Use CityHash for tiles

This reduces the level of collisions between hash buckets between
different image tiles.

.gitmodules

@@ -66,3 +66,6 @@
 [submodule "src/tga"]
 	path = src/tga
 	url = https://github.com/aseprite/tga.git
+[submodule "third_party/cityhash"]
+	path = third_party/cityhash
+	url = https://github.com/aseprite/cityhash.git

docs/LICENSES.md

@@ -53,6 +53,30 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 ```
 
+# [cityhash](https://github.com/google/cityhash)
+
+```
+Copyright (c) 2011 Google, Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+```
+
 # [cmark](https://github.com/jgm/cmark)
 
 ```

src/doc/CMakeLists.txt

@@ -1,5 +1,5 @@
 # Aseprite Document Library
-# Copyright (C) 2019-2020 Igara Studio S.A.
+# Copyright (C) 2019-2021 Igara Studio S.A.
 # Copyright (C) 2001-2018 David Capello
 
 if(WIN32)
@@ -80,4 +80,5 @@ add_library(doc-lib
 target_link_libraries(doc-lib
   laf-gfx
   laf-base
-  fixmath-lib)
+  fixmath-lib
+  cityhash)

src/doc/image_impl.h

@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2016  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -72,6 +72,9 @@ namespace doc {
       else
         m_buffer->resizeIfNecessary(required_size);
 
+      std::fill(m_buffer->buffer(),
+                m_buffer->buffer()+required_size, 0);
+
       m_rows = (address_t*)m_buffer->buffer();
       m_bits = (address_t)(m_buffer->buffer() + for_rows);
 

src/doc/primitives.cpp

@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2018-2020 Igara Studio S.A.
+// Copyright (c) 2018-2021 Igara Studio S.A.
 // Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -20,6 +20,8 @@
 #include "doc/tile.h"
 #include "gfx/region.h"
 
+#include <city.h>
+
 #include <stdexcept>
 
 namespace doc {
@@ -442,21 +444,30 @@ template <typename ImageTraits, uint32_t Mask>
 static uint32_t calculate_image_hash_templ(const Image* image,
                                            const gfx::Rect& bounds)
 {
-  uint32_t hash = 0;
-  for (int y=0; y<bounds.h; ++y) {
-    auto p = (typename ImageTraits::address_t)image->getPixelAddress(bounds.x, bounds.y+y);
-    for (int x=0; x<bounds.w; ++x, ++p) {
-      uint32_t value = *p;
-      uint32_t mask = Mask;
-      while (mask) {
-        hash += value & mask & 0xff;
-        hash <<= 1;
-        value >>= 8;
-        mask >>= 8;
-      }
-    }
+#if defined(__LP64__) || defined(__x86_64__) || defined(_WIN64)
+  #define CITYHASH(buf, len) (CityHash64(buf, len) & 0xffffffff)
+  static_assert(sizeof(void*) == 8, "This CPU is not 64-bit");
+#else
+  #define CITYHASH(buf, len) CityHash32(buf, len)
+  static_assert(sizeof(void*) == 4, "This CPU is not 32-bit");
+#endif
+
+  const uint32_t rowlen = ImageTraits::getRowStrideBytes(bounds.w);
+  const uint32_t len = rowlen * bounds.h;
+  if (bounds == image->bounds()) {
+    return CITYHASH((const char*)image->getPixelAddress(0, 0), len);
+  }
+  else {
+    ASSERT(false);              // TODO not used at this moment
+
+    std::vector<uint8_t> buf(len);
+    uint8_t* dst = &buf[0];
+    for (int y=0; y<bounds.h; ++y, dst+=rowlen) {
+      auto src = image->getPixelAddress(bounds.x, bounds.y+y);
+      std::copy(dst, dst+rowlen, src);
+    }
+    return CITYHASH((const char*)&buf[0], buf.size());
   }
-  return hash;
 }
 
 uint32_t calculate_image_hash(const Image* img, const gfx::Rect& bounds)
@@ -467,18 +478,8 @@ uint32_t calculate_image_hash(const Image* img, const gfx::Rect& bounds)
     case IMAGE_INDEXED:   return calculate_image_hash_templ<IndexedTraits, 0xff>(img, bounds);
     case IMAGE_BITMAP:    return calculate_image_hash_templ<BitmapTraits, 1>(img, bounds);
   }
-
-  uint32_t hash = 0;
-  for (int y=0; y<bounds.h; ++y) {
-    int bytes = img->getRowStrideSize(bounds.w);
-    uint8_t* p = img->getPixelAddress(bounds.x, bounds.y+y);
-    while (bytes-- > 0) {
-      hash += *p;
-      hash <<= 1;
-      ++p;
-    }
-  }
-  return hash;
+  ASSERT(false);
+  return 0;
 }
 
 } // namespace doc

third_party/CMakeLists.txt

@@ -112,6 +112,9 @@ endif()
 add_library(tinyexpr tinyexpr/tinyexpr.c)
 target_include_directories(tinyexpr PUBLIC tinyexpr)
 
+# cityhash
+add_subdirectory(cityhash)
+
 # lua
 if(ENABLE_SCRIPTING)
   add_library(lua

third_party/cityhash

@@ -0,0 +1 @@
+Subproject commit 757152d474e395adfcd1440d275b5dd0d1997f49