if (WIN32)
  # mingw compiler is known to produce unstable SSE code with -O3 hence we are trying to use -O2 instead
  if(CMAKE_COMPILER_IS_GNUCXX)
    foreach(flags CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_RELEASE CMAKE_CXX_FLAGS_DEBUG)
      string(REPLACE "-O3" "-O2" ${flags} "${${flags}}")
    endforeach()
  endif()

  if(CMAKE_COMPILER_IS_GNUCC)
    foreach(flags CMAKE_C_FLAGS CMAKE_C_FLAGS_RELEASE CMAKE_C_FLAGS_DEBUG)
      string(REPLACE "-O3" "-O2" ${flags} "${${flags}}")
    endforeach()
  endif()
endif()

if(MSVC)
  if(CMAKE_CXX_FLAGS STREQUAL CMAKE_CXX_FLAGS_INIT)
    # override cmake default exception handling option
    string(REPLACE "/EHsc" "/EHa" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}"  CACHE STRING "Flags used by the compiler during all build types." FORCE)
  endif()
endif()

set(OPENCV_EXTRA_C_FLAGS "")
set(OPENCV_EXTRA_C_FLAGS_RELEASE "")
set(OPENCV_EXTRA_C_FLAGS_DEBUG "")
set(OPENCV_EXTRA_EXE_LINKER_FLAGS "")
set(OPENCV_EXTRA_EXE_LINKER_FLAGS_RELEASE "")
set(OPENCV_EXTRA_EXE_LINKER_FLAGS_DEBUG "")

if(CMAKE_COMPILER_IS_GNUCXX)
  # High level of warnings.
  set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -Wall")

  # The -Wno-long-long is required in 64bit systems when including sytem headers.
  if(X86_64)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -Wno-long-long")
  endif()

  # We need pthread's
  if(UNIX AND NOT ANDROID)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -pthread")
  endif()

  if(OPENCV_WARNINGS_ARE_ERRORS)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -Werror")
  endif()

  if(X86 AND NOT MINGW64 AND NOT X86_64 AND NOT APPLE)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -march=i686")
  endif()

  # Other optimizations
  if(ENABLE_OMIT_FRAME_POINTER)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -fomit-frame-pointer")
  else()
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -fno-omit-frame-pointer")
  endif()
  if(ENABLE_FAST_MATH)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -ffast-math")
  endif()
  if(ENABLE_POWERPC)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -mcpu=G3 -mtune=G5")
  endif()
  if(ENABLE_SSE)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -msse")
  endif()
  if(ENABLE_SSE2)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -msse2")
  endif()

  # SSE3 and further should be disabled under MingW because it generates compiler errors
  if(NOT MINGW)
    if(ENABLE_SSE3)
      set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -msse3")
    endif()

    if(${CMAKE_OPENCV_GCC_VERSION_NUM} GREATER 402)
      set(HAVE_GCC43_OR_NEWER 1)
    endif()
    if(${CMAKE_OPENCV_GCC_VERSION_NUM} GREATER 401)
      set(HAVE_GCC42_OR_NEWER 1)
    endif()

    if(HAVE_GCC42_OR_NEWER OR APPLE)
      if(ENABLE_SSSE3)
        set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -mssse3")
      endif()
      if(HAVE_GCC43_OR_NEWER)
        if(ENABLE_SSE41)
           set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -msse4.1")
        endif()
        if(ENABLE_SSE42)
           set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -msse4.2")
        endif()
      endif()
    endif()
  endif(NOT MINGW)

  if(X86 OR X86_64)
    if(NOT APPLE AND CMAKE_SIZEOF_VOID_P EQUAL 4)
       if(ENABLE_SSE2)
         set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -mfpmath=sse")# !! important - be on the same wave with x64 compilers
       else()
         set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -mfpmath=387")
       endif()
    endif()
  endif()

  # Profiling?
  if(ENABLE_PROFILING)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -pg -g")
    # turn off incompatible options
    foreach(flags CMAKE_CXX_FLAGS CMAKE_C_FLAGS CMAKE_CXX_FLAGS_RELEASE CMAKE_C_FLAGS_RELEASE CMAKE_CXX_FLAGS_DEBUG CMAKE_C_FLAGS_DEBUG OPENCV_EXTRA_C_FLAGS_RELEASE)
      string(REPLACE "-fomit-frame-pointer" "" ${flags} "${${flags}}")
      string(REPLACE "-ffunction-sections" "" ${flags} "${${flags}}")
    endforeach()
  elseif(NOT APPLE AND NOT ANDROID)
    # Remove unreferenced functions: function level linking
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -ffunction-sections")
  endif()

  set(OPENCV_EXTRA_C_FLAGS_RELEASE "${OPENCV_EXTRA_C_FLAGS_RELEASE} -DNDEBUG")
  set(OPENCV_EXTRA_C_FLAGS_DEBUG "${OPENCV_EXTRA_C_FLAGS_DEBUG} -O0 -DDEBUG -D_DEBUG")
  if(BUILD_WITH_DEBUG_INFO)
    set(OPENCV_EXTRA_C_FLAGS_DEBUG "${OPENCV_EXTRA_C_FLAGS_DEBUG} -ggdb3")
  endif()
endif()

if(MSVC)
  set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} /D _CRT_SECURE_NO_DEPRECATE /D _CRT_NONSTDC_NO_DEPRECATE /D _SCL_SECURE_NO_WARNINGS")
  # 64-bit portability warnings, in MSVC80
  if(MSVC80)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} /Wp64")
  endif()

  if(BUILD_WITH_DEBUG_INFO)
    set(OPENCV_EXTRA_EXE_LINKER_FLAGS_RELEASE "${OPENCV_EXTRA_EXE_LINKER_FLAGS_RELEASE} /debug")
  endif()

  # Remove unreferenced functions: function level linking
  set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} /Gy")
  if(NOT MSVC_VERSION LESS 1400)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} /bigobj")
  endif()
  if(BUILD_WITH_DEBUG_INFO)
    set(OPENCV_EXTRA_C_FLAGS_RELEASE "${OPENCV_EXTRA_C_FLAGS_RELEASE} /Zi")
  endif()

  if(NOT MSVC64)
    # 64-bit MSVC compiler uses SSE/SSE2 by default
    if(ENABLE_SSE)
      set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} /arch:SSE")
    endif()
    if(ENABLE_SSE2)
      set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} /arch:SSE2")
    endif()
  endif()
  
  if(ENABLE_SSE3)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} /arch:SSE3")
  endif()
  if(ENABLE_SSE4_1)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} /arch:SSE4.1")
  endif()
  
  if(ENABLE_SSE OR ENABLE_SSE2 OR ENABLE_SSE3 OR ENABLE_SSE4_1)
    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} /Oi")
  endif()
  
  if(X86 OR X86_64)
    if(CMAKE_SIZEOF_VOID_P EQUAL 4 AND ENABLE_SSE2)
      set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} /fp:fast")# !! important - be on the same wave with x64 compilers
    endif()
  endif()
endif()

# Extra link libs if the user selects building static libs:
if(NOT BUILD_SHARED_LIBS AND CMAKE_COMPILER_IS_GNUCXX AND NOT ANDROID)
  # Android does not need these settings because they are already set by toolchain file
  set(OPENCV_LINKER_LIBS ${OPENCV_LINKER_LIBS} stdc++)
  set(OPENCV_EXTRA_C_FLAGS "-fPIC ${OPENCV_EXTRA_C_FLAGS}")
endif()

# Add user supplied extra options (optimization, etc...)
# ==========================================================
set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS}" CACHE INTERNAL "Extra compiler options")
set(OPENCV_EXTRA_C_FLAGS_RELEASE "${OPENCV_EXTRA_C_FLAGS_RELEASE}" CACHE INTERNAL "Extra compiler options for Release build")
set(OPENCV_EXTRA_C_FLAGS_DEBUG "${OPENCV_EXTRA_C_FLAGS_DEBUG}" CACHE INTERNAL "Extra compiler options for Debug build")
set(OPENCV_EXTRA_EXE_LINKER_FLAGS "${OPENCV_EXTRA_EXE_LINKER_FLAGS}" CACHE INTERNAL "Extra linker flags")
set(OPENCV_EXTRA_EXE_LINKER_FLAGS_RELEASE "${OPENCV_EXTRA_EXE_LINKER_FLAGS_RELEASE}" CACHE INTERNAL "Extra linker flags for Release build")
set(OPENCV_EXTRA_EXE_LINKER_FLAGS_DEBUG "${OPENCV_EXTRA_EXE_LINKER_FLAGS_DEBUG}" CACHE INTERNAL "Extra linker flags for Debug build")

#combine all "extra" options
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OPENCV_EXTRA_C_FLAGS}")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OPENCV_EXTRA_C_FLAGS}")
set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}  ${OPENCV_EXTRA_C_FLAGS_RELEASE}")
set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} ${OPENCV_EXTRA_C_FLAGS_RELEASE}")
set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} ${OPENCV_EXTRA_C_FLAGS_DEBUG}")
set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} ${OPENCV_EXTRA_C_FLAGS_DEBUG}")
set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${OPENCV_EXTRA_EXE_LINKER_FLAGS}")
set(CMAKE_EXE_LINKER_FLAGS_RELEASE "${CMAKE_EXE_LINKER_FLAGS_RELEASE} ${OPENCV_EXTRA_EXE_LINKER_FLAGS_RELEASE}")
set(CMAKE_EXE_LINKER_FLAGS_DEBUG "${CMAKE_EXE_LINKER_FLAGS_DEBUG} ${OPENCV_EXTRA_EXE_LINKER_FLAGS_DEBUG}")

if(MSVC)
  # avoid warnings from MSVC about overriding the /W* option
  # we replace /W3 with /W4 only for C++ files,
  # since all the 3rd-party libraries OpenCV uses are in C,
  # and we do not care about their warnings.
  string(REPLACE "/W3" "/W4" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
  string(REPLACE "/W3" "/W4" CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}")
  string(REPLACE "/W3" "/W4" CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG}")
  
  # allow extern "C" functions throw exceptions
  foreach(flags CMAKE_C_FLAGS CMAKE_C_FLAGS_RELEASE CMAKE_C_FLAGS_RELEASE CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_RELEASE CMAKE_CXX_FLAGS_DEBUG)
    string(REPLACE "/EHsc-" "/EHs" ${flags} "${${flags}}")
    string(REPLACE "/EHsc" "/EHs" ${flags} "${${flags}}")
    
    string(REPLACE "/Zm1000" "" ${flags} "${${flags}}")
  endforeach()

  if(NOT ENABLE_NOISY_WARNINGS)
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /wd4251") #class 'std::XXX' needs to have dll-interface to be used by clients of YYY
  endif()
endif()