Adding assert_ndk_version for Android from Jørgen Tjernø.

- Ceres now requires Android NDK version >= r9d to compile, Jørgen's
  script allows a clean way to verify this condition is met before
  trying to compile for Android.
- Note that this is a modified version of the original script, which
  adds support for versions >= 10, and fixes extraction of the version
  number now that the architecture is also included.

Change-Id: Icd7ffd25407bcf29af007e30b5da5d18eb799adf

jni/Android.mk

diff --git a/jni/Android.mk b/jni/Android.mk
index a05084c..fa89eef 100644
--- a/jni/Android.mk
+++ b/jni/Android.mk
@@ -74,6 +74,11 @@
 
 LOCAL_PATH := $(call my-dir)
 
+# Ceres requires at least NDK version r9d to compile.
+ifneq ($(shell $(LOCAL_PATH)/assert_ndk_version.sh "r9d"), true)
+  $(error Ceres requires NDK version r9d or greater)
+endif
+
 EIGEN_PATH := $(EIGEN_PATH)
 CERES_INCLUDE_PATHS := $(CERES_EXTRA_INCLUDES)
 CERES_INCLUDE_PATHS += $(LOCAL_PATH)/../internal

jni/assert_ndk_version.sh

diff --git a/jni/assert_ndk_version.sh b/jni/assert_ndk_version.sh
new file mode 100755
index 0000000..f586018
--- /dev/null
+++ b/jni/assert_ndk_version.sh
@@ -0,0 +1,110 @@
+#!/bin/bash
+
+# Bash script to assert that the current version of the NDK is at least the
+# specified version. Prints 'true' to standard out if it's the right version,
+# 'false' if it's not.
+#
+# Typically used like this, in your jni/Android.mk:
+#
+#   ifneq ($(shell $(LOCAL_PATH)/assert_ndk_version.sh "r5c"),true)
+#     $(error NDK version r5c or greater required)
+#   endif
+#
+# See https://gist.github.com/2878774 for asserting SDK version.
+#
+# Retrieved from: https://gist.github.com/jorgenpt/1961404 on 2014-06-03.
+#
+# Copyright (c) 2012, Lookout, Inc. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+# 1. Redistributions of source code must retain the above copyright notice,
+#    this list of conditions and the following disclaimer.
+#
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+# TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+# PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+# OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+# WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+# OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+# ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
+# Author: jorgenpt@gmail.com (Jorgen Tjerno)
+#         alexs.mac@gmail.com (Alex Stewart)
+
+# Extracts 'r5c' into '5 c', also handles newer versions of the form
+# 'r9d (64-bit)' and versions >= 10.
+function get_major_minor() {
+  # r9d (64-bit) -> '9d', also handle versions >= 10.
+  local version=$(echo "$1" | sed 's/r\([0-9]\{1,2\}[a-z]\).*/\1/')
+  local major=$(echo "$version" | sed 's/\([0-9]\{1,2\}\).*/\1/')
+  local minor=$(echo "$version" | sed 's/^[0-9]*//')
+  echo "$major $minor"
+}
+
+if [[ -z "$1" ]]; then
+  echo "Usage: $0 <required version>" >&2
+  echo " For example: $0 r5c" >&2
+  exit 1
+fi
+
+# Assert that the expected version is at least 4.
+declare -a expected_version
+expected_version=( $(get_major_minor "$1") )
+if [[ ${expected_version[0]} -le 4 ]]; then
+  echo "Cannot test for versions less than r5: r4 doesn't have a version file." >&2
+  echo false
+  exit 1
+fi
+
+if [[ ! -d "$ANDROID_NDK_ROOT" ]]; then
+  # Attempt to find ndk-build on the path.
+  ANDROID_NDK_ROOT=$(dirname $(which ndk-build))
+  if [ ! -s "$ANDROID_NDK_ROOT" ]; then
+    echo "Failed to find either ANDROID_NDK_ROOT or ndk-build."
+    echo false
+    exit 1
+  fi
+fi
+
+release_file="$ANDROID_NDK_ROOT/RELEASE.TXT"
+
+# NDK version r4 or earlier doesn't have a RELEASE.txt, and we just asserted
+# that the person was looking for r5 or above, so that implies that this is an
+# invalid version.
+if [ ! -s "$release_file" ]; then
+  echo false
+  exit 0
+fi
+
+# Make sure the data is at least kinda sane.
+version=$(grep '^r' $release_file)
+declare -a actual_version
+actual_version=( $(get_major_minor "$version") )
+if [ -z "$version" ] || [ -z "${actual_version[0]}" ]; then
+  echo "Invalid RELEASE.txt: $(cat $release_file)" >&2
+  echo false
+  exit 1
+fi
+
+if [[ ${actual_version[0]} -lt ${expected_version[0]} ]]; then
+  echo "false"
+elif [[ ${actual_version[0]} -eq ${expected_version[0]} ]]; then
+  # This uses < and not -lt because they're string identifiers (a, b, c, etc)
+  if [[ "${actual_version[1]}" < "${expected_version[1]}" ]]; then
+    echo "false"
+  else
+    echo "true"
+  fi
+else
+  echo "true"
+fi