/usr/share/cmake-2.8/Modules/TestBigEndian.cmake is in cmake-data 2.8.12.2-0ubuntu3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 | # - Define macro to determine endian type
# Check if the system is big endian or little endian
#  TEST_BIG_ENDIAN(VARIABLE)
#  VARIABLE - variable to store the result to
#
#=============================================================================
# Copyright 2002-2009 Kitware, Inc.
#
# Distributed under the OSI-approved BSD License (the "License");
# see accompanying file Copyright.txt for details.
#
# This software is distributed WITHOUT ANY WARRANTY; without even the
# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
# See the License for more information.
#=============================================================================
# (To distribute this file outside of CMake, substitute the full
#  License text for the above reference.)
macro(TEST_BIG_ENDIAN VARIABLE)
  if("HAVE_${VARIABLE}" MATCHES "^HAVE_${VARIABLE}$")
    message(STATUS "Check if the system is big endian")
    message(STATUS "Searching 16 bit integer")
    include(CheckTypeSize)
    CHECK_TYPE_SIZE("unsigned short" CMAKE_SIZEOF_UNSIGNED_SHORT)
    if(CMAKE_SIZEOF_UNSIGNED_SHORT EQUAL 2)
      message(STATUS "Using unsigned short")
      set(CMAKE_16BIT_TYPE "unsigned short")
    else()
      CHECK_TYPE_SIZE("unsigned int"   CMAKE_SIZEOF_UNSIGNED_INT)
      if(CMAKE_SIZEOF_UNSIGNED_INT)
        message(STATUS "Using unsigned int")
        set(CMAKE_16BIT_TYPE "unsigned int")
      else()
        CHECK_TYPE_SIZE("unsigned long"  CMAKE_SIZEOF_UNSIGNED_LONG)
        if(CMAKE_SIZEOF_UNSIGNED_LONG)
          message(STATUS "Using unsigned long")
          set(CMAKE_16BIT_TYPE "unsigned long")
        else()
          message(FATAL_ERROR "no suitable type found")
        endif()
      endif()
    endif()
    configure_file("${CMAKE_ROOT}/Modules/TestEndianess.c.in"
                   "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/TestEndianess.c"
                    IMMEDIATE @ONLY)
     file(READ "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/TestEndianess.c"
          TEST_ENDIANESS_FILE_CONTENT)
     try_compile(HAVE_${VARIABLE}
      "${CMAKE_BINARY_DIR}"
      "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/TestEndianess.c"
      OUTPUT_VARIABLE OUTPUT
      COPY_FILE "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/TestEndianess.bin" )
      if(HAVE_${VARIABLE})
        file(STRINGS "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/TestEndianess.bin"
            CMAKE_TEST_ENDIANESS_STRINGS_LE LIMIT_COUNT 1 REGEX "THIS IS LITTLE ENDIAN")
        file(STRINGS "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/TestEndianess.bin"
            CMAKE_TEST_ENDIANESS_STRINGS_BE LIMIT_COUNT 1 REGEX "THIS IS BIG ENDIAN")
        # on mac, if there are universal binaries built both will be true
        # return the result depending on the machine on which cmake runs
        if(CMAKE_TEST_ENDIANESS_STRINGS_BE  AND  CMAKE_TEST_ENDIANESS_STRINGS_LE)
          if(CMAKE_SYSTEM_PROCESSOR MATCHES powerpc)
            set(CMAKE_TEST_ENDIANESS_STRINGS_BE TRUE)
            set(CMAKE_TEST_ENDIANESS_STRINGS_LE FALSE)
          else()
            set(CMAKE_TEST_ENDIANESS_STRINGS_BE FALSE)
            set(CMAKE_TEST_ENDIANESS_STRINGS_LE TRUE)
          endif()
          message(STATUS "TEST_BIG_ENDIAN found different results, consider setting CMAKE_OSX_ARCHITECTURES or CMAKE_TRY_COMPILE_OSX_ARCHITECTURES to one or no architecture !")
        endif()
        if(CMAKE_TEST_ENDIANESS_STRINGS_LE)
          set(${VARIABLE} 0 CACHE INTERNAL "Result of TEST_BIG_ENDIAN" FORCE)
          message(STATUS "Check if the system is big endian - little endian")
        endif()
        if(CMAKE_TEST_ENDIANESS_STRINGS_BE)
          set(${VARIABLE} 1 CACHE INTERNAL "Result of TEST_BIG_ENDIAN" FORCE)
          message(STATUS "Check if the system is big endian - big endian")
        endif()
        if(NOT CMAKE_TEST_ENDIANESS_STRINGS_BE  AND  NOT CMAKE_TEST_ENDIANESS_STRINGS_LE)
          message(SEND_ERROR "TEST_BIG_ENDIAN found no result!")
        endif()
        file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log
          "Determining if the system is big endian passed with the following output:\n${OUTPUT}\nTestEndianess.c:\n${TEST_ENDIANESS_FILE_CONTENT}\n\n")
      else()
        message(STATUS "Check if the system is big endian - failed")
        file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log
          "Determining if the system is big endian failed with the following output:\n${OUTPUT}\nTestEndianess.c:\n${TEST_ENDIANESS_FILE_CONTENT}\n\n")
        set(${VARIABLE})
      endif()
  endif()
endmacro()
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