text: #!/bin/sh
  #
  # Detects OS we're compiling on and outputs a file specified by the first
  # argument, which in turn gets read while processing Makefile.
  #
  # The output will set the following variables:
  #   CC                          C Compiler path
  #   CXX                         C++ Compiler path
  #   PLATFORM_LDFLAGS            Linker flags
  #   PLATFORM_LIBS               Libraries flags
  #   PLATFORM_SHARED_EXT         Extension for shared libraries
  #   PLATFORM_SHARED_LDFLAGS     Flags for building shared library
  #                               This flag is embedded just before the name
  #                               of the shared library without intervening spaces
  #   PLATFORM_SHARED_CFLAGS      Flags for compiling objects for shared library
  #   PLATFORM_CCFLAGS            C compiler flags
  #   PLATFORM_CXXFLAGS           C++ compiler flags.  Will contain:
  #   PLATFORM_SHARED_VERSIONED   Set to 'true' if platform supports versioned
  #                               shared libraries, empty otherwise.
  #
  # The PLATFORM_CCFLAGS and PLATFORM_CXXFLAGS might include the following:
  #
  #       -DLEVELDB_ATOMIC_PRESENT     if <atomic> is present
  #       -DLEVELDB_PLATFORM_POSIX     for Posix-based platforms
  #       -DSNAPPY                     if the Snappy library is present
  #
  
  OUTPUT=$1
  PREFIX=$2
  if test -z "$OUTPUT" || test -z "$PREFIX"; then
    echo "usage: $0 <output-filename> <directory_prefix>" >&2
    exit 1
  fi
  
  # Delete existing output, if it exists
  rm -f $OUTPUT
  touch $OUTPUT
  
  if test -z "$CC"; then
      CC=cc
  fi
  
  if test -z "$CXX"; then
      CXX=g++
  fi
  
  if test -z "$TMPDIR"; then
      TMPDIR=/tmp
  fi
  
  # Detect OS
  if test -z "$TARGET_OS"; then
      TARGET_OS=`uname -s`
  fi
  
  COMMON_FLAGS=
  CROSS_COMPILE=
  PLATFORM_CCFLAGS=
  PLATFORM_CXXFLAGS=
  PLATFORM_LDFLAGS=
  PLATFORM_LIBS=
  PLATFORM_SHARED_EXT="so"
  PLATFORM_SHARED_LDFLAGS="-shared -Wl,-soname -Wl,"
  PLATFORM_SHARED_CFLAGS="-fPIC"
  PLATFORM_SHARED_VERSIONED=true
  
  MEMCMP_FLAG=
  if [ "$CXX" = "g++" ]; then
      # Use libc's memcmp instead of GCC's memcmp.  This results in ~40%
      # performance improvement on readrandom under gcc 4.4.3 on Linux/x86.
      MEMCMP_FLAG="-fno-builtin-memcmp"
  fi
  
  case "$TARGET_OS" in
      CYGWIN_*)
          PLATFORM=OS_LINUX
          COMMON_FLAGS="$MEMCMP_FLAG -lpthread -DOS_LINUX -DCYGWIN"
          PLATFORM_LDFLAGS="-lpthread"
          PORT_FILE=port/port_posix.cc
          ;;
      Darwin)
          PLATFORM=OS_MACOSX
          COMMON_FLAGS="$MEMCMP_FLAG -DOS_MACOSX"
          PLATFORM_SHARED_EXT=dylib
          [ -z "$INSTALL_PATH" ] && INSTALL_PATH=`pwd`
          PLATFORM_SHARED_LDFLAGS="-dynamiclib -install_name $INSTALL_PATH/"
          PORT_FILE=port/port_posix.cc
          ;;
      Linux)
          PLATFORM=OS_LINUX
          COMMON_FLAGS="$MEMCMP_FLAG -pthread -DOS_LINUX"
          PLATFORM_LDFLAGS="-pthread"
          PORT_FILE=port/port_posix.cc
          ;;
      SunOS)
          PLATFORM=OS_SOLARIS
          COMMON_FLAGS="$MEMCMP_FLAG -D_REENTRANT -DOS_SOLARIS"
          PLATFORM_LIBS="-lpthread -lrt"
          PORT_FILE=port/port_posix.cc
          ;;
      FreeBSD)
          PLATFORM=OS_FREEBSD
          COMMON_FLAGS="$MEMCMP_FLAG -D_REENTRANT -DOS_FREEBSD"
          PLATFORM_LIBS="-lpthread"
          PORT_FILE=port/port_posix.cc
          ;;
      GNU/kFreeBSD)
          PLATFORM=OS_KFREEBSD
          COMMON_FLAGS="$MEMCMP_FLAG -D_REENTRANT -DOS_KFREEBSD"
          PLATFORM_LIBS="-lpthread"
          PORT_FILE=port/port_posix.cc
          ;;
      NetBSD)
          PLATFORM=OS_NETBSD
          COMMON_FLAGS="$MEMCMP_FLAG -D_REENTRANT -DOS_NETBSD"
          PLATFORM_LIBS="-lpthread -lgcc_s"
          PORT_FILE=port/port_posix.cc
          ;;
      OpenBSD)
          PLATFORM=OS_OPENBSD
          COMMON_FLAGS="$MEMCMP_FLAG -D_REENTRANT -DOS_OPENBSD"
          PLATFORM_LDFLAGS="-pthread"
          PORT_FILE=port/port_posix.cc
          ;;
      DragonFly)
          PLATFORM=OS_DRAGONFLYBSD
          COMMON_FLAGS="$MEMCMP_FLAG -D_REENTRANT -DOS_DRAGONFLYBSD"
          PLATFORM_LIBS="-lpthread"
          PORT_FILE=port/port_posix.cc
          ;;
      OS_ANDROID_CROSSCOMPILE)
          PLATFORM=OS_ANDROID
          COMMON_FLAGS="$MEMCMP_FLAG -D_REENTRANT -DOS_ANDROID -DLEVELDB_PLATFORM_POSIX"
          PLATFORM_LDFLAGS=""  # All pthread features are in the Android C library
          PORT_FILE=port/port_posix.cc
          CROSS_COMPILE=true
          ;;
      HP-UX)
          PLATFORM=OS_HPUX
          COMMON_FLAGS="$MEMCMP_FLAG -D_REENTRANT -DOS_HPUX"
          PLATFORM_LDFLAGS="-pthread"
          PORT_FILE=port/port_posix.cc
          # man ld: +h internal_name
          PLATFORM_SHARED_LDFLAGS="-shared -Wl,+h -Wl,"
          ;;
      IOS)
          PLATFORM=IOS
          COMMON_FLAGS="$MEMCMP_FLAG -DOS_MACOSX"
          [ -z "$INSTALL_PATH" ] && INSTALL_PATH=`pwd`
          PORT_FILE=port/port_posix.cc
          PLATFORM_SHARED_EXT=
          PLATFORM_SHARED_LDFLAGS=
          PLATFORM_SHARED_CFLAGS=
          PLATFORM_SHARED_VERSIONED=
          ;;
      OS_WINDOWS_CROSSCOMPILE | NATIVE_WINDOWS)
          PLATFORM=OS_WINDOWS
          COMMON_FLAGS="-fno-builtin-memcmp -D_REENTRANT -DOS_WINDOWS -DLEVELDB_PLATFORM_WINDOWS -DWINVER=0x0500 -D__USE_MINGW_ANSI_STDIO=1"
          PLATFORM_SOURCES="util/env_win.cc"
          PLATFORM_LIBS="-lshlwapi"
          PORT_FILE=port/port_win.cc
          CROSS_COMPILE=true
          ;;
      *)
          echo "Unknown platform!" >&2
          exit 1
  esac
  
  # We want to make a list of all cc files within util, db, table, and helpers
  # except for the test and benchmark files. By default, find will output a list
  # of all files matching either rule, so we need to append -print to make the
  # prune take effect.
  DIRS="$PREFIX/db $PREFIX/util $PREFIX/table"
  
  set -f # temporarily disable globbing so that our patterns aren't expanded
  PRUNE_TEST="-name *test*.cc -prune"
  PRUNE_BENCH="-name *_bench.cc -prune"
  PRUNE_TOOL="-name leveldb_main.cc -prune"
  PORTABLE_FILES=`find $DIRS $PRUNE_TEST -o $PRUNE_BENCH -o $PRUNE_TOOL -o -name '*.cc' -print | sort | sed "s,^$PREFIX/,," | tr "\n" " "`
  
  set +f # re-enable globbing
  
  # The sources consist of the portable files, plus the platform-specific port
  # file.
  echo "SOURCES=$PORTABLE_FILES $PORT_FILE" >> $OUTPUT
  echo "MEMENV_SOURCES=helpers/memenv/memenv.cc" >> $OUTPUT
  
  if [ "$CROSS_COMPILE" = "true" ]; then
      # Cross-compiling; do not try any compilation tests.
      true
  else
      CXXOUTPUT="${TMPDIR}/leveldb_build_detect_platform-cxx.$$"
  
      # If -std=c++0x works, use <atomic> as fallback for when memory barriers
      # are not available.
      $CXX $CXXFLAGS -std=c++0x -x c++ - -o $CXXOUTPUT 2>/dev/null  <<EOF
        #include <atomic>
        int main() {}
  EOF
      if [ "$?" = 0 ]; then
          COMMON_FLAGS="$COMMON_FLAGS -DLEVELDB_PLATFORM_POSIX -DLEVELDB_ATOMIC_PRESENT"
          PLATFORM_CXXFLAGS="-std=c++0x"
      else
          COMMON_FLAGS="$COMMON_FLAGS -DLEVELDB_PLATFORM_POSIX"
      fi
  
      # Test whether tcmalloc is available
      $CXX $CXXFLAGS -x c++ - -o $CXXOUTPUT -ltcmalloc 2>/dev/null  <<EOF
        int main() {}
  EOF
      if [ "$?" = 0 ]; then
          PLATFORM_LIBS="$PLATFORM_LIBS -ltcmalloc"
      fi
  
      rm -f $CXXOUTPUT 2>/dev/null
  fi
  
  PLATFORM_CCFLAGS="$PLATFORM_CCFLAGS $COMMON_FLAGS"
  PLATFORM_CXXFLAGS="$PLATFORM_CXXFLAGS $COMMON_FLAGS"
  
  echo "CC=$CC" >> $OUTPUT
  echo "CXX=$CXX" >> $OUTPUT
  echo "PLATFORM=$PLATFORM" >> $OUTPUT
  echo "PLATFORM_LDFLAGS=$PLATFORM_LDFLAGS" >> $OUTPUT
  echo "PLATFORM_LIBS=$PLATFORM_LIBS" >> $OUTPUT
  echo "PLATFORM_CCFLAGS=$PLATFORM_CCFLAGS" >> $OUTPUT
  echo "PLATFORM_CXXFLAGS=$PLATFORM_CXXFLAGS" >> $OUTPUT
  echo "PLATFORM_SHARED_CFLAGS=$PLATFORM_SHARED_CFLAGS" >> $OUTPUT
  echo "PLATFORM_SHARED_EXT=$PLATFORM_SHARED_EXT" >> $OUTPUT
  echo "PLATFORM_SHARED_LDFLAGS=$PLATFORM_SHARED_LDFLAGS" >> $OUTPUT
  echo "PLATFORM_SHARED_VERSIONED=$PLATFORM_SHARED_VERSIONED" >> $OUTPUT
  