diff --git a/mercurial/mpatch.c b/mercurial/mpatch.c
new file mode 100644
--- /dev/null
+++ b/mercurial/mpatch.c
@@ -0,0 +1,295 @@
+/*
+ mpatch.c - efficient binary patching for Mercurial
+
+ This implements a patch algorithm that's O(m + nlog n) where m is the
+ size of the output and n is the number of patches.
+
+ Given a list of binary patches, it unpacks each into a hunk list,
+ then combines the hunk lists with a treewise recursion to form a
+ single hunk list. This hunk list is then applied to the original
+ text.
+
+ The text (or binary) fragments are copied directly from their source
+ Python objects into a preallocated output string to avoid the
+ allocation of intermediate Python objects. Working memory is about 2x
+ the total number of hunks.
+
+ Copyright 2005 Matt Mackall <mpm@selenic.com>
+
+ This software may be used and distributed according to the terms
+ of the GNU General Public License, incorporated herein by reference.
+*/
+
+#include <Python.h>
+#include <stdlib.h>
+#include <string.h>
+#include <netinet/in.h>
+#include <sys/types.h>
+
+static char mpatch_doc[] = "Efficient binary patching.";
+
+struct frag {
+	int start, end, len;
+	char *data;
+};
+
+struct flist {
+	struct frag *base, *head, *tail;
+};
+
+static struct flist *lalloc(int size)
+{
+	struct flist *a;
+
+	a = malloc(sizeof(struct flist));
+	a->head = a->tail = a->base = malloc(sizeof(struct frag) * size);
+	return a;
+}
+
+static void lfree(struct flist *a)
+{
+	free(a->base);
+	free(a);
+}
+
+static int lsize(struct flist *a)
+{
+	return a->tail - a->head;
+}
+
+/* move hunks in source that are less cut to dest, compensating
+   for changes in offset. the last hunk may be split if necessary.
+*/
+static int gather(struct flist *dest, struct flist *src, int cut, int offset)
+{
+	struct frag *d = dest->tail, *s = src->head;
+	int postend, c, l;
+
+	while (s != src->tail) {
+		if (s->start + offset >= cut)
+			goto exit; /* we've gone far enough */
+
+		postend = offset + s->start + s->len;
+		if (postend <= cut) {
+			/* save this hunk */
+			offset += s->start + s->len - s->end;
+			*d++ = *s++;
+		}
+		else {
+			/* break up this hunk */
+			c = cut - offset;
+			if (s->end < c)
+				c = s->end;
+			l = cut - offset - s->start;
+			if (s->len < l)
+				l = s->len;
+
+			offset += s->start + l - c;
+
+			d->start = s->start;
+			d->end = c;
+			d->len = l;
+			d->data = s->data;
+			d++;
+			s->start = c;
+			s->len = s->len - l;
+			s->data = s->data + l;
+
+			goto exit;
+		}
+	}
+
+ exit:
+	dest->tail = d;
+	src->head = s;
+	return offset;
+}
+
+/* like gather, but with no output list */
+static int discard(struct flist *src, int cut, int offset)
+{
+	struct frag *s = src->head;
+	int postend, c, l;
+
+	while (s != src->tail) {
+		if (s->start + offset >= cut)
+			goto exit;
+
+		postend = offset + s->start + s->len;
+		if (postend <= cut) {
+			offset += s->start + s->len - s->end;
+			s++;
+		}
+		else {
+			c = cut - offset;
+			if (s->end < c)
+				c = s->end;
+			l = cut - offset - s->start;
+			if (s->len < l)
+				l = s->len;
+
+			offset += s->start + l - c;
+			s->start = c;
+			s->len = s->len - l;
+			s->data = s->data + l;
+
+			goto exit;
+		}
+	}
+
+ exit:
+	src->head = s;
+	return offset;
+}
+
+/* combine hunk lists a and b, while adjusting b for offset changes in a/
+   this deletes a and b and returns the resultant list. */
+static struct flist *combine(struct flist *a, struct flist *b)
+{
+	struct flist *c;
+	struct frag *bh = b->head, *ct;
+	int offset = 0, post;
+
+	c = lalloc((lsize(a) + lsize(b)) * 2);
+
+	while (bh != b->tail) {
+		/* save old hunks */
+		offset = gather(c, a, bh->start, offset);
+
+		/* discard replaced hunks */
+		post = discard(a, bh->end, offset);
+
+		/* insert new hunk */
+		ct = c->tail;
+		ct->start = bh->start - offset;
+		ct->end = bh->end - post;
+		ct->len = bh->len;
+		ct->data = bh->data;
+		c->tail++;
+		bh++;
+		offset = post;
+	}
+
+	/* hold on to tail from a */
+	memcpy(c->tail, a->head, sizeof(struct frag) * lsize(a));
+	c->tail += lsize(a);
+	lfree(a);
+	lfree(b);
+	return c;
+}
+
+/* decode a binary patch into a hunk list */
+static struct flist *decode(char *bin, int len)
+{
+	struct flist *l;
+	struct frag *lt;
+	char *end = bin + len;
+
+	/* assume worst case size, we won't have many of these lists */
+	l = lalloc(len / 12);
+	lt = l->tail;
+
+	while (bin < end) {
+		lt->start = ntohl(*(uint32_t *)bin);
+		lt->end = ntohl(*(uint32_t *)(bin + 4));
+		lt->len = ntohl(*(uint32_t *)(bin + 8));
+		lt->data = bin + 12;
+		bin += 12 + lt->len;
+		lt++;
+	}
+
+	l->tail = lt;
+	return l;
+}
+
+/* calculate the size of resultant text */
+static int calcsize(int len, struct flist *l)
+{
+	int outlen = 0, last = 0;
+	struct frag *f = l->head;
+
+	while (f != l->tail) {
+		outlen += f->start - last;
+		last = f->end;
+		outlen += f->len;
+		f++;
+	}
+
+	outlen += len - last;
+	return outlen;
+}
+
+static void apply(char *buf, char *orig, int len, struct flist *l)
+{
+	struct frag *f = l->head;
+	int last = 0;
+	char *p = buf;
+
+	while (f != l->tail) {
+		memcpy(p, orig + last, f->start - last);
+		p += f->start - last;
+		memcpy(p, f->data, f->len);
+		last = f->end;
+		p += f->len;
+		f++;
+	}
+	memcpy(p, orig + last, len - last);
+}
+
+/* recursively generate a patch of all bins between start and end */
+static struct flist *fold(PyObject *bins, int start, int end)
+{
+	int len;
+
+	if (start + 1 == end) {
+		/* trivial case, output a decoded list */
+		PyObject *tmp = PyList_GetItem(bins, start);
+		return decode(PyString_AsString(tmp), PyString_Size(tmp));
+	}
+
+	/* divide and conquer, memory management is elsewhere */
+	len = (end - start) / 2;
+	return combine(fold(bins, start, start + len),
+		       fold(bins, start + len, end));
+}
+
+static PyObject *
+patches(PyObject *self, PyObject *args)
+{
+	PyObject *text, *bins, *result;
+	struct flist *patch;
+	char *in, *out;
+	int len, outlen;
+
+	if (!PyArg_ParseTuple(args, "OO:mpatch", &text, &bins))
+		return NULL;
+
+	len = PyList_Size(bins);
+	if (!len) {
+		/* nothing to do */
+		Py_INCREF(text);
+		return text;
+	}
+
+	patch = fold(bins, 0, len);
+	outlen = calcsize(PyString_Size(text), patch);
+	result = PyString_FromStringAndSize(NULL, outlen);
+	in = PyString_AsString(text);
+	out = PyString_AsString(result);
+	apply(out, in, PyString_Size(text), patch);
+	lfree(patch);
+
+	return result;
+}
+
+static PyMethodDef methods[] = {
+	{"patches", patches, METH_VARARGS, "apply a series of patches\n"},
+	{NULL, NULL}
+};
+
+PyMODINIT_FUNC
+initmpatch(void)
+{
+	Py_InitModule3("mpatch", methods, mpatch_doc);
+}
+