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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 | * | |
af3abef9 JH |
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. | |
ba23bbc8 | 11 | * |
af3abef9 JH |
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. | |
ba23bbc8 JH |
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. | |
ba23bbc8 JH |
22 | */ |
23 | ||
c06c7966 | 24 | /* Wild guess at the initial hash size */ |
2821104d | 25 | #define INITIAL_HASH_SIZE 9 |
fc66d213 | 26 | |
2821104d JH |
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)) | |
ba23bbc8 | 31 | |
fc66d213 JH |
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 | ||
c06c7966 | 39 | struct spanhash { |
e31c9f24 LT |
40 | unsigned int hashval; |
41 | unsigned int cnt; | |
c06c7966 JH |
42 | }; |
43 | struct spanhash_top { | |
44 | int alloc_log2; | |
45 | int free; | |
46 | struct spanhash data[FLEX_ARRAY]; | |
47 | }; | |
48 | ||
2821104d | 49 | static struct spanhash *spanhash_find(struct spanhash_top *top, |
e31c9f24 | 50 | unsigned int hashval) |
c06c7966 JH |
51 | { |
52 | int sz = 1 << top->alloc_log2; | |
53 | int bucket = hashval & (sz - 1); | |
54 | while (1) { | |
55 | struct spanhash *h = &(top->data[bucket++]); | |
56 | if (!h->cnt) | |
57 | return NULL; | |
58 | if (h->hashval == hashval) | |
59 | return h; | |
60 | if (sz <= bucket) | |
61 | bucket = 0; | |
62 | } | |
63 | } | |
64 | ||
65 | static struct spanhash_top *spanhash_rehash(struct spanhash_top *orig) | |
66 | { | |
67 | struct spanhash_top *new; | |
68 | int i; | |
69 | int osz = 1 << orig->alloc_log2; | |
70 | int sz = osz << 1; | |
71 | ||
72 | new = xmalloc(sizeof(*orig) + sizeof(struct spanhash) * sz); | |
73 | new->alloc_log2 = orig->alloc_log2 + 1; | |
2821104d | 74 | new->free = INITIAL_FREE(new->alloc_log2); |
c06c7966 JH |
75 | memset(new->data, 0, sizeof(struct spanhash) * sz); |
76 | for (i = 0; i < osz; i++) { | |
77 | struct spanhash *o = &(orig->data[i]); | |
78 | int bucket; | |
79 | if (!o->cnt) | |
80 | continue; | |
81 | bucket = o->hashval & (sz - 1); | |
82 | while (1) { | |
83 | struct spanhash *h = &(new->data[bucket++]); | |
84 | if (!h->cnt) { | |
85 | h->hashval = o->hashval; | |
86 | h->cnt = o->cnt; | |
87 | new->free--; | |
88 | break; | |
89 | } | |
90 | if (sz <= bucket) | |
91 | bucket = 0; | |
92 | } | |
93 | } | |
94 | free(orig); | |
95 | return new; | |
96 | } | |
97 | ||
98 | static struct spanhash_top *add_spanhash(struct spanhash_top *top, | |
e31c9f24 | 99 | unsigned int hashval, int cnt) |
c06c7966 JH |
100 | { |
101 | int bucket, lim; | |
102 | struct spanhash *h; | |
103 | ||
104 | lim = (1 << top->alloc_log2); | |
105 | bucket = hashval & (lim - 1); | |
106 | while (1) { | |
107 | h = &(top->data[bucket++]); | |
108 | if (!h->cnt) { | |
109 | h->hashval = hashval; | |
3c7ceba4 | 110 | h->cnt = cnt; |
c06c7966 JH |
111 | top->free--; |
112 | if (top->free < 0) | |
113 | return spanhash_rehash(top); | |
114 | return top; | |
115 | } | |
116 | if (h->hashval == hashval) { | |
3c7ceba4 | 117 | h->cnt += cnt; |
c06c7966 JH |
118 | return top; |
119 | } | |
120 | if (lim <= bucket) | |
121 | bucket = 0; | |
122 | } | |
123 | } | |
124 | ||
b9905fed | 125 | static struct spanhash_top *hash_chars(struct diff_filespec *one) |
65416758 | 126 | { |
3c7ceba4 | 127 | int i, n; |
e31c9f24 | 128 | unsigned int accum1, accum2, hashval; |
c06c7966 | 129 | struct spanhash_top *hash; |
b9905fed JH |
130 | unsigned char *buf = one->data; |
131 | unsigned int sz = one->size; | |
29a3eefd | 132 | int is_text = !diff_filespec_is_binary(one); |
c06c7966 JH |
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--; |
b9905fed JH |
146 | |
147 | /* Ignore CR in CRLF sequence if text */ | |
148 | if (is_text && c == '\r' && sz && *buf == '\n') | |
149 | continue; | |
150 | ||
e31c9f24 LT |
151 | accum1 = (accum1 << 7) ^ (accum2 >> 25); |
152 | accum2 = (accum2 << 7) ^ (old_1 >> 25); | |
3c7ceba4 LT |
153 | accum1 += c; |
154 | if (++n < 64 && c != '\n') | |
155 | continue; | |
156 | hashval = (accum1 + accum2 * 0x61) % HASHBASE; | |
157 | hash = add_spanhash(hash, hashval, n); | |
158 | n = 0; | |
159 | accum1 = accum2 = 0; | |
65416758 | 160 | } |
c06c7966 | 161 | return hash; |
65416758 JH |
162 | } |
163 | ||
d8c3d03a JH |
164 | int diffcore_count_changes(struct diff_filespec *src, |
165 | struct diff_filespec *dst, | |
c06c7966 JH |
166 | void **src_count_p, |
167 | void **dst_count_p, | |
65416758 JH |
168 | unsigned long delta_limit, |
169 | unsigned long *src_copied, | |
170 | unsigned long *literal_added) | |
171 | { | |
c06c7966 JH |
172 | int i, ssz; |
173 | struct spanhash_top *src_count, *dst_count; | |
ba23bbc8 JH |
174 | unsigned long sc, la; |
175 | ||
c06c7966 JH |
176 | src_count = dst_count = NULL; |
177 | if (src_count_p) | |
178 | src_count = *src_count_p; | |
179 | if (!src_count) { | |
b9905fed | 180 | src_count = hash_chars(src); |
c06c7966 JH |
181 | if (src_count_p) |
182 | *src_count_p = src_count; | |
183 | } | |
184 | if (dst_count_p) | |
185 | dst_count = *dst_count_p; | |
186 | if (!dst_count) { | |
b9905fed | 187 | dst_count = hash_chars(dst); |
c06c7966 JH |
188 | if (dst_count_p) |
189 | *dst_count_p = dst_count; | |
190 | } | |
ba23bbc8 | 191 | sc = la = 0; |
c06c7966 JH |
192 | |
193 | ssz = 1 << src_count->alloc_log2; | |
194 | for (i = 0; i < ssz; i++) { | |
195 | struct spanhash *s = &(src_count->data[i]); | |
196 | struct spanhash *d; | |
197 | unsigned dst_cnt, src_cnt; | |
198 | if (!s->cnt) | |
199 | continue; | |
200 | src_cnt = s->cnt; | |
201 | d = spanhash_find(dst_count, s->hashval); | |
202 | dst_cnt = d ? d->cnt : 0; | |
203 | if (src_cnt < dst_cnt) { | |
204 | la += dst_cnt - src_cnt; | |
205 | sc += src_cnt; | |
ba23bbc8 | 206 | } |
c06c7966 JH |
207 | else |
208 | sc += dst_cnt; | |
ba23bbc8 | 209 | } |
c06c7966 JH |
210 | |
211 | if (!src_count_p) | |
212 | free(src_count); | |
213 | if (!dst_count_p) | |
214 | free(dst_count); | |
ba23bbc8 JH |
215 | *src_copied = sc; |
216 | *literal_added = la; | |
ba23bbc8 | 217 | return 0; |
65416758 | 218 | } |