view mercurial/mpatch.c @ 1803:06e7447c7302

speed up hg log --patch

Changing dodiff to read the manifest/changelog for node1 before calling
repo.update allows us to take advantage of the revlog revision cache.

Before this patch and my previous "speed up hg log --debug" patch, when
using hg log -p to display three revisions (A, B and C), dodiff and
repo.changes would end up reading the manifests in this order:

 B A B A C B C B

With both patches, this order becomes:

 A A B B B B C C

(This considers only dodiff and repo.changes.  I'm not sure how other
parts of hg log enter the picture.)

The speed up will depend on the revisions being displayed.  (All
"before" times already have my previous "speed up hg log --debug" patch
applied.)

hg repo (tip = 414e81ae971f).  hg log -p
         before           after
real    0m50.981s       0m45.279s
user    0m47.930s       0m42.560s
sys     0m2.526s        0m2.523s
output size: 6917897 bytes

kernel repo (tip = 9d4e135960ed).  hg log -p -l64
         before           after
real    2m14.995s       1m45.025s
user    2m9.509s        1m33.900s
sys     0m3.663s        0m2.942s
output size: 31497621 bytes

same kernel repo.  hg log -p -l64 -r c84c2069592f:0
         before           after
real    1m48.045s       1m0.076s
user    1m44.094s       0m58.492s
sys     0m2.603s        0m1.103s
output size: 197983 bytes

c84c2069592f was the tip of a 10 day old kernel repo that I had lying
around and was where I first tested this patch.  For some weird
coincidence it's also a place where the patch makes a huge difference.

/*
 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 <[e-mail]>

 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>
#ifdef _WIN32
#ifdef _MSC_VER
#define inline __inline
typedef unsigned long uint32_t;
#else
#include <stdint.h>
#endif
static uint32_t ntohl(uint32_t x)
{
	return ((x & 0x000000ffUL) << 24) |
		((x & 0x0000ff00UL) <<  8) |
		((x & 0x00ff0000UL) >>  8) |
		((x & 0xff000000UL) >> 24);
}
#else
#include <sys/types.h>
#include <arpa/inet.h>
#endif

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

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

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

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

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

static void lfree(struct flist *a)
{
	if (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)
			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(char *bin, int len)
{
	struct flist *l;
	struct frag *lt;
	char *end = bin + len;
	char decode[12]; /* for dealing with alignment issues */

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

	lt = l->tail;

	while (bin < end) {
		memcpy(decode, bin, 12);
		lt->start = ntohl(*(uint32_t *)decode);
		lt->end = ntohl(*(uint32_t *)(decode + 4));
		lt->len = ntohl(*(uint32_t *)(decode + 8));
		lt->data = bin + 12;
		bin += 12 + lt->len;
		lt++;
	}

	if (bin != end) {
		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 int calcsize(int len, struct flist *l)
{
	int 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, char *orig, int 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, int start, int end)
{
	int len;

	if (start + 1 == end) {
		/* trivial case, output a decoded list */
		PyObject *tmp = PyList_GetItem(bins, start);
		if (!tmp)
			return NULL;
		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, "SO:mpatch", &text, &bins))
		return NULL;

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

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

	outlen = calcsize(PyString_Size(text), patch);
	if (outlen < 0) {
		result = NULL;
		goto cleanup;
	}
	result = PyString_FromStringAndSize(NULL, outlen);
	if (!result) {
		result = NULL;
		goto cleanup;
	}
	in = PyString_AsString(text);
	out = PyString_AsString(result);
	if (!apply(out, in, PyString_Size(text), patch)) {
		Py_DECREF(result);
		result = NULL;
	}
cleanup:
	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);
	mpatch_Error = PyErr_NewException("mpatch.mpatchError", NULL, NULL);
}