0, rdis1, rpdis1;
+
+	/*
+	 * Limits the window the is examined during the similar-lines
+	 * scan. The loops below stops when dis[i - r] == 1 (line that
+	 * has no match), but there are corner cases where the loop
+	 * proceed all the way to the extremities by causing huge
+	 * performance penalties in case of big files.
+	 */
+	if (i - s > XDL_SIMSCAN_WINDOW)
+		s = i - XDL_SIMSCAN_WINDOW;
+	if (e - i > XDL_SIMSCAN_WINDOW)
+		e = i + XDL_SIMSCAN_WINDOW;
+
+	/*
+	 * Scans the lines before 'i' to find a run of lines that either
+	 * have no match (dis[j] == 0) or have multiple matches (dis[j] > 1).
+	 * Note that we always call this function with dis[i] > 1, so the
+	 * current line (i) is already a multimatch line.
+	 */
+	for (r = 1, rdis0 = 0, rpdis0 = 1; (i - r) >= s; r++) {
+		if (!dis[i - r])
+			rdis0++;
+		else if (dis[i - r] == 2)
+			rpdis0++;
+		else
+			break;
+	}
+	/*
+	 * If the run before the line 'i' found only multimatch lines, we
+	 * return 0 and hence we don't make the current line (i) discarded.
+	 * We want to discard multimatch lines only when they appear in the
+	 * middle of runs with nomatch lines (dis[j] == 0).
+	 */
+	if (rdis0 == 0)
+		return 0;
+	for (r = 1, rdis1 = 0, rpdis1 = 1; (i + r) <= e; r++) {
+		if (!dis[i + r])
+			rdis1++;
+		else if (dis[i + r] == 2)
+			rpdis1++;
+		else
+			break;
+	}
+	/*
+	 * If the run after the line 'i' found only multimatch lines, we
+	 * return 0 and hence we don't make the current line (i) discarded.
+	 */
+	if (rdis1 == 0)
+		return 0;
+	rdis1 += rdis0;
+	rpdis1 += rpdis0;
+
+	return rpdis1 * XDL_KPDIS_RUN < (rpdis1 + rdis1);
+}
+
+
+/*
+ * Try to reduce the problem complexity, discard records that have no
+ * matches on the other file. Also, lines that have multiple matches
+ * might be potentially discarded if they happear in a run of discardable.
+ */
+static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2) {
+	long i, nm, nreff, mlim;
+	xrecord_t **recs;
+	xdlclass_t *rcrec;
+	char *dis, *dis1, *dis2;
+
+	if (!(dis = (char *) xdl_malloc(xdf1->nrec + xdf2->nrec + 2))) {
+
+		return -1;
+	}
+	memset(dis, 0, xdf1->nrec + xdf2->nrec + 2);
+	dis1 = dis;
+	dis2 = dis1 + xdf1->nrec + 1;
+
+	if ((mlim = xdl_bogosqrt(xdf1->nrec)) > XDL_MAX_EQLIMIT)
+		mlim = XDL_MAX_EQLIMIT;
+	for (i = xdf1->dstart, recs = &xdf1->recs[xdf1->dstart]; i <= xdf1->dend; i++, recs++) {
+		rcrec = cf->rcrecs[(*recs)->ha];
+		nm = rcrec ? rcrec->len2 : 0;
+		dis1[i] = (nm == 0) ? 0: (nm >= mlim) ? 2: 1;
+	}
+
+	if ((mlim = xdl_bogosqrt(xdf2->nrec)) > XDL_MAX_EQLIMIT)
+		mlim = XDL_MAX_EQLIMIT;
+	for (i = xdf2->dstart, recs = &xdf2->recs[xdf2->dstart]; i <= xdf2->dend; i++, recs++) {
+		rcrec = cf->rcrecs[(*recs)->ha];
+		nm = rcrec ? rcrec->len1 : 0;
+		dis2[i] = (nm == 0) ? 0: (nm >= mlim) ? 2: 1;
+	}
+
+	for (nreff = 0, i = xdf1->dstart, recs = &xdf1->recs[xdf1->dstart];
+	     i <= xdf1->dend; i++, recs++) {
+		if (dis1[i] == 1 ||
+		    (dis1[i] == 2 && !xdl_clean_mmatch(dis1, i, xdf1->dstart, xdf1->dend))) {
+			xdf1->rindex[nreff] = i;
+			xdf1->ha[nreff] = (*recs)->ha;
+			nreff++;
+		} else
+			xdf1->rchg[i] = 1;
+	}
+	xdf1->nreff = nreff;
+
+	for (nreff = 0, i = xdf2->dstart, recs = &xdf2->recs[xdf2->dstart];
+	     i <= xdf2->dend; i++, recs++) {
+		if (dis2[i] == 1 ||
+		    (dis2[i] == 2 && !xdl_clean_mmatch(dis2, i, xdf2->dstart, xdf2->dend))) {
+			xdf2->rindex[nreff] = i;
+			xdf2->ha[nreff] = (*recs)->ha;
+			nreff++;
+		} else
+			xdf2->rchg[i] = 1;
+	}
+	xdf2->nreff = nreff;
+
+	xdl_free(dis);
+
+	return 0;
+}
+
+
+/*
+ * Early trim initial and terminal matching records.
+ */
+static int xdl_trim_ends(xdfile_t *xdf1, xdfile_t *xdf2) {
+	long i, lim;
+	xrecord_t **recs1, **recs2;
+
+	recs1 = xdf1->recs;
+	recs2 = xdf2->recs;
+	for (i = 0, lim = XDL_MIN(xdf1->nrec, xdf2->nrec); i < lim;
+	     i++, recs1++, recs2++)
+		if ((*recs1)->ha != (*recs2)->ha)
+			break;
+
+	xdf1->dstart = xdf2->dstart = i;
+
+	recs1 = xdf1->recs + xdf1->nrec - 1;
+	recs2 = xdf2->recs + xdf2->nrec - 1;
+	for (lim -= i, i = 0; i < lim; i++, recs1--, recs2--)
+		if ((*recs1)->ha != (*recs2)->ha)
+			break;
+
+	xdf1->dend = xdf1->nrec - i - 1;
+	xdf2->dend = xdf2->nrec - i - 1;
+
+	return 0;
+}
+
+
+static int xdl_optimize_ctxs(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2) {
+
+	if (xdl_trim_ends(xdf1, xdf2) < 0 ||
+	    xdl_cleanup_records(cf, xdf1, xdf2) < 0) {
+
+		return -1;
+	}
+
+	return 0;
+}