Switching over to a dynamic hash method for really large files.

This code has been reported to be better for large files than the
file-chunking code that was included in pre3.

diff --git a/match.c b/match.c
index 79e591a..17d9181 100644 (file)
--- a/match.c
+++ b/match.c
@@ -39,40 +39,51 @@ static int total_matches;
 
 extern struct stats stats;
 
-#define TABLESIZE (1<<16)
+#define TRADITIONAL_TABLESIZE (1<<16)
 
+static uint32 tablesize;
 static int32 *hash_table;
 
 #define SUM2HASH2(s1,s2) (((s1) + (s2)) & 0xFFFF)
 #define SUM2HASH(sum) SUM2HASH2((sum)&0xFFFF,(sum)>>16)
 
-static int32 build_hash_table(struct sum_struct *s, int32 start)
-{
-       int32 i, end = s->count;
+#define BIG_SUM2HASH(sum) ((sum)%tablesize)
 
-       if (!hash_table) {
-               hash_table = new_array(int32, TABLESIZE);
+static void build_hash_table(struct sum_struct *s)
+{
+       static uint32 alloc_size;
+       int32 i;
+
+       /* Dynamically calculate the hash table size so that the hash load
+        * for big files is about 80%.  A number greater than the traditional
+        * size must be odd or s2 will not be able to span the entire set. */
+       tablesize = (uint32)(s->count/8) * 10 + 11;
+       if (tablesize < TRADITIONAL_TABLESIZE)
+               tablesize = TRADITIONAL_TABLESIZE;
+       if (tablesize > alloc_size || tablesize < alloc_size - 16*1024) {
+               if (hash_table)
+                       free(hash_table);
+               hash_table = new_array(int32, tablesize);
                if (!hash_table)
                        out_of_memory("build_hash_table");
+               alloc_size = tablesize;
        }
 
-       memset(hash_table, 0xFF, TABLESIZE * sizeof hash_table[0]);
-
-       if (end - start > TABLESIZE*8/10)
-               end = start + TABLESIZE*8/10;
-
-       for (i = start; i < end; i++) {
-               uint32 t = SUM2HASH(s->sums[i].sum1);
-               s->sums[i].chain = hash_table[t];
-               hash_table[t] = i;
-       }
+       memset(hash_table, 0xFF, tablesize * sizeof hash_table[0]);
 
-       if (verbose > 2) {
-               rprintf(FINFO, "built hash table for entries %ld - %ld\n",
-                       (long)start, (long)end - 1);
+       if (tablesize == TRADITIONAL_TABLESIZE) {
+               for (i = 0; i < s->count; i++) {
+                       uint32 t = SUM2HASH(s->sums[i].sum1);
+                       s->sums[i].chain = hash_table[t];
+                       hash_table[t] = i;
+               }
+       } else {
+               for (i = 0; i < s->count; i++) {
+                       uint32 t = BIG_SUM2HASH(s->sums[i].sum1);
+                       s->sums[i].chain = hash_table[t];
+                       hash_table[t] = i;
+               }
        }
-
-       return end;
 }
 
 
@@ -130,8 +141,8 @@ static void matched(int f, struct sum_struct *s, struct map_struct *buf,
 static void hash_search(int f,struct sum_struct *s,
                        struct map_struct *buf, OFF_T len)
 {
-       OFF_T offset, end, reset = 0;
-       int32 k, want_i, backup, sum_pos = 0;
+       OFF_T offset, end;
+       int32 k, want_i, backup;
        char sum2[SUM_LENGTH];
        uint32 s1, s2, sum;
        int more;
@@ -169,24 +180,21 @@ static void hash_search(int f,struct sum_struct *s,
                int done_csum2 = 0;
                int32 i;
 
-               if (offset >= reset) {
-                       sum_pos = build_hash_table(s, sum_pos);
-                       if (sum_pos == s->count)
-                               reset = len;
-                       else
-                               reset = sum_pos * s->blength;
-               }
-
                if (verbose > 4) {
                        rprintf(FINFO, "offset=%.0f sum=%04x%04x\n",
                                (double)offset, s2 & 0xFFFF, s1 & 0xFFFF);
                }
 
-               i = hash_table[SUM2HASH2(s1,s2)];
-               if (i < 0)
-                       goto null_hash;
+               if (tablesize == TRADITIONAL_TABLESIZE) {
+                       if ((i = hash_table[SUM2HASH2(s1,s2)]) < 0)
+                               goto null_hash;
+                       sum = (s1 & 0xffff) | (s2 << 16);
+               } else {
+                       sum = (s1 & 0xffff) | (s2 << 16);
+                       if ((i = hash_table[BIG_SUM2HASH(sum)]) < 0)
+                               goto null_hash;
+               }
 
-               sum = (s1 & 0xffff) | (s2 << 16);
                hash_hits++;
                do {
                        int32 l;
@@ -354,6 +362,11 @@ void match_sums(int f, struct sum_struct *s, struct map_struct *buf, OFF_T len)
        }
 
        if (len > 0 && s->count > 0) {
+               build_hash_table(s);
+
+               if (verbose > 2)
+                       rprintf(FINFO,"built hash table\n");
+
                hash_search(f, s, buf, len);
 
                if (verbose > 2)