| 1 | #include "git-compat-util.h" |
| 2 | #include "diffcore.h" |
| 3 | |
| 4 | /* |
| 5 | * Idea here is very simple. |
| 6 | * |
| 7 | * Almost all data we are interested in are text, but sometimes we have |
| 8 | * to deal with binary data. So we cut them into chunks delimited by |
| 9 | * LF byte, or 64-byte sequence, whichever comes first, and hash them. |
| 10 | * |
| 11 | * For those chunks, if the source buffer has more instances of it |
| 12 | * than the destination buffer, that means the difference are the |
| 13 | * number of bytes not copied from source to destination. If the |
| 14 | * counts are the same, everything was copied from source to |
| 15 | * destination. If the destination has more, everything was copied, |
| 16 | * and destination added more. |
| 17 | * |
| 18 | * We are doing an approximation so we do not really have to waste |
| 19 | * memory by actually storing the sequence. We just hash them into |
| 20 | * somewhere around 2^16 hashbuckets and count the occurrences. |
| 21 | */ |
| 22 | |
| 23 | /* Wild guess at the initial hash size */ |
| 24 | #define INITIAL_HASH_SIZE 9 |
| 25 | |
| 26 | /* We leave more room in smaller hash but do not let it |
| 27 | * grow to have unused hole too much. |
| 28 | */ |
| 29 | #define INITIAL_FREE(sz_log2) ((1<<(sz_log2))*(sz_log2-3)/(sz_log2)) |
| 30 | |
| 31 | /* A prime rather carefully chosen between 2^16..2^17, so that |
| 32 | * HASHBASE < INITIAL_FREE(17). We want to keep the maximum hashtable |
| 33 | * size under the current 2<<17 maximum, which can hold this many |
| 34 | * different values before overflowing to hashtable of size 2<<18. |
| 35 | */ |
| 36 | #define HASHBASE 107927 |
| 37 | |
| 38 | struct spanhash { |
| 39 | unsigned int hashval; |
| 40 | unsigned int cnt; |
| 41 | }; |
| 42 | struct spanhash_top { |
| 43 | int alloc_log2; |
| 44 | int free; |
| 45 | struct spanhash data[FLEX_ARRAY]; |
| 46 | }; |
| 47 | |
| 48 | static struct spanhash_top *spanhash_rehash(struct spanhash_top *orig) |
| 49 | { |
| 50 | struct spanhash_top *new_spanhash; |
| 51 | int i; |
| 52 | int osz = 1 << orig->alloc_log2; |
| 53 | int sz = osz << 1; |
| 54 | |
| 55 | new_spanhash = xmalloc(st_add(sizeof(*orig), |
| 56 | st_mult(sizeof(struct spanhash), sz))); |
| 57 | new_spanhash->alloc_log2 = orig->alloc_log2 + 1; |
| 58 | new_spanhash->free = INITIAL_FREE(new_spanhash->alloc_log2); |
| 59 | MEMZERO_ARRAY(new_spanhash->data, 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_spanhash->data[bucket++]); |
| 68 | if (!h->cnt) { |
| 69 | h->hashval = o->hashval; |
| 70 | h->cnt = o->cnt; |
| 71 | new_spanhash->free--; |
| 72 | break; |
| 73 | } |
| 74 | if (sz <= bucket) |
| 75 | bucket = 0; |
| 76 | } |
| 77 | } |
| 78 | free(orig); |
| 79 | return new_spanhash; |
| 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 repository *r, |
| 124 | struct diff_filespec *one) |
| 125 | { |
| 126 | int i, n; |
| 127 | unsigned int accum1, accum2, hashval; |
| 128 | struct spanhash_top *hash; |
| 129 | unsigned char *buf = one->data; |
| 130 | unsigned int sz = one->size; |
| 131 | int is_text = !diff_filespec_is_binary(r, one); |
| 132 | |
| 133 | i = INITIAL_HASH_SIZE; |
| 134 | hash = xmalloc(st_add(sizeof(*hash), |
| 135 | st_mult(sizeof(struct spanhash), (size_t)1 << i))); |
| 136 | hash->alloc_log2 = i; |
| 137 | hash->free = INITIAL_FREE(i); |
| 138 | MEMZERO_ARRAY(hash->data, (size_t)1 << i); |
| 139 | |
| 140 | n = 0; |
| 141 | accum1 = accum2 = 0; |
| 142 | while (sz) { |
| 143 | unsigned int c = *buf++; |
| 144 | unsigned int old_1 = accum1; |
| 145 | sz--; |
| 146 | |
| 147 | /* Ignore CR in CRLF sequence if text */ |
| 148 | if (is_text && c == '\r' && sz && *buf == '\n') |
| 149 | continue; |
| 150 | |
| 151 | accum1 = (accum1 << 7) ^ (accum2 >> 25); |
| 152 | accum2 = (accum2 << 7) ^ (old_1 >> 25); |
| 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; |
| 160 | } |
| 161 | if (n > 0) { |
| 162 | hashval = (accum1 + accum2 * 0x61) % HASHBASE; |
| 163 | hash = add_spanhash(hash, hashval, n); |
| 164 | } |
| 165 | QSORT(hash->data, (size_t)1ul << hash->alloc_log2, spanhash_cmp); |
| 166 | return hash; |
| 167 | } |
| 168 | |
| 169 | int diffcore_count_changes(struct repository *r, |
| 170 | struct diff_filespec *src, |
| 171 | struct diff_filespec *dst, |
| 172 | void **src_count_p, |
| 173 | void **dst_count_p, |
| 174 | unsigned long *src_copied, |
| 175 | unsigned long *literal_added) |
| 176 | { |
| 177 | struct spanhash *s, *d; |
| 178 | struct spanhash_top *src_count, *dst_count; |
| 179 | unsigned long sc, la; |
| 180 | |
| 181 | src_count = dst_count = NULL; |
| 182 | if (src_count_p) |
| 183 | src_count = *src_count_p; |
| 184 | if (!src_count) { |
| 185 | src_count = hash_chars(r, src); |
| 186 | if (src_count_p) |
| 187 | *src_count_p = src_count; |
| 188 | } |
| 189 | if (dst_count_p) |
| 190 | dst_count = *dst_count_p; |
| 191 | if (!dst_count) { |
| 192 | dst_count = hash_chars(r, dst); |
| 193 | if (dst_count_p) |
| 194 | *dst_count_p = dst_count; |
| 195 | } |
| 196 | sc = la = 0; |
| 197 | |
| 198 | s = src_count->data; |
| 199 | d = dst_count->data; |
| 200 | for (;;) { |
| 201 | unsigned dst_cnt, src_cnt; |
| 202 | if (!s->cnt) |
| 203 | break; /* we checked all in src */ |
| 204 | while (d->cnt) { |
| 205 | if (d->hashval >= s->hashval) |
| 206 | break; |
| 207 | la += d->cnt; |
| 208 | d++; |
| 209 | } |
| 210 | src_cnt = s->cnt; |
| 211 | dst_cnt = 0; |
| 212 | if (d->cnt && d->hashval == s->hashval) { |
| 213 | dst_cnt = d->cnt; |
| 214 | d++; |
| 215 | } |
| 216 | if (src_cnt < dst_cnt) { |
| 217 | la += dst_cnt - src_cnt; |
| 218 | sc += src_cnt; |
| 219 | } |
| 220 | else |
| 221 | sc += dst_cnt; |
| 222 | s++; |
| 223 | } |
| 224 | while (d->cnt) { |
| 225 | la += d->cnt; |
| 226 | d++; |
| 227 | } |
| 228 | |
| 229 | if (!src_count_p) |
| 230 | free(src_count); |
| 231 | if (!dst_count_p) |
| 232 | free(dst_count); |
| 233 | *src_copied = sc; |
| 234 | *literal_added = la; |
| 235 | return 0; |
| 236 | } |