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1 | #include "cache.h" | |
2 | #include "diff.h" | |
3 | #include "diffcore.h" | |
4 | ||
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 | */ | |
23 | ||
24 | /* Wild guess at the initial hash size */ | |
25 | #define INITIAL_HASH_SIZE 9 | |
26 | ||
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)) | |
31 | ||
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 | |
38 | ||
39 | struct spanhash { | |
40 | unsigned int hashval; | |
41 | unsigned int cnt; | |
42 | }; | |
43 | struct spanhash_top { | |
44 | int alloc_log2; | |
45 | int free; | |
46 | struct spanhash data[FLEX_ARRAY]; | |
47 | }; | |
48 | ||
49 | static struct spanhash_top *spanhash_rehash(struct spanhash_top *orig) | |
50 | { | |
51 | struct spanhash_top *new; | |
52 | int i; | |
53 | int osz = 1 << orig->alloc_log2; | |
54 | int sz = osz << 1; | |
55 | ||
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; | |
80 | } | |
81 | ||
82 | static struct spanhash_top *add_spanhash(struct spanhash_top *top, | |
83 | unsigned int hashval, int cnt) | |
84 | { | |
85 | int bucket, lim; | |
86 | struct spanhash *h; | |
87 | ||
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 | } | |
107 | } | |
108 | ||
109 | static int spanhash_cmp(const void *a_, const void *b_) | |
110 | { | |
111 | const struct spanhash *a = a_; | |
112 | const struct spanhash *b = b_; | |
113 | ||
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; | |
121 | } | |
122 | ||
123 | static struct spanhash_top *hash_chars(struct diff_filespec *one) | |
124 | { | |
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); | |
131 | ||
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)); | |
137 | ||
138 | n = 0; | |
139 | accum1 = accum2 = 0; | |
140 | while (sz) { | |
141 | unsigned int c = *buf++; | |
142 | unsigned int old_1 = accum1; | |
143 | sz--; | |
144 | ||
145 | /* Ignore CR in CRLF sequence if text */ | |
146 | if (is_text && c == '\r' && sz && *buf == '\n') | |
147 | continue; | |
148 | ||
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; | |
164 | } | |
165 | ||
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) | |
173 | { | |
174 | struct spanhash *s, *d; | |
175 | struct spanhash_top *src_count, *dst_count; | |
176 | unsigned long sc, la; | |
177 | ||
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; | |
194 | ||
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 | } | |
225 | ||
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; | |
233 | } |