French translation: copy -> copie.
[git/dscho.git] / diffcore-delta.c
blob7cf431d261f9a35679ead7c8acda15aecdb8720d
1 #include "cache.h"
2 #include "diff.h"
3 #include "diffcore.h"
5 /*
6  * Idea here is very simple.
7  *
8  * Almost all data we are interested in are text, but sometimes we have
9  * to deal with binary data.  So we cut them into chunks delimited by
10  * LF byte, or 64-byte sequence, whichever comes first, and hash them.
11  *
12  * For those chunks, if the source buffer has more instances of it
13  * than the destination buffer, that means the difference are the
14  * number of bytes not copied from source to destination.  If the
15  * counts are the same, everything was copied from source to
16  * destination.  If the destination has more, everything was copied,
17  * and destination added more.
18  *
19  * We are doing an approximation so we do not really have to waste
20  * memory by actually storing the sequence.  We just hash them into
21  * somewhere around 2^16 hashbuckets and count the occurrences.
22  */
24 /* Wild guess at the initial hash size */
25 #define INITIAL_HASH_SIZE 9
27 /* We leave more room in smaller hash but do not let it
28  * grow to have unused hole too much.
29  */
30 #define INITIAL_FREE(sz_log2) ((1<<(sz_log2))*(sz_log2-3)/(sz_log2))
32 /* A prime rather carefully chosen between 2^16..2^17, so that
33  * HASHBASE < INITIAL_FREE(17).  We want to keep the maximum hashtable
34  * size under the current 2<<17 maximum, which can hold this many
35  * different values before overflowing to hashtable of size 2<<18.
36  */
37 #define HASHBASE 107927
39 struct spanhash {
40         unsigned int hashval;
41         unsigned int cnt;
43 struct spanhash_top {
44         int alloc_log2;
45         int free;
46         struct spanhash data[FLEX_ARRAY];
49 static struct spanhash_top *spanhash_rehash(struct spanhash_top *orig)
51         struct spanhash_top *new;
52         int i;
53         int osz = 1 << orig->alloc_log2;
54         int sz = osz << 1;
56         new = xmalloc(sizeof(*orig) + sizeof(struct spanhash) * sz);
57         new->alloc_log2 = orig->alloc_log2 + 1;
58         new->free = INITIAL_FREE(new->alloc_log2);
59         memset(new->data, 0, sizeof(struct spanhash) * sz);
60         for (i = 0; i < osz; i++) {
61                 struct spanhash *o = &(orig->data[i]);
62                 int bucket;
63                 if (!o->cnt)
64                         continue;
65                 bucket = o->hashval & (sz - 1);
66                 while (1) {
67                         struct spanhash *h = &(new->data[bucket++]);
68                         if (!h->cnt) {
69                                 h->hashval = o->hashval;
70                                 h->cnt = o->cnt;
71                                 new->free--;
72                                 break;
73                         }
74                         if (sz <= bucket)
75                                 bucket = 0;
76                 }
77         }
78         free(orig);
79         return new;
82 static struct spanhash_top *add_spanhash(struct spanhash_top *top,
83                                          unsigned int hashval, int cnt)
85         int bucket, lim;
86         struct spanhash *h;
88         lim = (1 << top->alloc_log2);
89         bucket = hashval & (lim - 1);
90         while (1) {
91                 h = &(top->data[bucket++]);
92                 if (!h->cnt) {
93                         h->hashval = hashval;
94                         h->cnt = cnt;
95                         top->free--;
96                         if (top->free < 0)
97                                 return spanhash_rehash(top);
98                         return top;
99                 }
100                 if (h->hashval == hashval) {
101                         h->cnt += cnt;
102                         return top;
103                 }
104                 if (lim <= bucket)
105                         bucket = 0;
106         }
109 static int spanhash_cmp(const void *a_, const void *b_)
111         const struct spanhash *a = a_;
112         const struct spanhash *b = b_;
114         /* A count of zero compares at the end.. */
115         if (!a->cnt)
116                 return !b->cnt ? 0 : 1;
117         if (!b->cnt)
118                 return -1;
119         return a->hashval < b->hashval ? -1 :
120                 a->hashval > b->hashval ? 1 : 0;
123 static struct spanhash_top *hash_chars(struct diff_filespec *one)
125         int i, n;
126         unsigned int accum1, accum2, hashval;
127         struct spanhash_top *hash;
128         unsigned char *buf = one->data;
129         unsigned int sz = one->size;
130         int is_text = !diff_filespec_is_binary(one);
132         i = INITIAL_HASH_SIZE;
133         hash = xmalloc(sizeof(*hash) + sizeof(struct spanhash) * (1<<i));
134         hash->alloc_log2 = i;
135         hash->free = INITIAL_FREE(i);
136         memset(hash->data, 0, sizeof(struct spanhash) * (1<<i));
138         n = 0;
139         accum1 = accum2 = 0;
140         while (sz) {
141                 unsigned int c = *buf++;
142                 unsigned int old_1 = accum1;
143                 sz--;
145                 /* Ignore CR in CRLF sequence if text */
146                 if (is_text && c == '\r' && sz && *buf == '\n')
147                         continue;
149                 accum1 = (accum1 << 7) ^ (accum2 >> 25);
150                 accum2 = (accum2 << 7) ^ (old_1 >> 25);
151                 accum1 += c;
152                 if (++n < 64 && c != '\n')
153                         continue;
154                 hashval = (accum1 + accum2 * 0x61) % HASHBASE;
155                 hash = add_spanhash(hash, hashval, n);
156                 n = 0;
157                 accum1 = accum2 = 0;
158         }
159         qsort(hash->data,
160                 1ul << hash->alloc_log2,
161                 sizeof(hash->data[0]),
162                 spanhash_cmp);
163         return hash;
166 int diffcore_count_changes(struct diff_filespec *src,
167                            struct diff_filespec *dst,
168                            void **src_count_p,
169                            void **dst_count_p,
170                            unsigned long delta_limit,
171                            unsigned long *src_copied,
172                            unsigned long *literal_added)
174         struct spanhash *s, *d;
175         struct spanhash_top *src_count, *dst_count;
176         unsigned long sc, la;
178         src_count = dst_count = NULL;
179         if (src_count_p)
180                 src_count = *src_count_p;
181         if (!src_count) {
182                 src_count = hash_chars(src);
183                 if (src_count_p)
184                         *src_count_p = src_count;
185         }
186         if (dst_count_p)
187                 dst_count = *dst_count_p;
188         if (!dst_count) {
189                 dst_count = hash_chars(dst);
190                 if (dst_count_p)
191                         *dst_count_p = dst_count;
192         }
193         sc = la = 0;
195         s = src_count->data;
196         d = dst_count->data;
197         for (;;) {
198                 unsigned dst_cnt, src_cnt;
199                 if (!s->cnt)
200                         break; /* we checked all in src */
201                 while (d->cnt) {
202                         if (d->hashval >= s->hashval)
203                                 break;
204                         la += d->cnt;
205                         d++;
206                 }
207                 src_cnt = s->cnt;
208                 dst_cnt = 0;
209                 if (d->cnt && d->hashval == s->hashval) {
210                         dst_cnt = d->cnt;
211                         d++;
212                 }
213                 if (src_cnt < dst_cnt) {
214                         la += dst_cnt - src_cnt;
215                         sc += src_cnt;
216                 }
217                 else
218                         sc += dst_cnt;
219                 s++;
220         }
221         while (d->cnt) {
222                 la += d->cnt;
223                 d++;
224         }
226         if (!src_count_p)
227                 free(src_count);
228         if (!dst_count_p)
229                 free(dst_count);
230         *src_copied = sc;
231         *literal_added = la;
232         return 0;