Improved to avoid a hashtable slowdown for files that don't need

the extra-large hashtable.

diff --git a/dynamic_hash.diff b/dynamic_hash.diff
index f9a41d5..3388bd9 100644 (file)
--- a/dynamic_hash.diff
+++ b/dynamic_hash.diff
@@ -1,9 +1,11 @@
 This patch makes the processing of large really large files more efficient
 by making sure that the sender's hash table is large enough to hold all the
-checksum entries without being overloaded.  Unfortunately, the code adds a
-modulus calculation for (up to) every byte of the source file, which slows
-down the code for normal file sizes (e.g. 4 CPU seconds slower on a Pentium
-III when copying a 65 MB file without very much matching data).
+checksum entries without being overloaded.
+
+Updated to use the current hashtable method when possible, and the new
+hashtable method (which requires a modulus calculation for up to every byte
+of the source file) only on large files that need a larger hashtable size.
+This avoids slowing down files that don't need the extra-large hashtable.
 
 This was updated for the latest codebase from a patch written by Shachar
 Shemesh.
@@ -16,23 +18,25 @@ To use this patch, run these commands for a successful build:
 
 --- old/match.c
 +++ new/match.c
-@@ -40,24 +40,31 @@ static int total_matches;
+@@ -39,29 +39,50 @@ 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)
-+#define SUM2HASH(sum) ((sum)%tablesize)
+ #define SUM2HASH2(s1,s2) (((s1) + (s2)) & 0xFFFF)
+ #define SUM2HASH(sum) SUM2HASH2((sum)&0xFFFF,(sum)>>16)
  
++#define BIG_SUM2HASH(sum) ((sum)%tablesize)
++
  static void build_hash_table(struct sum_struct *s)
  {
++      static uint32 alloc_size;
        int32 i;
-+      uint32 prior_size = tablesize;
  
 -      if (!hash_table) {
 -              hash_table = new_array(int32, TABLESIZE);
@@ -40,30 +44,55 @@ To use this patch, run these commands for a successful build:
 +       * for big files is about 80%.  This number must be odd or s2 will
 +       * not be able to span the entire set. */
 +      tablesize = (uint32)(s->count/8) * 10 + 11;
-+      if (tablesize < 65537)
-+              tablesize = 65537; /* a prime number */
-+      if (tablesize != prior_size) {
++      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]);
 +      memset(hash_table, 0xFF, tablesize * sizeof hash_table[0]);
  
-       for (i = 0; i < s->count; i++) {
-               uint32 t = SUM2HASH(s->sums[i].sum1);
-@@ -165,11 +172,11 @@ static void hash_search(int f,struct sum
+-      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;
++      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;
++              }
+       }
+ }
+ 
+@@ -164,11 +185,16 @@ static void hash_search(int f,struct sum
                                (double)offset, s2 & 0xFFFF, s1 & 0xFFFF);
                }
  
 -              i = hash_table[SUM2HASH2(s1,s2)];
-+              sum = (s1 & 0xffff) | (s2 << 16);
-+              i = hash_table[SUM2HASH(sum)];
-               if (i < 0)
-                       goto null_hash;
+-              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++;