view mercurial/bdiff.c @ 1183:d9e85a75dbda

Optimize dirstate walking

This generally cuts the time for hg status/diff in half, from 2s down to 1s.
The main parts I'm trying to optimize are:

1) os.walk stats every file.  dirstate.changes then stats every file again.

2) os.walk yields every file and subdir to dirstate.traverse who yields every
file and everything in the dirstate map.  dirstate.walk then
filters this mass and yields every file to the caller.  There should be
fewer steps in here, and fewer duplicate strings yielded.

3) dirstate.walk runs util.unique on the results from dirstate.traverse,
even though it is also passing things through dirstate.seen to look for
duplicates.

I've turned os.walk into something hg specific that takes all the dirstate
ignore and matching rules into account.  The new function also takes an
function arg (statmatch()) the caller supplies to help filter out
files it doesn't care about.  dirstate.changes uses this to update state
for each file, avoiding the second stat call.

dirstate.walk is changed to turn the match function it is passed into
a statmatch function.  The only real difference is that a statmatch
function takes the stat data as a second parameter.  It now calls
dirstate.walkhelper, who requires a statmatch function to be passed.

This fails test-walk, but right now I think this is from a sorting error
fixed by this patch.

Index: crew/mercurial/dirstate.py
===================================================================

/*
 bdiff.c - efficient binary diff extension for Mercurial

 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.

 Based roughly on Python difflib
*/

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

#ifdef __hpux
#define inline
#endif

#ifdef _WIN32
#ifdef _MSC_VER
#define inline __inline
typedef unsigned long uint32_t;
#else
#include <stdint.h>
#endif
static uint32_t htonl(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

struct line {
	int h, len, n, e;
	const char *l;
};

struct pos {
	int pos, len;
};

struct hunk {
	int a1, a2, b1, b2;
};

struct hunklist {
	struct hunk *base, *head;
};

static __inline uint32_t rol32(uint32_t word, unsigned int shift)
{
        return (word << shift) | (word >> (32 - shift));
}

int splitlines(const char *a, int len, struct line **lr)
{
	int h, i;
	const char *p, *b = a;
	struct line *l;

	/* count the lines */
	i = 1; /* extra line for sentinel */
	for (p = a; p < a + len; p++)
		if (*p == '\n' || p == a + len - 1)
			i++;

	*lr = l = malloc(sizeof(struct line) * i);
	if (!l)
		return -1;

	/* build the line array and calculate hashes */
	h = 0;
	for (p = a; p < a + len; p++) {
		h = *p + rol32(h, 7); /* a simple hash from GNU diff */
		if (*p == '\n' || p == a + len - 1) {
			l->len = p - b + 1;
			l->h = h * l->len;
			l->l = b;
			l->n = -1;
			l++;
			b = p + 1;
			h = 0;
		}
	}

	/* set up a sentinel */
	l->h = l->len = 0;
	l->l = a + len;
	return i - 1;
}

int inline cmp(struct line *a, struct line *b)
{
	return a->h != b->h || a->len != b->len || memcmp(a->l, b->l, a->len);
}

static int equatelines(struct line *a, int an, struct line *b, int bn)
{
	int i, j, buckets = 1, t;
	struct pos *h;

	/* build a hash table of the next highest power of 2 */
	while (buckets < bn + 1)
		buckets *= 2;

	h = malloc(buckets * sizeof(struct pos));
	buckets = buckets - 1;
	if (!h)
		return 0;

	/* clear the hash table */
	for (i = 0; i <= buckets; i++) {
		h[i].pos = -1;
		h[i].len = 0;
	}

	/* add lines to the hash table chains */
	for (i = bn - 1; i >= 0; i--) {
		/* find the equivalence class */
		for (j = b[i].h & buckets; h[j].pos != -1;
		     j = (j + 1) & buckets)
			if (!cmp(b + i, b + h[j].pos))
				break;

		/* add to the head of the equivalence class */
		b[i].n = h[j].pos;
		b[i].e = j;
		h[j].pos = i;
		h[j].len++; /* keep track of popularity */
	}

	/* compute popularity threshold */
	t = (bn >= 200) ? bn / 100 : bn + 1;

	/* match items in a to their equivalence class in b */
	for (i = 0; i < an; i++) {
		/* find the equivalence class */
		for (j = a[i].h & buckets; h[j].pos != -1;
		     j = (j + 1) & buckets)
			if (!cmp(a + i, b + h[j].pos))
				break;

		a[i].e = j; /* use equivalence class for quick compare */
		if(h[j].len <= t)
			a[i].n = h[j].pos; /* point to head of match list */
		else
			a[i].n = -1; /* too popular */
	}

	/* discard hash tables */
	free(h);
	return 1;
}

static int longest_match(struct line *a, struct line *b, struct pos *pos,
			 int a1, int a2, int b1, int b2, int *omi, int *omj)
{
	int mi = a1, mj = b1, mk = 0, mb = 0, i, j, k;

	for (i = a1; i < a2; i++) {
		/* skip things before the current block */
		for (j = a[i].n; j != -1 && j < b1; j = b[j].n)
			;

		/* loop through all lines match a[i] in b */
		for (; j != -1 && j < b2; j = b[j].n) {
			/* does this extend an earlier match? */
			if (i > a1 && j > b1 && pos[j - 1].pos == i - 1)
				k = pos[j - 1].len + 1;
			else
				k = 1;
			pos[j].pos = i;
			pos[j].len = k;

			/* best match so far? */
			if (k > mk) {
				mi = i;
				mj = j;
				mk = k;
			}
		}
	}

	if (mk) {
		mi = mi - mk + 1;
		mj = mj - mk + 1;
	}

	/* expand match to include neighboring popular lines */
	while (mi - mb > a1 && mj - mb > b1 &&
	       a[mi - mb - 1].e == b[mj - mb - 1].e)
		mb++;
	while (mi + mk < a2 && mj + mk < b2 &&
	       a[mi + mk].e == b[mj + mk].e)
		mk++;

	*omi = mi - mb;
	*omj = mj - mb;
	return mk + mb;
}

static void recurse(struct line *a, struct line *b, struct pos *pos,
		    int a1, int a2, int b1, int b2, struct hunklist *l)
{
	int i, j, k;

	/* find the longest match in this chunk */
	k = longest_match(a, b, pos, a1, a2, b1, b2, &i, &j);
	if (!k)
		return;

	/* and recurse on the remaining chunks on either side */
	recurse(a, b, pos, a1, i, b1, j, l);
	l->head->a1 = i;
	l->head->a2 = i + k;
	l->head->b1 = j;
	l->head->b2 = j + k;
	l->head++;
	recurse(a, b, pos, i + k, a2, j + k, b2, l);
}

static struct hunklist diff(struct line *a, int an, struct line *b, int bn)
{
	struct hunklist l;
	struct pos *pos;
	int t;

	/* allocate and fill arrays */
	t = equatelines(a, an, b, bn);
	pos = calloc(bn, sizeof(struct pos));
	/* we can't have more matches than lines in the shorter file */
	l.head = l.base = malloc(sizeof(struct hunk) * ((an<bn ? an:bn) + 1));

	if (pos && l.base && t) {
		/* generate the matching block list */
		recurse(a, b, pos, 0, an, 0, bn, &l);
		l.head->a1 = an;
		l.head->b1 = bn;
		l.head++;
	}

	free(pos);
	return l;
}

static PyObject *blocks(PyObject *self, PyObject *args)
{
	PyObject *sa, *sb, *rl = NULL, *m;
	struct line *a, *b;
	struct hunklist l = {NULL, NULL};
	struct hunk *h;
	int an, bn, pos = 0;

	if (!PyArg_ParseTuple(args, "SS:bdiff", &sa, &sb))
		return NULL;

	an = splitlines(PyString_AsString(sa), PyString_Size(sa), &a);
	bn = splitlines(PyString_AsString(sb), PyString_Size(sb), &b);
	if (!a || !b)
		goto nomem;

	l = diff(a, an, b, bn);
	rl = PyList_New(l.head - l.base);
	if (!l.head || !rl)
		goto nomem;

	for(h = l.base; h != l.head; h++) {
		m = Py_BuildValue("iiii", h->a1, h->a2, h->b1, h->b2);
		PyList_SetItem(rl, pos, m);
		pos++;
	}

nomem:
	free(a);
	free(b);
	free(l.base);
	return rl ? rl : PyErr_NoMemory();
}

static PyObject *bdiff(PyObject *self, PyObject *args)
{
	PyObject *sa, *sb, *result = NULL;
	struct line *al, *bl;
	struct hunklist l = {NULL, NULL};
	struct hunk *h;
	char encode[12], *rb;
	int an, bn, len = 0, la = 0, lb = 0;

	if (!PyArg_ParseTuple(args, "SS:bdiff", &sa, &sb))
		return NULL;

	an = splitlines(PyString_AsString(sa), PyString_Size(sa), &al);
	bn = splitlines(PyString_AsString(sb), PyString_Size(sb), &bl);
	if (!al || !bl)
		goto nomem;

	l = diff(al, an, bl, bn);
	if (!l.head)
		goto nomem;

	/* calculate length of output */
	for(h = l.base; h != l.head; h++) {
		if (h->a1 != la || h->b1 != lb)
			len += 12 + bl[h->b1].l - bl[lb].l;
		la = h->a2;
		lb = h->b2;
	}

	result = PyString_FromStringAndSize(NULL, len);
	if (!result)
		goto nomem;

	/* build binary patch */
	rb = PyString_AsString(result);
	la = lb = 0;

	for(h = l.base; h != l.head; h++) {
		if (h->a1 != la || h->b1 != lb) {
			len = bl[h->b1].l - bl[lb].l;
			*(uint32_t *)(encode)     = htonl(al[la].l - al->l);
			*(uint32_t *)(encode + 4) = htonl(al[h->a1].l - al->l);
			*(uint32_t *)(encode + 8) = htonl(len);
			memcpy(rb, encode, 12);
			memcpy(rb + 12, bl[lb].l, len);
			rb += 12 + len;
		}
		la = h->a2;
		lb = h->b2;
	}

nomem:
	free(al);
	free(bl);
	free(l.base);
	return result ? result : PyErr_NoMemory();
}

static char mdiff_doc[] = "Efficient binary diff.";

static PyMethodDef methods[] = {
	{"bdiff", bdiff, METH_VARARGS, "calculate a binary diff\n"},
	{"blocks", blocks, METH_VARARGS, "find a list of matching lines\n"},
	{NULL, NULL}
};

PyMODINIT_FUNC initbdiff(void)
{
	Py_InitModule3("bdiff", methods, mdiff_doc);
}