comparison mercurial/thirdparty/xdiff/xutils.c @ 36671:34e2ff1f9cd8

xdiff: vendor xdiff library from git

Vendor git's xdiff library from git commit
d7c6c2369d7c6c2369ac21141b7c6cceaebc6414ec3da14ad using GPL2+ license.

There is another recent user report that hg diff generates suboptimal
result. It seems the fix to issue4074 isn't good enough. I crafted some
other interesting cases, and hg diff barely has any advantage compared with
gnu diffutils or git diff.

| testcase | gnu diffutils |      hg diff |   git diff |
|          |    lines time |   lines time | lines time |
| patience |        6 0.00 |     602 0.08 |     6 0.00 |
|   random |    91772 0.90 |  109462 0.70 | 91772 0.24 |
|     json |        2 0.03 | 1264814 1.81 |     2 0.29 |

"lines" means the size of the output, i.e. the count of "+/-" lines. "time"
means seconds needed to do the calculation. Both are the smaller the better.
"hg diff" counts Python startup overhead.

Git and GNU diffutils generate optimal results. For the "json" case, git can
have an optimization that does a scan for common prefix and suffix first,
and match them if the length is greater than half of the text. See
https://neil.fraser.name/news/2006/03/12/. That would make git the fastest
for all above cases.

About testcases:

patience:
Aiming for the weakness of the greedy "patience diff" algorithm.  Using
git's patience diff option would also get suboptimal result. Generated using
the Python script:

```
open('a', 'w').write('\n'.join(list('a' + 'x' * 300 + 'u' + 'x' * 700 + 'a\n')))
open('b', 'w').write('\n'.join(list('b' + 'x' * 700 + 'u' + 'x' * 300 + 'b\n')))
```

random:
Generated using the script in `test-issue4074.t`. It practically makes the
algorithm suffer. Impressively, git wins in both performance and diff
quality.

json:
The recent user reported case. It's a single line movement near the end of a
very large (800K lines) JSON file.

Test Plan:
Code taken as-is.

Differential Revision: https://phab.mercurial-scm.org/D2572

# no-check-commit for vendored code

36671:34e2ff1f9cd8

/*
 *  LibXDiff by Davide Libenzi ( File Differential Library )
 *  Copyright (C) 2003	Davide Libenzi
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, see
 *  <http://www.gnu.org/licenses/>.
 *
 *  Davide Libenzi <[e-mail]>
 *
 */

#include <limits.h>
#include <assert.h>
#include "xinclude.h"




long xdl_bogosqrt(long n) {
	long i;

	/*
	 * Classical integer square root approximation using shifts.
	 */
	for (i = 1; n > 0; n >>= 2)
		i <<= 1;

	return i;
}


int xdl_emit_diffrec(char const *rec, long size, char const *pre, long psize,
		     xdemitcb_t *ecb) {
	int i = 2;
	mmbuffer_t mb[3];

	mb[0].ptr = (char *) pre;
	mb[0].size = psize;
	mb[1].ptr = (char *) rec;
	mb[1].size = size;
	if (size > 0 && rec[size - 1] != '\n') {
		mb[2].ptr = (char *) "\n\\ No newline at end of file\n";
		mb[2].size = strlen(mb[2].ptr);
		i++;
	}
	if (ecb->outf(ecb->priv, mb, i) < 0) {

		return -1;
	}

	return 0;
}

void *xdl_mmfile_first(mmfile_t *mmf, long *size)
{
	*size = mmf->size;
	return mmf->ptr;
}


long xdl_mmfile_size(mmfile_t *mmf)
{
	return mmf->size;
}


int xdl_cha_init(chastore_t *cha, long isize, long icount) {

	cha->head = cha->tail = NULL;
	cha->isize = isize;
	cha->nsize = icount * isize;
	cha->ancur = cha->sncur = NULL;
	cha->scurr = 0;

	return 0;
}


void xdl_cha_free(chastore_t *cha) {
	chanode_t *cur, *tmp;

	for (cur = cha->head; (tmp = cur) != NULL;) {
		cur = cur->next;
		xdl_free(tmp);
	}
}


void *xdl_cha_alloc(chastore_t *cha) {
	chanode_t *ancur;
	void *data;

	if (!(ancur = cha->ancur) || ancur->icurr == cha->nsize) {
		if (!(ancur = (chanode_t *) xdl_malloc(sizeof(chanode_t) + cha->nsize))) {

			return NULL;
		}
		ancur->icurr = 0;
		ancur->next = NULL;
		if (cha->tail)
			cha->tail->next = ancur;
		if (!cha->head)
			cha->head = ancur;
		cha->tail = ancur;
		cha->ancur = ancur;
	}

	data = (char *) ancur + sizeof(chanode_t) + ancur->icurr;
	ancur->icurr += cha->isize;

	return data;
}

long xdl_guess_lines(mmfile_t *mf, long sample) {
	long nl = 0, size, tsize = 0;
	char const *data, *cur, *top;

	if ((cur = data = xdl_mmfile_first(mf, &size)) != NULL) {
		for (top = data + size; nl < sample && cur < top; ) {
			nl++;
			if (!(cur = memchr(cur, '\n', top - cur)))
				cur = top;
			else
				cur++;
		}
		tsize += (long) (cur - data);
	}

	if (nl && tsize)
		nl = xdl_mmfile_size(mf) / (tsize / nl);

	return nl + 1;
}

int xdl_blankline(const char *line, long size, long flags)
{
	long i;

	if (!(flags & XDF_WHITESPACE_FLAGS))
		return (size <= 1);

	for (i = 0; i < size && XDL_ISSPACE(line[i]); i++)
		;

	return (i == size);
}

/*
 * Have we eaten everything on the line, except for an optional
 * CR at the very end?
 */
static int ends_with_optional_cr(const char *l, long s, long i)
{
	int complete = s && l[s-1] == '\n';

	if (complete)
		s--;
	if (s == i)
		return 1;
	/* do not ignore CR at the end of an incomplete line */
	if (complete && s == i + 1 && l[i] == '\r')
		return 1;
	return 0;
}

int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags)
{
	int i1, i2;

	if (s1 == s2 && !memcmp(l1, l2, s1))
		return 1;
	if (!(flags & XDF_WHITESPACE_FLAGS))
		return 0;

	i1 = 0;
	i2 = 0;

	/*
	 * -w matches everything that matches with -b, and -b in turn
	 * matches everything that matches with --ignore-space-at-eol,
	 * which in turn matches everything that matches with --ignore-cr-at-eol.
	 *
	 * Each flavor of ignoring needs different logic to skip whitespaces
	 * while we have both sides to compare.
	 */
	if (flags & XDF_IGNORE_WHITESPACE) {
		goto skip_ws;
		while (i1 < s1 && i2 < s2) {
			if (l1[i1++] != l2[i2++])
				return 0;
		skip_ws:
			while (i1 < s1 && XDL_ISSPACE(l1[i1]))
				i1++;
			while (i2 < s2 && XDL_ISSPACE(l2[i2]))
				i2++;
		}
	} else if (flags & XDF_IGNORE_WHITESPACE_CHANGE) {
		while (i1 < s1 && i2 < s2) {
			if (XDL_ISSPACE(l1[i1]) && XDL_ISSPACE(l2[i2])) {
				/* Skip matching spaces and try again */
				while (i1 < s1 && XDL_ISSPACE(l1[i1]))
					i1++;
				while (i2 < s2 && XDL_ISSPACE(l2[i2]))
					i2++;
				continue;
			}
			if (l1[i1++] != l2[i2++])
				return 0;
		}
	} else if (flags & XDF_IGNORE_WHITESPACE_AT_EOL) {
		while (i1 < s1 && i2 < s2 && l1[i1] == l2[i2]) {
			i1++;
			i2++;
		}
	} else if (flags & XDF_IGNORE_CR_AT_EOL) {
		/* Find the first difference and see how the line ends */
		while (i1 < s1 && i2 < s2 && l1[i1] == l2[i2]) {
			i1++;
			i2++;
		}
		return (ends_with_optional_cr(l1, s1, i1) &&
			ends_with_optional_cr(l2, s2, i2));
	}

	/*
	 * After running out of one side, the remaining side must have
	 * nothing but whitespace for the lines to match.  Note that
	 * ignore-whitespace-at-eol case may break out of the loop
	 * while there still are characters remaining on both lines.
	 */
	if (i1 < s1) {
		while (i1 < s1 && XDL_ISSPACE(l1[i1]))
			i1++;
		if (s1 != i1)
			return 0;
	}
	if (i2 < s2) {
		while (i2 < s2 && XDL_ISSPACE(l2[i2]))
			i2++;
		return (s2 == i2);
	}
	return 1;
}

static unsigned long xdl_hash_record_with_whitespace(char const **data,
		char const *top, long flags) {
	unsigned long ha = 5381;
	char const *ptr = *data;
	int cr_at_eol_only = (flags & XDF_WHITESPACE_FLAGS) == XDF_IGNORE_CR_AT_EOL;

	for (; ptr < top && *ptr != '\n'; ptr++) {
		if (cr_at_eol_only) {
			/* do not ignore CR at the end of an incomplete line */
			if (*ptr == '\r' &&
			    (ptr + 1 < top && ptr[1] == '\n'))
				continue;
		}
		else if (XDL_ISSPACE(*ptr)) {
			const char *ptr2 = ptr;
			int at_eol;
			while (ptr + 1 < top && XDL_ISSPACE(ptr[1])
					&& ptr[1] != '\n')
				ptr++;
			at_eol = (top <= ptr + 1 || ptr[1] == '\n');
			if (flags & XDF_IGNORE_WHITESPACE)
				; /* already handled */
			else if (flags & XDF_IGNORE_WHITESPACE_CHANGE
				 && !at_eol) {
				ha += (ha << 5);
				ha ^= (unsigned long) ' ';
			}
			else if (flags & XDF_IGNORE_WHITESPACE_AT_EOL
				 && !at_eol) {
				while (ptr2 != ptr + 1) {
					ha += (ha << 5);
					ha ^= (unsigned long) *ptr2;
					ptr2++;
				}
			}
			continue;
		}
		ha += (ha << 5);
		ha ^= (unsigned long) *ptr;
	}
	*data = ptr < top ? ptr + 1: ptr;

	return ha;
}

unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
	unsigned long ha = 5381;
	char const *ptr = *data;

	if (flags & XDF_WHITESPACE_FLAGS)
		return xdl_hash_record_with_whitespace(data, top, flags);

	for (; ptr < top && *ptr != '\n'; ptr++) {
		ha += (ha << 5);
		ha ^= (unsigned long) *ptr;
	}
	*data = ptr < top ? ptr + 1: ptr;

	return ha;
}

unsigned int xdl_hashbits(unsigned int size) {
	unsigned int val = 1, bits = 0;

	for (; val < size && bits < CHAR_BIT * sizeof(unsigned int); val <<= 1, bits++);
	return bits ? bits: 1;
}


int xdl_num_out(char *out, long val) {
	char *ptr, *str = out;
	char buf[32];

	ptr = buf + sizeof(buf) - 1;
	*ptr = '\0';
	if (val < 0) {
		*--ptr = '-';
		val = -val;
	}
	for (; val && ptr > buf; val /= 10)
		*--ptr = "0123456789"[val % 10];
	if (*ptr)
		for (; *ptr; ptr++, str++)
			*str = *ptr;
	else
		*str++ = '0';
	*str = '\0';

	return str - out;
}

int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
		      const char *func, long funclen, xdemitcb_t *ecb) {
	int nb = 0;
	mmbuffer_t mb;
	char buf[128];

	memcpy(buf, "@@ -", 4);
	nb += 4;

	nb += xdl_num_out(buf + nb, c1 ? s1: s1 - 1);

	if (c1 != 1) {
		memcpy(buf + nb, ",", 1);
		nb += 1;

		nb += xdl_num_out(buf + nb, c1);
	}

	memcpy(buf + nb, " +", 2);
	nb += 2;

	nb += xdl_num_out(buf + nb, c2 ? s2: s2 - 1);

	if (c2 != 1) {
		memcpy(buf + nb, ",", 1);
		nb += 1;

		nb += xdl_num_out(buf + nb, c2);
	}

	memcpy(buf + nb, " @@", 3);
	nb += 3;
	if (func && funclen) {
		buf[nb++] = ' ';
		if (funclen > sizeof(buf) - nb - 1)
			funclen = sizeof(buf) - nb - 1;
		memcpy(buf + nb, func, funclen);
		nb += funclen;
	}
	buf[nb++] = '\n';

	mb.ptr = buf;
	mb.size = nb;
	if (ecb->outf(ecb->priv, &mb, 1) < 0)
		return -1;

	return 0;
}

int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
		int line1, int count1, int line2, int count2)
{
	/*
	 * This probably does not work outside Git, since
	 * we have a very simple mmfile structure.
	 *
	 * Note: ideally, we would reuse the prepared environment, but
	 * the libxdiff interface does not (yet) allow for diffing only
	 * ranges of lines instead of the whole files.
	 */
	mmfile_t subfile1, subfile2;
	xdfenv_t env;

	subfile1.ptr = (char *)diff_env->xdf1.recs[line1 - 1]->ptr;
	subfile1.size = diff_env->xdf1.recs[line1 + count1 - 2]->ptr +
		diff_env->xdf1.recs[line1 + count1 - 2]->size - subfile1.ptr;
	subfile2.ptr = (char *)diff_env->xdf2.recs[line2 - 1]->ptr;
	subfile2.size = diff_env->xdf2.recs[line2 + count2 - 2]->ptr +
		diff_env->xdf2.recs[line2 + count2 - 2]->size - subfile2.ptr;
	if (xdl_do_diff(&subfile1, &subfile2, xpp, &env) < 0)
		return -1;

	memcpy(diff_env->xdf1.rchg + line1 - 1, env.xdf1.rchg, count1);
	memcpy(diff_env->xdf2.rchg + line2 - 1, env.xdf2.rchg, count2);

	xdl_free_env(&env);

	return 0;
}