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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 |
ba23bbc8 | 29 | #define HASHBASE 65537 /* next_prime(2^16) */ |
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 | |
c06c7966 JH |
35 | struct spanhash { |
36 | unsigned long hashval; | |
37 | unsigned long cnt; | |
38 | }; | |
39 | struct spanhash_top { | |
40 | int alloc_log2; | |
41 | int free; | |
42 | struct spanhash data[FLEX_ARRAY]; | |
43 | }; | |
44 | ||
2821104d JH |
45 | static struct spanhash *spanhash_find(struct spanhash_top *top, |
46 | unsigned long hashval) | |
c06c7966 JH |
47 | { |
48 | int sz = 1 << top->alloc_log2; | |
49 | int bucket = hashval & (sz - 1); | |
50 | while (1) { | |
51 | struct spanhash *h = &(top->data[bucket++]); | |
52 | if (!h->cnt) | |
53 | return NULL; | |
54 | if (h->hashval == hashval) | |
55 | return h; | |
56 | if (sz <= bucket) | |
57 | bucket = 0; | |
58 | } | |
59 | } | |
60 | ||
61 | static struct spanhash_top *spanhash_rehash(struct spanhash_top *orig) | |
62 | { | |
63 | struct spanhash_top *new; | |
64 | int i; | |
65 | int osz = 1 << orig->alloc_log2; | |
66 | int sz = osz << 1; | |
67 | ||
68 | new = xmalloc(sizeof(*orig) + sizeof(struct spanhash) * sz); | |
69 | new->alloc_log2 = orig->alloc_log2 + 1; | |
2821104d | 70 | new->free = INITIAL_FREE(new->alloc_log2); |
c06c7966 JH |
71 | memset(new->data, 0, sizeof(struct spanhash) * sz); |
72 | for (i = 0; i < osz; i++) { | |
73 | struct spanhash *o = &(orig->data[i]); | |
74 | int bucket; | |
75 | if (!o->cnt) | |
76 | continue; | |
77 | bucket = o->hashval & (sz - 1); | |
78 | while (1) { | |
79 | struct spanhash *h = &(new->data[bucket++]); | |
80 | if (!h->cnt) { | |
81 | h->hashval = o->hashval; | |
82 | h->cnt = o->cnt; | |
83 | new->free--; | |
84 | break; | |
85 | } | |
86 | if (sz <= bucket) | |
87 | bucket = 0; | |
88 | } | |
89 | } | |
90 | free(orig); | |
91 | return new; | |
92 | } | |
93 | ||
94 | static struct spanhash_top *add_spanhash(struct spanhash_top *top, | |
95 | unsigned long hashval) | |
96 | { | |
97 | int bucket, lim; | |
98 | struct spanhash *h; | |
99 | ||
100 | lim = (1 << top->alloc_log2); | |
101 | bucket = hashval & (lim - 1); | |
102 | while (1) { | |
103 | h = &(top->data[bucket++]); | |
104 | if (!h->cnt) { | |
105 | h->hashval = hashval; | |
106 | h->cnt = 1; | |
107 | top->free--; | |
108 | if (top->free < 0) | |
109 | return spanhash_rehash(top); | |
110 | return top; | |
111 | } | |
112 | if (h->hashval == hashval) { | |
113 | h->cnt++; | |
114 | return top; | |
115 | } | |
116 | if (lim <= bucket) | |
117 | bucket = 0; | |
118 | } | |
119 | } | |
120 | ||
121 | static struct spanhash_top *hash_chars(unsigned char *buf, unsigned long sz) | |
65416758 | 122 | { |
c06c7966 JH |
123 | int i; |
124 | unsigned long accum1, accum2, hashval; | |
125 | struct spanhash_top *hash; | |
126 | ||
127 | i = INITIAL_HASH_SIZE; | |
128 | hash = xmalloc(sizeof(*hash) + sizeof(struct spanhash) * (1<<i)); | |
129 | hash->alloc_log2 = i; | |
2821104d | 130 | hash->free = INITIAL_FREE(i); |
c06c7966 | 131 | memset(hash->data, 0, sizeof(struct spanhash) * (1<<i)); |
65416758 | 132 | |
ba23bbc8 JH |
133 | /* an 8-byte shift register made of accum1 and accum2. New |
134 | * bytes come at LSB of accum2, and shifted up to accum1 | |
135 | */ | |
136 | for (i = accum1 = accum2 = 0; i < 7; i++, sz--) { | |
137 | accum1 = (accum1 << 8) | (accum2 >> 24); | |
138 | accum2 = (accum2 << 8) | *buf++; | |
139 | } | |
140 | while (sz) { | |
141 | accum1 = (accum1 << 8) | (accum2 >> 24); | |
142 | accum2 = (accum2 << 8) | *buf++; | |
c06c7966 JH |
143 | hashval = (accum1 + accum2 * 0x61) % HASHBASE; |
144 | hash = add_spanhash(hash, hashval); | |
ba23bbc8 | 145 | sz--; |
65416758 | 146 | } |
c06c7966 | 147 | return hash; |
65416758 JH |
148 | } |
149 | ||
150 | int diffcore_count_changes(void *src, unsigned long src_size, | |
151 | void *dst, unsigned long dst_size, | |
c06c7966 JH |
152 | void **src_count_p, |
153 | void **dst_count_p, | |
65416758 JH |
154 | unsigned long delta_limit, |
155 | unsigned long *src_copied, | |
156 | unsigned long *literal_added) | |
157 | { | |
c06c7966 JH |
158 | int i, ssz; |
159 | struct spanhash_top *src_count, *dst_count; | |
ba23bbc8 JH |
160 | unsigned long sc, la; |
161 | ||
162 | if (src_size < 8 || dst_size < 8) | |
163 | return -1; | |
164 | ||
c06c7966 JH |
165 | src_count = dst_count = NULL; |
166 | if (src_count_p) | |
167 | src_count = *src_count_p; | |
168 | if (!src_count) { | |
169 | src_count = hash_chars(src, src_size); | |
170 | if (src_count_p) | |
171 | *src_count_p = src_count; | |
172 | } | |
173 | if (dst_count_p) | |
174 | dst_count = *dst_count_p; | |
175 | if (!dst_count) { | |
176 | dst_count = hash_chars(dst, dst_size); | |
177 | if (dst_count_p) | |
178 | *dst_count_p = dst_count; | |
179 | } | |
ba23bbc8 | 180 | sc = la = 0; |
c06c7966 JH |
181 | |
182 | ssz = 1 << src_count->alloc_log2; | |
183 | for (i = 0; i < ssz; i++) { | |
184 | struct spanhash *s = &(src_count->data[i]); | |
185 | struct spanhash *d; | |
186 | unsigned dst_cnt, src_cnt; | |
187 | if (!s->cnt) | |
188 | continue; | |
189 | src_cnt = s->cnt; | |
190 | d = spanhash_find(dst_count, s->hashval); | |
191 | dst_cnt = d ? d->cnt : 0; | |
192 | if (src_cnt < dst_cnt) { | |
193 | la += dst_cnt - src_cnt; | |
194 | sc += src_cnt; | |
ba23bbc8 | 195 | } |
c06c7966 JH |
196 | else |
197 | sc += dst_cnt; | |
ba23bbc8 | 198 | } |
c06c7966 JH |
199 | |
200 | if (!src_count_p) | |
201 | free(src_count); | |
202 | if (!dst_count_p) | |
203 | free(dst_count); | |
ba23bbc8 JH |
204 | *src_copied = sc; |
205 | *literal_added = la; | |
ba23bbc8 | 206 | return 0; |
65416758 | 207 | } |