Load more dictionary positions into table if empty

If the hash table is empty load positions into the hash table
that we would otherwise skip.

| Level | Data Set     | Improvement |
|-------|--------------|-------------|
| 1     | github       | 0.44%       |
| 1     | hg-changelog | 0.13%       |
| 1     | hg-commands  | 1.28%       |
| 1     | hg-manifest  | 0.70%       |
| 3     | github       | 0.74%       |
| 3     | hg-changelog | 0.87%       |
| 3     | hg-commands  | 1.74%       |
| 3     | hg-manifest  | 0.23%       |

diff --git a/lib/compress/zstd_double_fast.c b/lib/compress/zstd_double_fast.c
index fee5127c352bfde78f726e60e7a631dbb3f2b2e4..a6d8ad889eae6fd72b4c6f6b7fd73af97ab0c1c6 100644 (file)
--- a/lib/compress/zstd_double_fast.c
+++ b/lib/compress/zstd_double_fast.c
@@ -21,12 +21,23 @@ void ZSTD_fillDoubleHashTable(ZSTD_CCtx* cctx, const void* end, const U32 mls)
     const BYTE* const base = cctx->base;
     const BYTE* ip = base + cctx->nextToUpdate;
     const BYTE* const iend = ((const BYTE*)end) - HASH_READ_SIZE;
-    const size_t fastHashFillStep = 3;
-
-    while(ip <= iend) {
-        hashSmall[ZSTD_hashPtr(ip, hBitsS, mls)] = (U32)(ip - base);
-        hashLarge[ZSTD_hashPtr(ip, hBitsL, 8)] = (U32)(ip - base);
-        ip += fastHashFillStep;
+    const U32 fastHashFillStep = 3;
+
+    /* Always insert every fastHashFillStep position into the hash tables.
+     * Insert the other positions into the large hash table if their entry
+     * is empty.
+     */
+    for (; ip + fastHashFillStep - 1 <= iend; ip += fastHashFillStep) {
+        U32 const current = (U32)(ip - base);
+        U32 i;
+        for (i = 0; i < fastHashFillStep; ++i) {
+            size_t const smHash = ZSTD_hashPtr(ip + i, hBitsS, mls);
+            size_t const lgHash = ZSTD_hashPtr(ip + i, hBitsL, 8);
+            if (i == 0)
+                hashSmall[smHash] = current + i;
+            if (i == 0 || hashLarge[lgHash] == 0)
+                hashLarge[lgHash] = current + i;
+        }
     }
 }
 

diff --git a/lib/compress/zstd_fast.c b/lib/compress/zstd_fast.c
index 7b56c3d6adb69971b47f28b39b6eab6c21e39654..6497a2d8b581255595970eea001ea95f30d8b429 100644 (file)
--- a/lib/compress/zstd_fast.c
+++ b/lib/compress/zstd_fast.c
@@ -19,11 +19,19 @@ void ZSTD_fillHashTable (ZSTD_CCtx* zc, const void* end, const U32 mls)
     const BYTE* const base = zc->base;
     const BYTE* ip = base + zc->nextToUpdate;
     const BYTE* const iend = ((const BYTE*)end) - HASH_READ_SIZE;
-    const size_t fastHashFillStep = 3;
-
-    while(ip <= iend) {
-        hashTable[ZSTD_hashPtr(ip, hBits, mls)] = (U32)(ip - base);
-        ip += fastHashFillStep;
+    const U32 fastHashFillStep = 3;
+
+    /* Always insert every fastHashFillStep position into the hash table.
+     * Insert the other positions if their hash entry is empty.
+     */
+    for (; ip + fastHashFillStep - 1 <= iend; ip += fastHashFillStep) {
+        U32 const current = (U32)(ip - base);
+        U32 i;
+        for (i = 0; i < fastHashFillStep; ++i) {
+            size_t const hash = ZSTD_hashPtr(ip + i, hBits, mls);
+            if (i == 0 || hashTable[hash] == 0)
+                hashTable[hash] = current + i;
+        }
     }
 }