view mercurial/bdiff.c @ 22196:23fe278bde43

largefiles: keep largefiles from colliding with normal one during linear merge

Before this patch, linear merging of modified or newly added largefile
causes unexpected result, if (1) largefile collides with same name
normal one in the target revision and (2) "local" largefile is chosen,
even though branch merging between such revisions doesn't.

Expected result of such linear merging is:

  (1) (not yet recorded) largefile is kept in the working directory
  (2) largefile is marked as (re-)"added"
  (3) colliding normal file is marked as "removed"

But actual result is:

  (1) largefile in the working directory is unlinked
  (2) largefile is marked as "normal" (so treated as "missing")
  (3) the dirstate entry for colliding normal file is just dropped

(1) is very serious, because there is no way to restore temporarily
modified largefiles.

(3) prevents the next commit from adding the manifest with correct
"removal of (normal) file" information for newly created changeset.

The root cause of this problem is putting "lfile" into "actions['r']"
in linear-merging case. At liner merging, "actions['r']" causes:

  - unlinking "target file" in the working directory, but "lfile" as
    "target file" is also largefile itself in this case

  - dropping the dirstate entry for target file

"actions['f']" (= "forget") does only the latter, and this is reason
why this patch doesn't choose putting "lfile" into it instead of
"actions['r']".

This patch newly introduces action "lfmr" (LargeFiles: Mark as
Removed) to mark colliding normal file as "removed" without unlinking
it.

This patch uses "hg debugdirstate" instead of "hg status" in test,
because:

  - choosing "local largefile" hides "removed" status of "remote
    normal file" in "hg status" output, and

  - "hg status" for "large2" in this case has another problem fixed in
    the subsequent patch

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

 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.

 Based roughly on Python difflib
*/

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

#include "util.h"

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

struct pos {
	int pos, len;
};

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

static int splitlines(const char *a, Py_ssize_t len, struct line **lr)
{
	unsigned hash;
	int i;
	const char *p, *b = a;
	const char * const plast = a + len - 1;
	struct line *l;

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

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

	/* build the line array and calculate hashes */
	hash = 0;
	for (p = a; p < a + len; p++) {
		/* Leonid Yuriev's hash */
		hash = (hash * 1664525) + (unsigned char)*p + 1013904223;

		if (*p == '\n' || p == plast) {
			l->hash = hash;
			hash = 0;
			l->len = p - b + 1;
			l->l = b;
			l->n = INT_MAX;
			l++;
			b = p + 1;
		}
	}

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

static inline int cmp(struct line *a, struct line *b)
{
	return a->hash != b->hash || 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, scale;
	struct pos *h = NULL;

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

	/* try to allocate a large hash table to avoid collisions */
	for (scale = 4; scale; scale /= 2) {
		h = (struct pos *)malloc(scale * buckets * sizeof(struct pos));
		if (h)
			break;
	}

	if (!h)
		return 0;

	buckets = buckets * scale - 1;

	/* clear the hash table */
	for (i = 0; i <= buckets; i++) {
		h[i].pos = INT_MAX;
		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].hash & buckets; h[j].pos != INT_MAX;
		     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 >= 31000) ? bn / 1000 : 1000000 / (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].hash & buckets; h[j].pos != INT_MAX;
		     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 = INT_MAX; /* 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 < b1; j = b[j].n)
			;

		/* loop through all lines match a[i] in b */
		for (; 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 struct hunk *recurse(struct line *a, struct line *b, struct pos *pos,
			    int a1, int a2, int b1, int b2, struct hunk *l)
{
	int i, j, k;

	while (1) {
		/* find the longest match in this chunk */
		k = longest_match(a, b, pos, a1, a2, b1, b2, &i, &j);
		if (!k)
			return l;

		/* and recurse on the remaining chunks on either side */
		l = recurse(a, b, pos, a1, i, b1, j, l);
		if (!l)
			return NULL;

		l->next = (struct hunk *)malloc(sizeof(struct hunk));
		if (!l->next)
			return NULL;

		l = l->next;
		l->a1 = i;
		l->a2 = i + k;
		l->b1 = j;
		l->b2 = j + k;
		l->next = NULL;

		/* tail-recursion didn't happen, so do equivalent iteration */
		a1 = i + k;
		b1 = j + k;
	}
}

static int diff(struct line *a, int an, struct line *b, int bn,
		 struct hunk *base)
{
	struct hunk *curr;
	struct pos *pos;
	int t, count = 0;

	/* allocate and fill arrays */
	t = equatelines(a, an, b, bn);
	pos = (struct pos *)calloc(bn ? bn : 1, sizeof(struct pos));

	if (pos && t) {
		/* generate the matching block list */

		curr = recurse(a, b, pos, 0, an, 0, bn, base);
		if (!curr)
			return -1;

		/* sentinel end hunk */
		curr->next = (struct hunk *)malloc(sizeof(struct hunk));
		if (!curr->next)
			return -1;
		curr = curr->next;
		curr->a1 = curr->a2 = an;
		curr->b1 = curr->b2 = bn;
		curr->next = NULL;
	}

	free(pos);

	/* normalize the hunk list, try to push each hunk towards the end */
	for (curr = base->next; curr; curr = curr->next) {
		struct hunk *next = curr->next;
		int shift = 0;

		if (!next)
			break;

		if (curr->a2 == next->a1)
			while (curr->a2 + shift < an && curr->b2 + shift < bn
			       && !cmp(a + curr->a2 + shift,
				       b + curr->b2 + shift))
				shift++;
		else if (curr->b2 == next->b1)
			while (curr->b2 + shift < bn && curr->a2 + shift < an
			       && !cmp(b + curr->b2 + shift,
				       a + curr->a2 + shift))
				shift++;
		if (!shift)
			continue;
		curr->b2 += shift;
		next->b1 += shift;
		curr->a2 += shift;
		next->a1 += shift;
	}

	for (curr = base->next; curr; curr = curr->next)
		count++;
	return count;
}

static void freehunks(struct hunk *l)
{
	struct hunk *n;
	for (; l; l = n) {
		n = l->next;
		free(l);
	}
}

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

	l.next = NULL;

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

	an = splitlines(PyBytes_AsString(sa), PyBytes_Size(sa), &a);
	bn = splitlines(PyBytes_AsString(sb), PyBytes_Size(sb), &b);

	if (!a || !b)
		goto nomem;

	count = diff(a, an, b, bn, &l);
	if (count < 0)
		goto nomem;

	rl = PyList_New(count);
	if (!rl)
		goto nomem;

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

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

static PyObject *bdiff(PyObject *self, PyObject *args)
{
	char *sa, *sb, *rb;
	PyObject *result = NULL;
	struct line *al, *bl;
	struct hunk l, *h;
	int an, bn, count;
	Py_ssize_t len = 0, la, lb;
	PyThreadState *_save;

	l.next = NULL;

	if (!PyArg_ParseTuple(args, "s#s#:bdiff", &sa, &la, &sb, &lb))
		return NULL;

	if (la > UINT_MAX || lb > UINT_MAX) {
		PyErr_SetString(PyExc_ValueError, "bdiff inputs too large");
		return NULL;
	}

	_save = PyEval_SaveThread();
	an = splitlines(sa, la, &al);
	bn = splitlines(sb, lb, &bl);
	if (!al || !bl)
		goto nomem;

	count = diff(al, an, bl, bn, &l);
	if (count < 0)
		goto nomem;

	/* calculate length of output */
	la = lb = 0;
	for (h = l.next; h; h = h->next) {
		if (h->a1 != la || h->b1 != lb)
			len += 12 + bl[h->b1].l - bl[lb].l;
		la = h->a2;
		lb = h->b2;
	}
	PyEval_RestoreThread(_save);
	_save = NULL;

	result = PyBytes_FromStringAndSize(NULL, len);

	if (!result)
		goto nomem;

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

	for (h = l.next; h; h = h->next) {
		if (h->a1 != la || h->b1 != lb) {
			len = bl[h->b1].l - bl[lb].l;
			putbe32((uint32_t)(al[la].l - al->l), rb);
			putbe32((uint32_t)(al[h->a1].l - al->l), rb + 4);
			putbe32((uint32_t)len, rb + 8);
			memcpy(rb + 12, bl[lb].l, len);
			rb += 12 + len;
		}
		la = h->a2;
		lb = h->b2;
	}

nomem:
	if (_save)
		PyEval_RestoreThread(_save);
	free(al);
	free(bl);
	freehunks(l.next);
	return result ? result : PyErr_NoMemory();
}

/*
 * If allws != 0, remove all whitespace (' ', \t and \r). Otherwise,
 * reduce whitespace sequences to a single space and trim remaining whitespace
 * from end of lines.
 */
static PyObject *fixws(PyObject *self, PyObject *args)
{
	PyObject *s, *result = NULL;
	char allws, c;
	const char *r;
	Py_ssize_t i, rlen, wlen = 0;
	char *w;

	if (!PyArg_ParseTuple(args, "Sb:fixws", &s, &allws))
		return NULL;
	r = PyBytes_AsString(s);
	rlen = PyBytes_Size(s);

	w = (char *)malloc(rlen ? rlen : 1);
	if (!w)
		goto nomem;

	for (i = 0; i != rlen; i++) {
		c = r[i];
		if (c == ' ' || c == '\t' || c == '\r') {
			if (!allws && (wlen == 0 || w[wlen - 1] != ' '))
				w[wlen++] = ' ';
		} else if (c == '\n' && !allws
			  && wlen > 0 && w[wlen - 1] == ' ') {
			w[wlen - 1] = '\n';
		} else {
			w[wlen++] = c;
		}
	}

	result = PyBytes_FromStringAndSize(w, wlen);

nomem:
	free(w);
	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"},
	{"fixws", fixws, METH_VARARGS, "normalize diff whitespaces\n"},
	{NULL, NULL}
};

#ifdef IS_PY3K
static struct PyModuleDef bdiff_module = {
	PyModuleDef_HEAD_INIT,
	"bdiff",
	mdiff_doc,
	-1,
	methods
};

PyMODINIT_FUNC PyInit_bdiff(void)
{
	return PyModule_Create(&bdiff_module);
}
#else
PyMODINIT_FUNC initbdiff(void)
{
	Py_InitModule3("bdiff", methods, mdiff_doc);
}
#endif