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comparison mercurial/bdiff.c @ 400:8b067bde6679

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Add a fast binary diff extension (not yet used) -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Add a fast binary diff extension (not yet used) manifest hash: fbfdcab2b1f4856af45176fcf2423d602dfe88c4 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.0 (GNU/Linux) iD8DBQFCuL6eywK+sNU5EO8RAoT+AJ95z9gx2IrucBS30CnCQFkZT7lSbgCgnXh5 ScZcgwzJ/mEo9i5vuKNlCIs= =Gr58 -----END PGP SIGNATURE-----
author mpm@selenic.com
date Tue, 21 Jun 2005 17:27:58 -0800
parents
children 9e9f7ab43ce2
comparison
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399:f060d728fe54 400:8b067bde6679
1 /*
2 bdiff.c - efficient binary diff extension for Mercurial
3
4 Copyright 2005 Matt Mackall <mpm@selenic.com>
5
6 This software may be used and distributed according to the terms of
7 the GNU General Public License, incorporated herein by reference.
8
9 Based roughly on Python difflib
10 */
11
12 #include <Python.h>
13 #include <stdlib.h>
14 #include <string.h>
15 #include <netinet/in.h>
16 #include <sys/types.h>
17
18 struct line {
19 int h, len, n;
20 const char *l;
21 };
22
23 struct hunk {
24 int a1, a2, b1, b2;
25 };
26
27 struct hunklist {
28 struct hunk *base, *head;
29 };
30
31 static inline uint32_t rol32(uint32_t word, unsigned int shift)
32 {
33 return (word << shift) | (word >> (32 - shift));
34 }
35
36 int splitlines(const char *a, int len, struct line **lr)
37 {
38 int h, i;
39 const char *p, *b = a;
40 struct line *l;
41
42 /* count the lines */
43 i = 1; /* extra line for sentinel */
44 for (p = a; p < a + len; p++)
45 if (*p == '\n' || p == a + len - 1)
46 i++;
47
48 *lr = l = malloc(sizeof(struct line) * i);
49 if (!l)
50 return -1;
51
52 /* build the line array and calculate hashes */
53 h = 0;
54 for (p = a; p < a + len; p++) {
55 h = *p + rol32(h, 7); /* a simple hash from GNU diff */
56 if (*p == '\n' || p == a + len - 1) {
57 l->len = p - b + 1;
58 l->h = h;
59 l->l = b;
60 l->n = -1;
61 l++;
62 b = p + 1;
63 h = 0;
64 }
65 }
66
67 /* set up a sentinel */
68 l->h = l->len = 0;
69 l->l = a + len;
70 return i - 1;
71 }
72
73 int inline cmp(struct line *a, struct line *b)
74 {
75 return a->len != b->len || memcmp(a->l, b->l, a->len);
76 }
77
78 static int equatelines(struct line *a, int an, struct line *b, int bn)
79 {
80 int i, j, buckets = 1, t, *h, *l;
81
82 /* build a hash table of the next highest power of 2 */
83 while (buckets < bn + 1)
84 buckets *= 2;
85
86 h = malloc(buckets * sizeof(int));
87 l = calloc(buckets, sizeof(int));
88 buckets = buckets - 1;
89 if (!h || !l) {
90 free(h);
91 return 0;
92 }
93
94 /* clear the hash table */
95 for (i = 0; i <= buckets; i++)
96 h[i] = -1;
97
98 /* add lines to the hash table chains */
99 for (i = bn - 1; i >= 0; i--) {
100 /* find the equivalence class */
101 for (j = b[i].h & buckets; h[j] != -1; j = (j + 1) & buckets)
102 if (!cmp(b + i, b + h[j]))
103 break;
104
105 /* add to the head of the equivalence class */
106 b[i].n = h[j];
107 b[i].h = j;
108 h[j] = i;
109 l[j]++; /* keep track of popularity */
110 }
111
112 /* compute popularity threshold */
113 t = (bn >= 200) ? bn / 100 : bn + 1;
114
115 /* match items in a to their equivalence class in b */
116 for (i = 0; i < an; i++) {
117 /* find the equivalence class */
118 for (j = a[i].h & buckets; h[j] != -1; j = (j + 1) & buckets)
119 if (!cmp(a + i, b + h[j]))
120 break;
121
122 a[i].h = j; /* use equivalence class for quick compare */
123 if(l[j] <= t)
124 a[i].n = h[j]; /* point to head of match list */
125 else
126 a[i].n = -1; /* too popular */
127 }
128
129 /* discard hash tables */
130 free(h);
131 free(l);
132 return 1;
133 }
134
135 static int longest_match(struct line *a, struct line *b, int *jpos, int *jlen,
136 int a1, int a2, int b1, int b2, int *omi, int *omj)
137 {
138 int mi = a1, mj = b1, mk = 0, mb = 0, i, j, k;
139
140 for (i = a1; i < a2; i++) {
141 /* skip things before the current block */
142 for (j = a[i].n; j != -1 && j < b1; j = b[j].n)
143 ;
144
145 /* loop through all lines match a[i] in b */
146 for (; j != -1 && j < b2; j = b[j].n) {
147 /* does this extend an earlier match? */
148 if (i > a1 && j > b1 && jpos[j - 1] == i)
149 k = jlen[j - 1] + 1;
150 else
151 k = 1;
152 jpos[j] = i + 1;
153 jlen[j] = k;
154
155 /* best match so far? */
156 if (k > mk) {
157 mi = i;
158 mj = j;
159 mk = k;
160 }
161 }
162 }
163
164 if (mk) {
165 mi = mi - mk + 1;
166 mj = mj - mk + 1;
167 }
168
169 /* expand match to include neighboring popular lines */
170 while (mi - mb > a1 && mj - mb > b1 &&
171 a[mi - mb - 1].h == b[mj - mb - 1].h)
172 mb++;
173 while (mi + mk < a2 && mj + mk < b2 &&
174 a[mi + mk].h == b[mj + mk].h)
175 mk++;
176
177 *omi = mi - mb;
178 *omj = mj - mb;
179 return mk + mb;
180 }
181
182 static void recurse(struct line *a, struct line *b, int *jpos, int *jlen,
183 int a1, int a2, int b1, int b2, struct hunklist *l)
184 {
185 int i, j, k;
186
187 /* find the longest match in this chunk */
188 k = longest_match(a, b, jpos, jlen, a1, a2, b1, b2, &i, &j);
189 if (!k)
190 return;
191
192 /* and recurse on the remaining chunks on either side */
193 recurse(a, b, jpos, jlen, a1, i, b1, j, l);
194 l->head->a1 = i;
195 l->head->a2 = i + k;
196 l->head->b1 = j;
197 l->head->b2 = j + k;
198 l->head++;
199 recurse(a, b, jpos, jlen, i + k, a2, j + k, b2, l);
200 }
201
202 static PyObject *bdiff(PyObject *self, PyObject *args)
203 {
204 PyObject *sa, *sb, *result = NULL;
205 struct hunklist l;
206 struct hunk *h;
207 struct line *al, *bl;
208 char encode[12], *rb;
209 int an, bn, len = 0, t, la = 0, lb = 0, *jpos, *jlen;
210
211 if (!PyArg_ParseTuple(args, "SS:bdiff", &sa, &sb))
212 return NULL;
213
214 /* allocate and fill arrays */
215 an = splitlines(PyString_AsString(sa), PyString_Size(sa), &al);
216 bn = splitlines(PyString_AsString(sb), PyString_Size(sb), &bl);
217 t = equatelines(al, an, bl, bn);
218 jpos = calloc(bn, sizeof(int));
219 jlen = calloc(bn, sizeof(int));
220 l.head = l.base = malloc(sizeof(struct hunk) * ((an + bn) / 4 + 2));
221 if (!al || !bl || !jpos || !jlen || !l.base || !t)
222 goto nomem;
223
224 /* generate the matching block list */
225 recurse(al, bl, jpos, jlen, 0, an, 0, bn, &l);
226 l.head->a1 = an;
227 l.head->b1 = bn;
228 l.head++;
229
230 /* calculate length of output */
231 for(h = l.base; h != l.head; h++) {
232 if (h->a1 != la || h->b1 != lb)
233 len += 12 + bl[h->b1].l - bl[lb].l;
234 la = h->a2;
235 lb = h->b2;
236 }
237
238 result = PyString_FromStringAndSize(NULL, len);
239 if (!result)
240 goto nomem;
241
242 /* build binary patch */
243 rb = PyString_AsString(result);
244 la = lb = 0;
245
246 for(h = l.base; h != l.head; h++) {
247 if (h->a1 != la || h->b1 != lb) {
248 len = bl[h->b1].l - bl[lb].l;
249 *(uint32_t *)(encode) = htonl(al[la].l - al->l);
250 *(uint32_t *)(encode + 4) = htonl(al[h->a1].l - al->l);
251 *(uint32_t *)(encode + 8) = htonl(len);
252 memcpy(rb, encode, 12);
253 memcpy(rb + 12, bl[lb].l, len);
254 rb += 12 + len;
255 }
256 la = h->a2;
257 lb = h->b2;
258 }
259
260 nomem:
261 free(al);
262 free(bl);
263 free(jpos);
264 free(jlen);
265 free(l.base);
266 return result ? result : PyErr_NoMemory();
267 }
268
269 static char mdiff_doc[] = "Efficient binary diff.";
270
271 static PyMethodDef methods[] = {
272 {"bdiff", bdiff, METH_VARARGS, "calculate a binary diff\n"},
273 {NULL, NULL}
274 };
275
276 PyMODINIT_FUNC initbdiff(void)
277 {
278 Py_InitModule3("bdiff", methods, mdiff_doc);
279 }