whatchanged: Default to DIFF_FORMAT_RAW
[gitweb.git] / diffcore-delta.c
index d03787be65be82b0fcd6dc62dae77013b2576c80..7338a40c5964ae6ddfb855465249fc1a2fa5a2a3 100644 (file)
 #include "diff.h"
 #include "diffcore.h"
 
-struct linehash {
-       unsigned long bytes;
-       unsigned long hash;
+/*
+ * 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 unsigned long hash_extended_line(const unsigned char **buf_p,
-                                       unsigned long left)
+static struct spanhash *spanhash_find(struct spanhash_top *top,
+                                     unsigned int hashval)
 {
-       /* An extended line is zero or more whitespace letters (including LF)
-        * followed by one non whitespace letter followed by zero or more
-        * non LF, and terminated with by a LF (or EOF).
-        */
-       const unsigned char *bol = *buf_p;
-       const unsigned char *buf = bol;
-       unsigned long hashval = 0;
-       while (left) {
-               unsigned c = *buf++;
-               if (!c)
-                       goto binary;
-               left--;
-               if (' ' < c) {
-                       hashval = c;
-                       break;
-               }
-       }
-       while (left) {
-               unsigned c = *buf++;
-               if (!c)
-                       goto binary;
-               left--;
-               if (c == '\n')
-                       break;
-               if (' ' < c)
-                       hashval = hashval * 11 + c;
+       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;
        }
-       *buf_p = buf;
-       return hashval;
-
- binary:
-       *buf_p = NULL;
-       return 0;
 }
 
-static int linehash_compare(const void *a_, const void *b_)
+static struct spanhash_top *spanhash_rehash(struct spanhash_top *orig)
 {
-       struct linehash *a = (struct linehash *) a_;
-       struct linehash *b = (struct linehash *) b_;
-       if (a->hash < b->hash) return -1;
-       if (a->hash > b->hash) return 1;
-       return 0;
+       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 linehash *hash_lines(const unsigned char *buf,
-                                  unsigned long size)
+static struct spanhash_top *add_spanhash(struct spanhash_top *top,
+                                        unsigned int hashval, int cnt)
 {
-       const unsigned char *eobuf = buf + size;
-       struct linehash *line = NULL;
-       int alloc = 0, used = 0;
-
-       while (buf < eobuf) {
-               const unsigned char *ptr = buf;
-               unsigned long hash = hash_extended_line(&buf, eobuf-ptr);
-               if (!buf) {
-                       free(line);
-                       return NULL;
+       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 (alloc <= used) {
-                       alloc = alloc_nr(alloc);
-                       line = xrealloc(line, sizeof(*line) * alloc);
+               if (h->hashval == hashval) {
+                       h->cnt += cnt;
+                       return top;
                }
-               line[used].bytes = buf - ptr;
-               line[used].hash = hash;
-               used++;
+               if (lim <= bucket)
+                       bucket = 0;
        }
-       qsort(line, used, sizeof(*line), linehash_compare);
+}
 
-       /* Terminate the list */
-       if (alloc <= used)
-               line = xrealloc(line, sizeof(*line) * (used+1));
-       line[used].bytes = line[used].hash = 0;
-       return line;
+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)
 {
-       struct linehash *src_lines, *dst_lines;
+       int i, ssz;
+       struct spanhash_top *src_count, *dst_count;
        unsigned long sc, la;
 
-       src_lines = hash_lines(src, src_size);
-       if (!src_lines)
-               return -1;
-       dst_lines = hash_lines(dst, dst_size);
-       if (!dst_lines) {
-               free(src_lines);
-               return -1;
+       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;
-       while (src_lines->bytes && dst_lines->bytes) {
-               int cmp = linehash_compare(src_lines, dst_lines);
-               if (!cmp) {
-                       sc += src_lines->bytes;
-                       src_lines++;
-                       dst_lines++;
-                       continue;
-               }
-               if (cmp < 0) {
-                       src_lines++;
+
+       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;
                }
-               la += dst_lines->bytes;
-               dst_lines++;
-       }
-       while (dst_lines->bytes) {
-               la += dst_lines->bytes;
-               dst_lines++;
+               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;