config option log.showroot to show the diff of root commits

[git.git] / diff-delta.c

diff --git a/diff-delta.c b/diff-delta.c
index 35e517d2d79002214988b57b476faa29f8292394..fa16d06c8d1e85a458428c673cb2f589857f5424 100644 (file)
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -22,6 +22,7 @@
 #include <string.h>
 #include "delta.h"
 
+#include "git-compat-util.h"
 
 /* maximum hash entry list for the same hash bucket */
 #define HASH_LIMIT 64
@@ -131,33 +132,35 @@ struct delta_index {
        const void *src_buf;
        unsigned long src_size;
        unsigned int hash_mask;
-       struct index_entry *hash[0];
+       struct index_entry *hash[FLEX_ARRAY];
 };
 
 struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
 {
-       unsigned int i, hsize, hmask, entries, *hash_count;
+       unsigned int i, hsize, hmask, entries, prev_val, *hash_count;
        const unsigned char *data, *buffer = buf;
        struct delta_index *index;
        struct index_entry *entry, **hash;
        void *mem;
+       unsigned long memsize;
 
        if (!buf || !bufsize)
                return NULL;
 
        /* Determine index hash size.  Note that indexing skips the
-          first byte to allow for optimizing the rabin polynomial
+          first byte to allow for optimizing the Rabin's polynomial
           initialization in create_delta(). */
        entries = (bufsize - 1)  / RABIN_WINDOW;
        hsize = entries / 4;
-       for (i = 4; (1 << i) < hsize && i < 31; i++);
+       for (i = 4; (1u << i) < hsize && i < 31; i++);
        hsize = 1 << i;
        hmask = hsize - 1;
 
        /* allocate lookup index */
-       mem = malloc(sizeof(*index) +
-                    sizeof(*hash) * hsize +
-                    sizeof(*entry) * entries);
+       memsize = sizeof(*index) +
+                 sizeof(*hash) * hsize +
+                 sizeof(*entry) * entries;
+       mem = malloc(memsize);
        if (!mem)
                return NULL;
        index = mem;
@@ -179,23 +182,30 @@ struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
        }
 
        /* then populate the index */
-       data = buffer + entries * RABIN_WINDOW - RABIN_WINDOW;
-       while (data >= buffer) {
+       prev_val = ~0;
+       for (data = buffer + entries * RABIN_WINDOW - RABIN_WINDOW;
+            data >= buffer;
+            data -= RABIN_WINDOW) {
                unsigned int val = 0;
                for (i = 1; i <= RABIN_WINDOW; i++)
                        val = ((val << 8) | data[i]) ^ T[val >> RABIN_SHIFT];
-               i = val & hmask;
-               entry->ptr = data + RABIN_WINDOW;
-               entry->val = val;
-               entry->next = hash[i];
-               hash[i] = entry++;
-               hash_count[i]++;
-               data -= RABIN_WINDOW;
+               if (val == prev_val) {
+                       /* keep the lowest of consecutive identical blocks */
+                       entry[-1].ptr = data + RABIN_WINDOW;
+               } else {
+                       prev_val = val;
+                       i = val & hmask;
+                       entry->ptr = data + RABIN_WINDOW;
+                       entry->val = val;
+                       entry->next = hash[i];
+                       hash[i] = entry++;
+                       hash_count[i]++;
+               }
        }
 
        /*
         * Determine a limit on the number of entries in the same hash
-        * bucket.  This guard us against patological data sets causing
+        * bucket.  This guards us against pathological data sets causing
         * really bad hash distribution with most entries in the same hash
         * bucket that would bring us to O(m*n) computing costs (m and n
         * corresponding to reference and target buffer sizes).
@@ -230,7 +240,7 @@ void free_delta_index(struct delta_index *index)
 
 /*
  * The maximum size for any opcode sequence, including the initial header
- * plus rabin window plus biggest copy.
+ * plus Rabin window plus biggest copy.
  */
 #define MAX_OP_SIZE    (5 + 5 + 1 + RABIN_WINDOW + 7)
 
@@ -239,7 +249,7 @@ create_delta(const struct delta_index *index,
             const void *trg_buf, unsigned long trg_size,
             unsigned long *delta_size, unsigned long max_size)
 {
-       unsigned int i, outpos, outsize, hash_mask, val;
+       unsigned int i, outpos, outsize, val;
        int inscnt;
        const unsigned char *ref_data, *ref_top, *data, *top;
        unsigned char *out;
@@ -274,8 +284,7 @@ create_delta(const struct delta_index *index,
        ref_data = index->src_buf;
        ref_top = ref_data + index->src_size;
        data = trg_buf;
-       top = trg_buf + trg_size;
-       hash_mask = index->hash_mask;
+       top = (const unsigned char *) trg_buf + trg_size;
 
        outpos++;
        val = 0;
@@ -290,7 +299,7 @@ create_delta(const struct delta_index *index,
                struct index_entry *entry;
                val ^= U[data[-RABIN_WINDOW]];
                val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
-               i = val & hash_mask;
+               i = val & index->hash_mask;
                for (entry = index->hash[i]; entry; entry = entry->next) {
                        const unsigned char *ref = entry->ptr;
                        const unsigned char *src = data;
@@ -383,7 +392,7 @@ create_delta(const struct delta_index *index,
                                outsize = max_size + MAX_OP_SIZE + 1;
                        if (max_size && outpos > max_size)
                                break;
-                       out = realloc(out, outsize);
+                       out = xrealloc(out, outsize);
                        if (!out) {
                                free(tmp);
                                return NULL;