Revision created by MOE tool push_codebase.

MOE_MIGRATION=


git-svn-id: http://snappy.googlecode.com/svn/trunk@2 03e5f5b5-db94-4691-08a0-1a8bf15f6143

1 files changed, 136 insertions, 0 deletions

diff --git a/snappy-internal.h b/snappy-internal.h
new file mode 100644
index 0000000..3124a50
--- /dev/null
+++ b/snappy-internal.h
@@ -0,0 +1,136 @@
+// Copyright 2008 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+//      Unless required by applicable law or agreed to in writing, software
+//      distributed under the License is distributed on an "AS IS" BASIS,
+//      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//      See the License for the specific language governing permissions and
+//      limitations under the License.
+//
+// Internals shared between the snappy implementation and its unittest.
+
+#ifndef UTIL_SNAPPY_SNAPPY_INTERNAL_H_
+#define UTIL_SNAPPY_SNAPPY_INTERNAL_H_
+
+#include "snappy-stubs-internal.h"
+
+namespace snappy {
+namespace internal {
+
+class WorkingMemory {
+ public:
+  WorkingMemory() : large_table_(NULL) { }
+  ~WorkingMemory() { delete[] large_table_; }
+
+  // Allocates and clears a hash table using memory in "*this",
+  // stores the number of buckets in "*table_size" and returns a pointer to
+  // the base of the hash table.
+  uint16* GetHashTable(size_t input_size, int* table_size);
+
+ private:
+  uint16 small_table_[1<<10];    // 2KB
+  uint16* large_table_;          // Allocated only when needed
+
+  DISALLOW_COPY_AND_ASSIGN(WorkingMemory);
+};
+
+// Flat array compression that does not emit the "uncompressed length"
+// prefix. Compresses "input" string to the "*op" buffer.
+//
+// REQUIRES: "input_length <= kBlockSize"
+// REQUIRES: "op" points to an array of memory that is at least
+// "MaxCompressedLength(input_length)" in size.
+// REQUIRES: All elements in "table[0..table_size-1]" are initialized to zero.
+// REQUIRES: "table_size" is a power of two
+//
+// Returns an "end" pointer into "op" buffer.
+// "end - op" is the compressed size of "input".
+char* CompressFragment(const char* input,
+                       size_t input_length,
+                       char* op,
+                       uint16* table,
+                       const int table_size);
+
+// Return the largest n such that
+//
+//   s1[0,n-1] == s2[0,n-1]
+//   and n <= (s2_limit - s2).
+//
+// Does not read *s2_limit or beyond.
+// Does not read *(s1 + (s2_limit - s2)) or beyond.
+// Requires that s2_limit >= s2.
+//
+// Separate implementation for x86_64, for speed.  Uses the fact that
+// x86_64 is little endian.
+#if defined(ARCH_K8)
+static inline int FindMatchLength(const char* s1,
+                                  const char* s2,
+                                  const char* s2_limit) {
+  DCHECK_GE(s2_limit, s2);
+  int matched = 0;
+
+  // Find out how long the match is. We loop over the data 64 bits at a
+  // time until we find a 64-bit block that doesn't match; then we find
+  // the first non-matching bit and use that to calculate the total
+  // length of the match.
+  while (PREDICT_TRUE(s2 <= s2_limit - 8)) {
+    if (PREDICT_FALSE(UNALIGNED_LOAD64(s2) == UNALIGNED_LOAD64(s1 + matched))) {
+      s2 += 8;
+      matched += 8;
+    } else {
+      // On current (mid-2008) Opteron models there is a 3% more
+      // efficient code sequence to find the first non-matching byte.
+      // However, what follows is ~10% better on Intel Core 2 and newer,
+      // and we expect AMD's bsf instruction to improve.
+      uint64 x = UNALIGNED_LOAD64(s2) ^ UNALIGNED_LOAD64(s1 + matched);
+      int matching_bits = Bits::FindLSBSetNonZero64(x);
+      matched += matching_bits >> 3;
+      return matched;
+    }
+  }
+  while (PREDICT_TRUE(s2 < s2_limit)) {
+    if (PREDICT_TRUE(s1[matched] == *s2)) {
+      ++s2;
+      ++matched;
+    } else {
+      return matched;
+    }
+  }
+  return matched;
+}
+#else
+static inline int FindMatchLength(const char* s1,
+                                  const char* s2,
+                                  const char* s2_limit) {
+  // Implementation based on the x86-64 version, above.
+  DCHECK_GE(s2_limit, s2);
+  int matched = 0;
+
+  while (s2 <= s2_limit - 4 &&
+         UNALIGNED_LOAD32(s2) == UNALIGNED_LOAD32(s1 + matched)) {
+    s2 += 4;
+    matched += 4;
+  }
+  if (LittleEndian::IsLittleEndian() && s2 <= s2_limit - 4) {
+    uint32 x = UNALIGNED_LOAD32(s2) ^ UNALIGNED_LOAD32(s1 + matched);
+    int matching_bits = Bits::FindLSBSetNonZero(x);
+    matched += matching_bits >> 3;
+  } else {
+    while ((s2 < s2_limit) && (s1[matched] == *s2)) {
+      ++s2;
+      ++matched;
+    }
+  }
+  return matched;
+}
+#endif
+
+}  // end namespace internal
+}  // end namespace snappy
+
+#endif  // UTIL_SNAPPY_SNAPPY_INTERNAL_H_