#include "cache.h" #include "diff.h" #include "diffcore.h" /* * Idea here is very simple. * * Almost all data we are interested in are text, but sometimes we have * to deal with binary data. So we cut them into chunks delimited by * LF byte, or 64-byte sequence, whichever comes first, and hash them. * * For those chunks, if the source buffer has more instances of it * than the destination buffer, that means the difference are the * number of bytes not copied from source to destination. If the * counts are the same, everything was copied from source to * destination. If the destination has more, everything was copied, * and destination added more. * * We are doing an approximation so we do not really have to waste * memory by actually storing the sequence. We just hash them into * somewhere around 2^16 hashbuckets and count the occurrences. */ /* Wild guess at the initial hash size */ #define INITIAL_HASH_SIZE 9 /* We leave more room in smaller hash but do not let it * grow to have unused hole too much. */ #define INITIAL_FREE(sz_log2) ((1<<(sz_log2))*(sz_log2-3)/(sz_log2)) /* A prime rather carefully chosen between 2^16..2^17, so that * HASHBASE < INITIAL_FREE(17). We want to keep the maximum hashtable * size under the current 2<<17 maximum, which can hold this many * different values before overflowing to hashtable of size 2<<18. */ #define HASHBASE 107927 struct spanhash { unsigned int hashval; unsigned int cnt; }; struct spanhash_top { int alloc_log2; int free; struct spanhash data[FLEX_ARRAY]; }; static struct spanhash_top *spanhash_rehash(struct spanhash_top *orig) { struct spanhash_top *new; int i; int osz = 1 << orig->alloc_log2; int sz = osz << 1; new = xmalloc(sizeof(*orig) + sizeof(struct spanhash) * sz); new->alloc_log2 = orig->alloc_log2 + 1; new->free = INITIAL_FREE(new->alloc_log2); memset(new->data, 0, sizeof(struct spanhash) * sz); for (i = 0; i < osz; i++) { struct spanhash *o = &(orig->data[i]); int bucket; if (!o->cnt) continue; bucket = o->hashval & (sz - 1); while (1) { struct spanhash *h = &(new->data[bucket++]); if (!h->cnt) { h->hashval = o->hashval; h->cnt = o->cnt; new->free--; break; } if (sz <= bucket) bucket = 0; } } free(orig); return new; } static struct spanhash_top *add_spanhash(struct spanhash_top *top, unsigned int hashval, int cnt) { int bucket, lim; struct spanhash *h; lim = (1 << top->alloc_log2); bucket = hashval & (lim - 1); while (1) { h = &(top->data[bucket++]); if (!h->cnt) { h->hashval = hashval; h->cnt = cnt; top->free--; if (top->free < 0) return spanhash_rehash(top); return top; } if (h->hashval == hashval) { h->cnt += cnt; return top; } if (lim <= bucket) bucket = 0; } } static int spanhash_cmp(const void *a_, const void *b_) { const struct spanhash *a = a_; const struct spanhash *b = b_; /* A count of zero compares at the end.. */ if (!a->cnt) return !b->cnt ? 0 : 1; if (!b->cnt) return -1; return a->hashval < b->hashval ? -1 : a->hashval > b->hashval ? 1 : 0; } static struct spanhash_top *hash_chars(struct diff_filespec *one) { int i, n; unsigned int accum1, accum2, hashval; struct spanhash_top *hash; unsigned char *buf = one->data; unsigned int sz = one->size; int is_text = !diff_filespec_is_binary(one); i = INITIAL_HASH_SIZE; hash = xmalloc(sizeof(*hash) + sizeof(struct spanhash) * (1<alloc_log2 = i; hash->free = INITIAL_FREE(i); memset(hash->data, 0, sizeof(struct spanhash) * (1<> 25); accum2 = (accum2 << 7) ^ (old_1 >> 25); accum1 += c; if (++n < 64 && c != '\n') continue; hashval = (accum1 + accum2 * 0x61) % HASHBASE; hash = add_spanhash(hash, hashval, n); n = 0; accum1 = accum2 = 0; } qsort(hash->data, 1ul << hash->alloc_log2, sizeof(hash->data[0]), spanhash_cmp); return hash; } int diffcore_count_changes(struct diff_filespec *src, struct diff_filespec *dst, void **src_count_p, void **dst_count_p, unsigned long delta_limit, unsigned long *src_copied, unsigned long *literal_added) { struct spanhash *s, *d; struct spanhash_top *src_count, *dst_count; unsigned long sc, la; src_count = dst_count = NULL; if (src_count_p) src_count = *src_count_p; if (!src_count) { src_count = hash_chars(src); if (src_count_p) *src_count_p = src_count; } if (dst_count_p) dst_count = *dst_count_p; if (!dst_count) { dst_count = hash_chars(dst); if (dst_count_p) *dst_count_p = dst_count; } sc = la = 0; s = src_count->data; d = dst_count->data; for (;;) { unsigned dst_cnt, src_cnt; if (!s->cnt) break; /* we checked all in src */ while (d->cnt) { if (d->hashval >= s->hashval) break; la += d->cnt; d++; } src_cnt = s->cnt; dst_cnt = 0; if (d->cnt && d->hashval == s->hashval) { dst_cnt = d->cnt; d++; } if (src_cnt < dst_cnt) { la += dst_cnt - src_cnt; sc += src_cnt; } else sc += dst_cnt; s++; } while (d->cnt) { la += d->cnt; d++; } if (!src_count_p) free(src_count); if (!dst_count_p) free(dst_count); *src_copied = sc; *literal_added = la; return 0; }