The Tor Browser: other-licenses/snappy/src/snappy-internal.h@97036ab72558 (annotated)

other-licenses/snappy/src/snappy-internal.h@97036ab72558 (annotated)

other-licenses/snappy/src/snappy-internal.h

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 // Copyright 2008 Google Inc. All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 // copyright notice, this list of conditions and the following disclaimer
 // in the documentation and/or other materials provided with the
 // distribution.
 //     * Neither the name of Google Inc. nor the names of its
 // contributors may be used to endorse or promote products derived from
 // this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 //
 // 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_

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