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65416758 JH |
1 | #include "cache.h" |
2 | #include "diff.h" | |
3 | #include "diffcore.h" | |
ba23bbc8 JH |
4 | |
5 | /* | |
6 | * Idea here is very simple. | |
7 | * | |
8 | * We have total of (sz-N+1) N-byte overlapping sequences in buf whose | |
9 | * size is sz. If the same N-byte sequence appears in both source and | |
10 | * destination, we say the byte that starts that sequence is shared | |
11 | * between them (i.e. copied from source to destination). | |
12 | * | |
13 | * For each possible N-byte sequence, if the source buffer has more | |
14 | * instances of it than the destination buffer, that means the | |
15 | * difference are the number of bytes not copied from source to | |
16 | * destination. If the counts are the same, everything was copied | |
17 | * from source to destination. If the destination has more, | |
18 | * everything was copied, and destination added more. | |
19 | * | |
20 | * We are doing an approximation so we do not really have to waste | |
21 | * memory by actually storing the sequence. We just hash them into | |
22 | * somewhere around 2^16 hashbuckets and count the occurrences. | |
23 | * | |
24 | * The length of the sequence is arbitrarily set to 8 for now. | |
25 | */ | |
26 | ||
c06c7966 | 27 | /* Wild guess at the initial hash size */ |
2821104d | 28 | #define INITIAL_HASH_SIZE 9 |
fc66d213 | 29 | |
2821104d JH |
30 | /* We leave more room in smaller hash but do not let it |
31 | * grow to have unused hole too much. | |
32 | */ | |
33 | #define INITIAL_FREE(sz_log2) ((1<<(sz_log2))*(sz_log2-3)/(sz_log2)) | |
ba23bbc8 | 34 | |
fc66d213 JH |
35 | /* A prime rather carefully chosen between 2^16..2^17, so that |
36 | * HASHBASE < INITIAL_FREE(17). We want to keep the maximum hashtable | |
37 | * size under the current 2<<17 maximum, which can hold this many | |
38 | * different values before overflowing to hashtable of size 2<<18. | |
39 | */ | |
40 | #define HASHBASE 107927 | |
41 | ||
c06c7966 | 42 | struct spanhash { |
e31c9f24 LT |
43 | unsigned int hashval; |
44 | unsigned int cnt; | |
c06c7966 JH |
45 | }; |
46 | struct spanhash_top { | |
47 | int alloc_log2; | |
48 | int free; | |
49 | struct spanhash data[FLEX_ARRAY]; | |
50 | }; | |
51 | ||
2821104d | 52 | static struct spanhash *spanhash_find(struct spanhash_top *top, |
e31c9f24 | 53 | unsigned int hashval) |
c06c7966 JH |
54 | { |
55 | int sz = 1 << top->alloc_log2; | |
56 | int bucket = hashval & (sz - 1); | |
57 | while (1) { | |
58 | struct spanhash *h = &(top->data[bucket++]); | |
59 | if (!h->cnt) | |
60 | return NULL; | |
61 | if (h->hashval == hashval) | |
62 | return h; | |
63 | if (sz <= bucket) | |
64 | bucket = 0; | |
65 | } | |
66 | } | |
67 | ||
68 | static struct spanhash_top *spanhash_rehash(struct spanhash_top *orig) | |
69 | { | |
70 | struct spanhash_top *new; | |
71 | int i; | |
72 | int osz = 1 << orig->alloc_log2; | |
73 | int sz = osz << 1; | |
74 | ||
75 | new = xmalloc(sizeof(*orig) + sizeof(struct spanhash) * sz); | |
76 | new->alloc_log2 = orig->alloc_log2 + 1; | |
2821104d | 77 | new->free = INITIAL_FREE(new->alloc_log2); |
c06c7966 JH |
78 | memset(new->data, 0, sizeof(struct spanhash) * sz); |
79 | for (i = 0; i < osz; i++) { | |
80 | struct spanhash *o = &(orig->data[i]); | |
81 | int bucket; | |
82 | if (!o->cnt) | |
83 | continue; | |
84 | bucket = o->hashval & (sz - 1); | |
85 | while (1) { | |
86 | struct spanhash *h = &(new->data[bucket++]); | |
87 | if (!h->cnt) { | |
88 | h->hashval = o->hashval; | |
89 | h->cnt = o->cnt; | |
90 | new->free--; | |
91 | break; | |
92 | } | |
93 | if (sz <= bucket) | |
94 | bucket = 0; | |
95 | } | |
96 | } | |
97 | free(orig); | |
98 | return new; | |
99 | } | |
100 | ||
101 | static struct spanhash_top *add_spanhash(struct spanhash_top *top, | |
e31c9f24 | 102 | unsigned int hashval, int cnt) |
c06c7966 JH |
103 | { |
104 | int bucket, lim; | |
105 | struct spanhash *h; | |
106 | ||
107 | lim = (1 << top->alloc_log2); | |
108 | bucket = hashval & (lim - 1); | |
109 | while (1) { | |
110 | h = &(top->data[bucket++]); | |
111 | if (!h->cnt) { | |
112 | h->hashval = hashval; | |
3c7ceba4 | 113 | h->cnt = cnt; |
c06c7966 JH |
114 | top->free--; |
115 | if (top->free < 0) | |
116 | return spanhash_rehash(top); | |
117 | return top; | |
118 | } | |
119 | if (h->hashval == hashval) { | |
3c7ceba4 | 120 | h->cnt += cnt; |
c06c7966 JH |
121 | return top; |
122 | } | |
123 | if (lim <= bucket) | |
124 | bucket = 0; | |
125 | } | |
126 | } | |
127 | ||
e31c9f24 | 128 | static struct spanhash_top *hash_chars(unsigned char *buf, unsigned int sz) |
65416758 | 129 | { |
3c7ceba4 | 130 | int i, n; |
e31c9f24 | 131 | unsigned int accum1, accum2, hashval; |
c06c7966 JH |
132 | struct spanhash_top *hash; |
133 | ||
134 | i = INITIAL_HASH_SIZE; | |
135 | hash = xmalloc(sizeof(*hash) + sizeof(struct spanhash) * (1<<i)); | |
136 | hash->alloc_log2 = i; | |
2821104d | 137 | hash->free = INITIAL_FREE(i); |
c06c7966 | 138 | memset(hash->data, 0, sizeof(struct spanhash) * (1<<i)); |
65416758 | 139 | |
3c7ceba4 LT |
140 | n = 0; |
141 | accum1 = accum2 = 0; | |
ba23bbc8 | 142 | while (sz) { |
e31c9f24 LT |
143 | unsigned int c = *buf++; |
144 | unsigned int old_1 = accum1; | |
ba23bbc8 | 145 | sz--; |
e31c9f24 LT |
146 | accum1 = (accum1 << 7) ^ (accum2 >> 25); |
147 | accum2 = (accum2 << 7) ^ (old_1 >> 25); | |
3c7ceba4 LT |
148 | accum1 += c; |
149 | if (++n < 64 && c != '\n') | |
150 | continue; | |
151 | hashval = (accum1 + accum2 * 0x61) % HASHBASE; | |
152 | hash = add_spanhash(hash, hashval, n); | |
153 | n = 0; | |
154 | accum1 = accum2 = 0; | |
65416758 | 155 | } |
c06c7966 | 156 | return hash; |
65416758 JH |
157 | } |
158 | ||
159 | int diffcore_count_changes(void *src, unsigned long src_size, | |
160 | void *dst, unsigned long dst_size, | |
c06c7966 JH |
161 | void **src_count_p, |
162 | void **dst_count_p, | |
65416758 JH |
163 | unsigned long delta_limit, |
164 | unsigned long *src_copied, | |
165 | unsigned long *literal_added) | |
166 | { | |
c06c7966 JH |
167 | int i, ssz; |
168 | struct spanhash_top *src_count, *dst_count; | |
ba23bbc8 JH |
169 | unsigned long sc, la; |
170 | ||
c06c7966 JH |
171 | src_count = dst_count = NULL; |
172 | if (src_count_p) | |
173 | src_count = *src_count_p; | |
174 | if (!src_count) { | |
175 | src_count = hash_chars(src, src_size); | |
176 | if (src_count_p) | |
177 | *src_count_p = src_count; | |
178 | } | |
179 | if (dst_count_p) | |
180 | dst_count = *dst_count_p; | |
181 | if (!dst_count) { | |
182 | dst_count = hash_chars(dst, dst_size); | |
183 | if (dst_count_p) | |
184 | *dst_count_p = dst_count; | |
185 | } | |
ba23bbc8 | 186 | sc = la = 0; |
c06c7966 JH |
187 | |
188 | ssz = 1 << src_count->alloc_log2; | |
189 | for (i = 0; i < ssz; i++) { | |
190 | struct spanhash *s = &(src_count->data[i]); | |
191 | struct spanhash *d; | |
192 | unsigned dst_cnt, src_cnt; | |
193 | if (!s->cnt) | |
194 | continue; | |
195 | src_cnt = s->cnt; | |
196 | d = spanhash_find(dst_count, s->hashval); | |
197 | dst_cnt = d ? d->cnt : 0; | |
198 | if (src_cnt < dst_cnt) { | |
199 | la += dst_cnt - src_cnt; | |
200 | sc += src_cnt; | |
ba23bbc8 | 201 | } |
c06c7966 JH |
202 | else |
203 | sc += dst_cnt; | |
ba23bbc8 | 204 | } |
c06c7966 JH |
205 | |
206 | if (!src_count_p) | |
207 | free(src_count); | |
208 | if (!dst_count_p) | |
209 | free(dst_count); | |
ba23bbc8 JH |
210 | *src_copied = sc; |
211 | *literal_added = la; | |
ba23bbc8 | 212 | return 0; |
65416758 | 213 | } |