clone: the given repository dir should be relative to $PWD
[gitweb.git] / diffcore-delta.c
index 1e6a6911ecc7b9a6b6c28a20db9adea3e1238a2d..7338a40c5964ae6ddfb855465249fc1a2fa5a2a3 100644 (file)
 #include "cache.h"
 #include "diff.h"
 #include "diffcore.h"
-#include "delta.h"
-#include "count-delta.h"
-
-static int diffcore_count_changes_1(void *src, unsigned long src_size,
-                                   void *dst, unsigned long dst_size,
-                                   unsigned long delta_limit,
-                                   unsigned long *src_copied,
-                                   unsigned long *literal_added)
+
+/*
+ * Idea here is very simple.
+ *
+ * We have total of (sz-N+1) N-byte overlapping sequences in buf whose
+ * size is sz.  If the same N-byte sequence appears in both source and
+ * destination, we say the byte that starts that sequence is shared
+ * between them (i.e. copied from source to destination).
+ *
+ * For each possible N-byte sequence, 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.
+ *
+ * The length of the sequence is arbitrarily set to 8 for now.
+ */
+
+/* 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 *spanhash_find(struct spanhash_top *top,
+                                     unsigned int hashval)
 {
-       void *delta;
-       unsigned long delta_size;
-
-       delta = diff_delta(src, src_size,
-                          dst, dst_size,
-                          &delta_size, delta_limit);
-       if (!delta)
-               /* If delta_limit is exceeded, we have too much differences */
-               return -1;
-
-       /* Estimate the edit size by interpreting delta. */
-       if (count_delta(delta, delta_size, src_copied, literal_added)) {
-               free(delta);
-               return -1;
+       int sz = 1 << top->alloc_log2;
+       int bucket = hashval & (sz - 1);
+       while (1) {
+               struct spanhash *h = &(top->data[bucket++]);
+               if (!h->cnt)
+                       return NULL;
+               if (h->hashval == hashval)
+                       return h;
+               if (sz <= bucket)
+                       bucket = 0;
        }
-       free(delta);
-       return 0;
+}
+
+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 struct spanhash_top *hash_chars(unsigned char *buf, unsigned int sz)
+{
+       int i, n;
+       unsigned int accum1, accum2, hashval;
+       struct spanhash_top *hash;
+
+       i = INITIAL_HASH_SIZE;
+       hash = xmalloc(sizeof(*hash) + sizeof(struct spanhash) * (1<<i));
+       hash->alloc_log2 = i;
+       hash->free = INITIAL_FREE(i);
+       memset(hash->data, 0, sizeof(struct spanhash) * (1<<i));
+
+       n = 0;
+       accum1 = accum2 = 0;
+       while (sz) {
+               unsigned int c = *buf++;
+               unsigned int old_1 = accum1;
+               sz--;
+               accum1 = (accum1 << 7) ^ (accum2 >> 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;
+       }
+       return hash;
 }
 
 int diffcore_count_changes(void *src, unsigned long src_size,
                           void *dst, unsigned long dst_size,
+                          void **src_count_p,
+                          void **dst_count_p,
                           unsigned long delta_limit,
                           unsigned long *src_copied,
                           unsigned long *literal_added)
 {
-       return diffcore_count_changes_1(src, src_size,
-                                       dst, dst_size,
-                                       delta_limit,
-                                       src_copied,
-                                       literal_added);
+       int i, ssz;
+       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, src_size);
+               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, dst_size);
+               if (dst_count_p)
+                       *dst_count_p = dst_count;
+       }
+       sc = la = 0;
+
+       ssz = 1 << src_count->alloc_log2;
+       for (i = 0; i < ssz; i++) {
+               struct spanhash *s = &(src_count->data[i]);
+               struct spanhash *d;
+               unsigned dst_cnt, src_cnt;
+               if (!s->cnt)
+                       continue;
+               src_cnt = s->cnt;
+               d = spanhash_find(dst_count, s->hashval);
+               dst_cnt = d ? d->cnt : 0;
+               if (src_cnt < dst_cnt) {
+                       la += dst_cnt - src_cnt;
+                       sc += src_cnt;
+               }
+               else
+                       sc += dst_cnt;
+       }
+
+       if (!src_count_p)
+               free(src_count);
+       if (!dst_count_p)
+               free(dst_count);
+       *src_copied = sc;
+       *literal_added = la;
+       return 0;
 }