Merge branch 'jc/merge' into next
[gitweb.git] / diffcore-delta.c
index 70bacff83752a6f91b6aa3089374660840e8059a..7338a40c5964ae6ddfb855465249fc1a2fa5a2a3 100644 (file)
  * The length of the sequence is arbitrarily set to 8 for now.
  */
 
-#define HASHBASE 65537 /* next_prime(2^16) */
+/* Wild guess at the initial hash size */
+#define INITIAL_HASH_SIZE 9
 
-static void hash_chars(unsigned char *buf, unsigned long sz, int *count)
+/* 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)
 {
-       unsigned int accum1, accum2, i;
-
-       /* an 8-byte shift register made of accum1 and accum2.  New
-        * bytes come at LSB of accum2, and shifted up to accum1
-        */
-       for (i = accum1 = accum2 = 0; i < 7; i++, sz--) {
-               accum1 = (accum1 << 8) | (accum2 >> 24);
-               accum2 = (accum2 << 8) | *buf++;
+       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;
        }
+}
+
+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) {
-               accum1 = (accum1 << 8) | (accum2 >> 24);
-               accum2 = (accum2 << 8) | *buf++;
-               /* We want something that hashes permuted byte
-                * sequences nicely; simpler hash like (accum1 ^
-                * accum2) does not perform as well.
-                */
-               i = (accum1 + accum2 * 0x61) % HASHBASE;
-               count[i]++;
+               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)
 {
-       int *src_count, *dst_count, i;
+       int i, ssz;
+       struct spanhash_top *src_count, *dst_count;
        unsigned long sc, la;
 
-       if (src_size < 8 || dst_size < 8)
-               return -1;
-
-       src_count = xcalloc(HASHBASE * 2, sizeof(int));
-       dst_count = src_count + HASHBASE;
-       hash_chars(src, src_size, src_count);
-       hash_chars(dst, dst_size, dst_count);
-
+       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;
-       for (i = 0; i < HASHBASE; i++) {
-               if (src_count[i] < dst_count[i]) {
-                       la += dst_count[i] - src_count[i];
-                       sc += src_count[i];
+
+       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 /* i.e. if (dst_count[i] <= src_count[i]) */
-                       sc += dst_count[i];
+               else
+                       sc += dst_cnt;
        }
+
+       if (!src_count_p)
+               free(src_count);
+       if (!dst_count_p)
+               free(dst_count);
        *src_copied = sc;
        *literal_added = la;
-       free(src_count);
        return 0;
 }