mercurial/cext/bdiff.c

revlog: add a "data compression mode" entry in the index tuple

That will make it possible to keep track of compression information in the
revlog index, opening the way to more efficient revision restoration (in native
code, but the python usage is already defeating performance work).

We start with adding a new entry to the index tuple, using a value matching the
current behavior. We will introduce storage and other value in later changesets.

Differential Revision: https://phab.mercurial-scm.org/D10646

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

 Copyright 2005, 2006 Olivia 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 <limits.h>
#include <stdlib.h>
#include <string.h>

#include "bdiff.h"
#include "bitmanipulation.h"
#include "thirdparty/xdiff/xdiff.h"
#include "util.h"

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

	l.next = NULL;

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

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

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

	count = bdiff_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);
	bdiff_freehunks(l.next);
	return rl ? rl : PyErr_NoMemory();
}

static PyObject *bdiff(PyObject *self, PyObject *args)
{
	Py_buffer ba, bb;
	char *rb, *ia, *ib;
	PyObject *result = NULL;
	struct bdiff_line *al = NULL, *bl = NULL;
	struct bdiff_hunk l, *h;
	int an, bn, count;
	Py_ssize_t len = 0, la, lb, li = 0, lcommon = 0, lmax;
	PyThreadState *_save = NULL;

	l.next = NULL;

	if (!PyArg_ParseTuple(args, PY23("s*s*:bdiff", "y*y*:bdiff"), &ba,
	                      &bb)) {
		return NULL;
	}

	if (!PyBuffer_IsContiguous(&ba, 'C') || ba.ndim > 1) {
		PyErr_SetString(PyExc_ValueError, "bdiff input not contiguous");
		goto cleanup;
	}

	if (!PyBuffer_IsContiguous(&bb, 'C') || bb.ndim > 1) {
		PyErr_SetString(PyExc_ValueError, "bdiff input not contiguous");
		goto cleanup;
	}

	la = ba.len;
	lb = bb.len;

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

	_save = PyEval_SaveThread();

	lmax = la > lb ? lb : la;
	for (ia = ba.buf, ib = bb.buf; li < lmax && *ia == *ib;
	     ++li, ++ia, ++ib) {
		if (*ia == '\n') {
			lcommon = li + 1;
		}
	}
	/* we can almost add: if (li == lmax) lcommon = li; */

	an = bdiff_splitlines((char *)ba.buf + lcommon, la - lcommon, &al);
	bn = bdiff_splitlines((char *)bb.buf + lcommon, lb - lcommon, &bl);
	if (!al || !bl) {
		PyErr_NoMemory();
		goto cleanup;
	}

	count = bdiff_diff(al, an, bl, bn, &l);
	if (count < 0) {
		PyErr_NoMemory();
		goto cleanup;
	}

	/* 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 cleanup;
	}

	/* 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 + lcommon - al->l), rb);
			putbe32((uint32_t)(al[h->a1].l + lcommon - 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;
	}

cleanup:
	if (_save) {
		PyEval_RestoreThread(_save);
	}
	PyBuffer_Release(&ba);
	PyBuffer_Release(&bb);
	free(al);
	free(bl);
	bdiff_freehunks(l.next);
	return result;
}

/*
 * 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 *)PyMem_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:
	PyMem_Free(w);
	return result ? result : PyErr_NoMemory();
}

static bool sliceintolist(PyObject *list, Py_ssize_t destidx,
                          const char *source, Py_ssize_t len)
{
	PyObject *sliced = PyBytes_FromStringAndSize(source, len);
	if (sliced == NULL) {
		return false;
	}
	PyList_SET_ITEM(list, destidx, sliced);
	return true;
}

static PyObject *splitnewlines(PyObject *self, PyObject *args)
{
	const char *text;
	Py_ssize_t nelts = 0, size, i, start = 0;
	PyObject *result = NULL;

	if (!PyArg_ParseTuple(args, PY23("s#", "y#"), &text, &size)) {
		goto abort;
	}
	if (!size) {
		return PyList_New(0);
	}
	/* This loops to size-1 because if the last byte is a newline,
	 * we don't want to perform a split there. */
	for (i = 0; i < size - 1; ++i) {
		if (text[i] == '\n') {
			++nelts;
		}
	}
	if ((result = PyList_New(nelts + 1)) == NULL) {
		goto abort;
	}
	nelts = 0;
	for (i = 0; i < size - 1; ++i) {
		if (text[i] == '\n') {
			if (!sliceintolist(result, nelts++, text + start,
			                   i - start + 1)) {
				goto abort;
			}
			start = i + 1;
		}
	}
	if (!sliceintolist(result, nelts++, text + start, size - start)) {
		goto abort;
	}
	return result;
abort:
	Py_XDECREF(result);
	return NULL;
}

static int hunk_consumer(int64_t a1, int64_t a2, int64_t b1, int64_t b2,
                         void *priv)
{
	PyObject *rl = (PyObject *)priv;
	PyObject *m = Py_BuildValue("LLLL", a1, a2, b1, b2);
	int r;
	if (!m) {
		return -1;
	}
	r = PyList_Append(rl, m);
	Py_DECREF(m);
	return r;
}

static PyObject *xdiffblocks(PyObject *self, PyObject *args)
{
	Py_ssize_t la, lb;
	mmfile_t a, b;
	PyObject *rl;

	xpparam_t xpp = {
	    XDF_INDENT_HEURISTIC, /* flags */
	};
	xdemitconf_t xecfg = {
	    XDL_EMIT_BDIFFHUNK, /* flags */
	    hunk_consumer,      /* hunk_consume_func */
	};
	xdemitcb_t ecb = {
	    NULL, /* priv */
	};

	if (!PyArg_ParseTuple(args, PY23("s#s#", "y#y#"), &a.ptr, &la, &b.ptr,
	                      &lb)) {
		return NULL;
	}

	a.size = la;
	b.size = lb;

	rl = PyList_New(0);
	if (!rl) {
		return PyErr_NoMemory();
	}

	ecb.priv = rl;

	if (xdl_diff(&a, &b, &xpp, &xecfg, &ecb) != 0) {
		Py_DECREF(rl);
		return PyErr_NoMemory();
	}

	return rl;
}

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"},
    {"splitnewlines", splitnewlines, METH_VARARGS,
     "like str.splitlines, but only split on newlines\n"},
    {"xdiffblocks", xdiffblocks, METH_VARARGS,
     "find a list of matching lines using xdiff algorithm\n"},
    {NULL, NULL},
};

static const int version = 3;

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

PyMODINIT_FUNC PyInit_bdiff(void)
{
	PyObject *m;
	m = PyModule_Create(&bdiff_module);
	PyModule_AddIntConstant(m, "version", version);
	return m;
}
#else
PyMODINIT_FUNC initbdiff(void)
{
	PyObject *m;
	m = Py_InitModule3("bdiff", methods, mdiff_doc);
	PyModule_AddIntConstant(m, "version", version);
}
#endif