The Tor Browser: gfx/skia/trunk/include/core/SkChecksum.h@129ffea94266 (annotated)

gfx/skia/trunk/include/core/SkChecksum.h@129ffea94266 (annotated)

gfx/skia/trunk/include/core/SkChecksum.h

Sat, 03 Jan 2015 20:18:00 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Sat, 03 Jan 2015 20:18:00 +0100
branch: TOR_BUG_3246
changeset 7: 129ffea94266
permissions: -rw-r--r--

Conditionally enable double key logic according to:
private browsing mode or privacy.thirdparty.isolate preference and
implement in GetCookieStringCommon and FindCookie where it counts...
With some reservations of how to convince FindCookie users to test
condition and pass a nullptr when disabling double key logic.

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef SkChecksum_DEFINED
 #define SkChecksum_DEFINED
 #include "SkTypes.h"
 /**
  *  Computes a 32bit checksum from a blob of 32bit aligned data. This is meant
  *  to be very very fast, as it is used internally by the font cache, in
  *  conjuction with the entire raw key. This algorithm does not generate
  *  unique values as well as others (e.g. MD5) but it performs much faster.
  *  Skia's use cases can survive non-unique values (since the entire key is
  *  always available). Clients should only be used in circumstances where speed
  *  over uniqueness is at a premium.
  */
 class SkChecksum : SkNoncopyable {
 private:
     /*
      *  Our Rotate and Mash helpers are meant to automatically do the right
      *  thing depending if sizeof(uintptr_t) is 4 or 8.
      */
     enum {
         ROTR = 17,
         ROTL = sizeof(uintptr_t) * 8 - ROTR,
         HALFBITS = sizeof(uintptr_t) * 4
     };
     static inline uintptr_t Mash(uintptr_t total, uintptr_t value) {
         return ((total >> ROTR) | (total << ROTL)) ^ value;
     }
 public:
     /**
      * Calculate 32-bit Murmur hash (murmur3).
      * This should take 2-3x longer than SkChecksum::Compute, but is a considerably better hash.
      * See en.wikipedia.org/wiki/MurmurHash.
      *
      *  @param data Memory address of the data block to be processed. Must be 32-bit aligned.
      *  @param size Size of the data block in bytes. Must be a multiple of 4.
      *  @param seed Initial hash seed. (optional)
      *  @return hash result
      */
     static uint32_t Murmur3(const uint32_t* data, size_t bytes, uint32_t seed=0) {
         SkASSERT(SkIsAlign4(bytes));
         const size_t words = bytes/4;
         uint32_t hash = seed;
         for (size_t i = 0; i < words; i++) {
             uint32_t k = data[i];
             k *= 0xcc9e2d51;
             k = (k << 15) | (k >> 17);
             k *= 0x1b873593;
             hash ^= k;
             hash = (hash << 13) | (hash >> 19);
             hash *= 5;
             hash += 0xe6546b64;
         }
         hash ^= bytes;
         hash ^= hash >> 16;
         hash *= 0x85ebca6b;
         hash ^= hash >> 13;
         hash *= 0xc2b2ae35;
         hash ^= hash >> 16;
         return hash;
     }
     /**
      *  Compute a 32-bit checksum for a given data block
      *
      *  WARNING: this algorithm is tuned for efficiency, not backward/forward
      *  compatibility.  It may change at any time, so a checksum generated with
      *  one version of the Skia code may not match a checksum generated with
      *  a different version of the Skia code.
      *
      *  @param data Memory address of the data block to be processed. Must be
      *              32-bit aligned.
      *  @param size Size of the data block in bytes. Must be a multiple of 4.
      *  @return checksum result
      */
     static uint32_t Compute(const uint32_t* data, size_t size) {
         SkASSERT(SkIsAlign4(size));
         /*
          *  We want to let the compiler use 32bit or 64bit addressing and math
          *  so we use uintptr_t as our magic type. This makes the code a little
          *  more obscure (we can't hard-code 32 or 64 anywhere, but have to use
          *  sizeof()).
          */
         uintptr_t result = 0;
         const uintptr_t* ptr = reinterpret_cast<const uintptr_t*>(data);
         /*
          *  count the number of quad element chunks. This takes into account
          *  if we're on a 32bit or 64bit arch, since we use sizeof(uintptr_t)
          *  to compute how much to shift-down the size.
          */
         size_t n4 = size / (sizeof(uintptr_t) << 2);
         for (size_t i = 0; i < n4; ++i) {
             result = Mash(result, *ptr++);
             result = Mash(result, *ptr++);
             result = Mash(result, *ptr++);
             result = Mash(result, *ptr++);
         }
         size &= ((sizeof(uintptr_t) << 2) - 1);
         data = reinterpret_cast<const uint32_t*>(ptr);
         const uint32_t* stop = data + (size >> 2);
         while (data < stop) {
             result = Mash(result, *data++);
         }
         /*
          *  smash us down to 32bits if we were 64. Note that when uintptr_t is
          *  32bits, this code-path should go away, but I still got a warning
          *  when I wrote
          *      result ^= result >> 32;
          *  since >>32 is undefined for 32bit ints, hence the wacky HALFBITS
          *  define.
          */
         if (8 == sizeof(result)) {
             result ^= result >> HALFBITS;
         }
         return static_cast<uint32_t>(result);
     }
 };
 #endif

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gfx/skia/trunk/include/core/SkChecksum.h@129ffea94266 (annotated)

gfx/skia/trunk/include/core/SkChecksum.h