mercurial/mpatch.c

patch: allow copy information to be passed in

When displaying patches from graphical tools where you can browse through
individual files, with diff being called separately on each, recomputing the
limits of file copy history can become rather expensive on large repositories.
Instead, we can compute it once and pass it in for subsequent calls.

/*
 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, 2006 Matt Mackall <[e-mail]>

 This software may be used and distributed according to the terms
 of the GNU General Public License, incorporated herein by reference.
*/

#define PY_SSIZE_T_CLEAN
#include <Python.h>
#include <stdlib.h>
#include <string.h>

#include "util.h"

static char mpatch_doc[] = "Efficient binary patching.";
static PyObject *mpatch_Error;

struct frag {
	int start, end, len;
	const char *data;
};

struct flist {
	struct frag *base, *head, *tail;
};

static struct flist *lalloc(Py_ssize_t size)
{
	struct flist *a = NULL;

	if (size < 1)
		size = 1;

	a = (struct flist *)malloc(sizeof(struct flist));
	if (a) {
		a->base = (struct frag *)malloc(sizeof(struct frag) * size);
		if (a->base) {
			a->head = a->tail = a->base;
			return a;
		}
		free(a);
		a = NULL;
	}
	if (!PyErr_Occurred())
		PyErr_NoMemory();
	return NULL;
}

static void lfree(struct flist *a)
{
	if (a) {
		free(a->base);
		free(a);
	}
}

static Py_ssize_t 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)
			break; /* 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;

			break;
		}
	}

	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)
			break;

		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;

			break;
		}
	}

	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 = NULL;
	struct frag *bh, *ct;
	int offset = 0, post;

	if (a && b)
		c = lalloc((lsize(a) + lsize(b)) * 2);

	if (c) {

		for (bh = b->head; bh != b->tail; bh++) {
			/* 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++;
			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(const char *bin, Py_ssize_t len)
{
	struct flist *l;
	struct frag *lt;
	int pos = 0;

	/* assume worst case size, we won't have many of these lists */
	l = lalloc(len / 12 + 1);
	if (!l)
		return NULL;

	lt = l->tail;

	while (pos >= 0 && pos < len) {
		lt->start = getbe32(bin + pos);
		lt->end = getbe32(bin + pos + 4);
		lt->len = getbe32(bin + pos + 8);
		lt->data = bin + pos + 12;
		pos += 12 + lt->len;
		if (lt->start > lt->end || lt->len < 0)
			break; /* sanity check */
		lt++;
	}

	if (pos != len) {
		if (!PyErr_Occurred())
			PyErr_SetString(mpatch_Error, "patch cannot be decoded");
		lfree(l);
		return NULL;
	}

	l->tail = lt;
	return l;
}

/* calculate the size of resultant text */
static Py_ssize_t calcsize(Py_ssize_t len, struct flist *l)
{
	Py_ssize_t outlen = 0, last = 0;
	struct frag *f = l->head;

	while (f != l->tail) {
		if (f->start < last || f->end > len) {
			if (!PyErr_Occurred())
				PyErr_SetString(mpatch_Error,
				                "invalid patch");
			return -1;
		}
		outlen += f->start - last;
		last = f->end;
		outlen += f->len;
		f++;
	}

	outlen += len - last;
	return outlen;
}

static int apply(char *buf, const char *orig, Py_ssize_t len, struct flist *l)
{
	struct frag *f = l->head;
	int last = 0;
	char *p = buf;

	while (f != l->tail) {
		if (f->start < last || f->end > len) {
			if (!PyErr_Occurred())
				PyErr_SetString(mpatch_Error,
				                "invalid patch");
			return 0;
		}
		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);
	return 1;
}

/* recursively generate a patch of all bins between start and end */
static struct flist *fold(PyObject *bins, Py_ssize_t start, Py_ssize_t end)
{
	Py_ssize_t len, blen;
	const char *buffer;

	if (start + 1 == end) {
		/* trivial case, output a decoded list */
		PyObject *tmp = PyList_GetItem(bins, start);
		if (!tmp)
			return NULL;
		if (PyObject_AsCharBuffer(tmp, &buffer, &blen))
			return NULL;
		return decode(buffer, blen);
	}

	/* 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;
	const char *in;
	char *out;
	Py_ssize_t len, outlen, inlen;

	if (!PyArg_ParseTuple(args, "OO:mpatch", &text, &bins))
		return NULL;

	len = PyList_Size(bins);
	if (!len) {
		/* nothing to do */
		Py_INCREF(text);
		return text;
	}

	if (PyObject_AsCharBuffer(text, &in, &inlen))
		return NULL;

	patch = fold(bins, 0, len);
	if (!patch)
		return NULL;

	outlen = calcsize(inlen, patch);
	if (outlen < 0) {
		result = NULL;
		goto cleanup;
	}
	result = PyBytes_FromStringAndSize(NULL, outlen);
	if (!result) {
		result = NULL;
		goto cleanup;
	}
	out = PyBytes_AsString(result);
	if (!apply(out, in, inlen, patch)) {
		Py_DECREF(result);
		result = NULL;
	}
cleanup:
	lfree(patch);
	return result;
}

/* calculate size of a patched file directly */
static PyObject *
patchedsize(PyObject *self, PyObject *args)
{
	long orig, start, end, len, outlen = 0, last = 0, pos = 0;
	Py_ssize_t patchlen;
	char *bin;

	if (!PyArg_ParseTuple(args, "ls#", &orig, &bin, &patchlen))
		return NULL;

	while (pos >= 0 && pos < patchlen) {
		start = getbe32(bin + pos);
		end = getbe32(bin + pos + 4);
		len = getbe32(bin + pos + 8);
		if (start > end)
			break; /* sanity check */
		pos += 12 + len;
		outlen += start - last;
		last = end;
		outlen += len;
	}

	if (pos != patchlen) {
		if (!PyErr_Occurred())
			PyErr_SetString(mpatch_Error, "patch cannot be decoded");
		return NULL;
	}

	outlen += orig - last;
	return Py_BuildValue("l", outlen);
}

static PyMethodDef methods[] = {
	{"patches", patches, METH_VARARGS, "apply a series of patches\n"},
	{"patchedsize", patchedsize, METH_VARARGS, "calculed patched size\n"},
	{NULL, NULL}
};

#ifdef IS_PY3K
static struct PyModuleDef mpatch_module = {
	PyModuleDef_HEAD_INIT,
	"mpatch",
	mpatch_doc,
	-1,
	methods
};

PyMODINIT_FUNC PyInit_mpatch(void)
{
	PyObject *m;

	m = PyModule_Create(&mpatch_module);
	if (m == NULL)
		return NULL;

	mpatch_Error = PyErr_NewException("mercurial.mpatch.mpatchError",
					  NULL, NULL);
	Py_INCREF(mpatch_Error);
	PyModule_AddObject(m, "mpatchError", mpatch_Error);

	return m;
}
#else
PyMODINIT_FUNC
initmpatch(void)
{
	Py_InitModule3("mpatch", methods, mpatch_doc);
	mpatch_Error = PyErr_NewException("mercurial.mpatch.mpatchError",
					  NULL, NULL);
}
#endif