X-Git-Url: https://git.octo.it/?p=git.git;a=blobdiff_plain;f=diffcore-delta.c;h=7338a40c5964ae6ddfb855465249fc1a2fa5a2a3;hp=1e6a6911ecc7b9a6b6c28a20db9adea3e1238a2d;hb=HEAD;hpb=21dbe12c76e43735dc623067c1b09ef43519d9fc

diff --git a/diffcore-delta.c b/diffcore-delta.c
index 1e6a6911..7338a40c 100644
--- a/diffcore-delta.c
+++ b/diffcore-delta.c
@@ -1,43 +1,213 @@
 #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;
 }