Add xxhash

third_party/xxhash/cmake_unofficial/README.md

@@ -0,0 +1,37 @@
+
+## Usage
+
+### Way 1: import targets
+Build xxHash targets:
+
+    cd </path/to/xxHash/>
+    mkdir build
+    cd build
+    cmake ../cmake_unofficial [options]
+    cmake --build .
+    cmake --build . --target install #optional
+
+Where possible options are:
+- `-DXXHASH_BUILD_ENABLE_INLINE_API=<ON|OFF>`: adds xxhash.c for the `-DXXH_INLINE_ALL` api. ON by default.
+- `-DXXHASH_BUILD_XXHSUM=<ON|OFF>`: build the command line binary. ON by default
+- `-DBUILD_SHARED_LIBS=<ON|OFF>`: build dynamic library. ON by default.
+- `-DCMAKE_INSTALL_PREFIX=<path>`: use custom install prefix path.
+- `-DDISPATCH=<ON|OFF>`: enable dispatch mode. OFF by default.
+
+Add lines into downstream CMakeLists.txt:
+
+    find_package(xxHash 0.7 CONFIG REQUIRED)
+    ...
+    target_link_libraries(MyTarget PRIVATE xxHash::xxhash)
+
+### Way 2: Add subdirectory
+Add lines into downstream CMakeLists.txt:
+
+    option(BUILD_SHARED_LIBS "Build shared libs" OFF) #optional
+    ...
+    set(XXHASH_BUILD_ENABLE_INLINE_API OFF) #optional
+    set(XXHASH_BUILD_XXHSUM OFF) #optional
+    add_subdirectory(</path/to/xxHash/cmake_unofficial/> </path/to/xxHash/build/> EXCLUDE_FROM_ALL)
+    ...
+    target_link_libraries(MyTarget PRIVATE xxHash::xxhash)
+