Ubuntu 16.04 build for glibc >= 2.23. Or 2.14(!?)

objdump says we only need 2.14, and the cimbar binary runs on centos7...
I see this as an absolute win

package-portable-linux.sh

@@ -1,17 +1,31 @@
 #!/bin/sh
-# docker run --mount type=bind,source="$(pwd)",target="/usr/src/app" -it ubuntu:18.04
+## targeting old glibc
+# docker run --mount type=bind,source="$(pwd)",target="/usr/src/app" -it ubuntu:16.04
 
 cd /usr/src/app
+
+# https://gist.github.com/jlblancoc/99521194aba975286c80f93e47966dc5
+apt update
+apt install -y software-properties-common
+add-apt-repository -y ppa:ubuntu-toolchain-r/test
+
 apt update
-apt install -y pkgconf g++ cmake
+apt install -y pkgconf g++-7 python-pip
 apt install -y libgles2-mesa-dev libglfw3-dev
 
+# cmake (via pip)
+python -m pip install cmake
+
+# use gcc7
+update-alternatives --install /usr/bin/cc cc /usr/bin/gcc-7 100
+update-alternatives --install /usr/bin/c++ c++ /usr/bin/g++-7 100
+
 cd opencv4/
 mkdir build-portable/ && cd build-portable/
-cmake .. -DCMAKE_BUILD_TYPE=RELEASE -DBUILD_SHARED_LIBS=OFF -DOPENCV_GENERATE_PKGCONFIG=YES -DOPENCV_FORCE_3RDPARTY_BUILD=YES
+/usr/local/bin/cmake .. -DCMAKE_BUILD_TYPE=RELEASE -DBUILD_SHARED_LIBS=OFF -DOPENCV_GENERATE_PKGCONFIG=YES -DOPENCV_FORCE_3RDPARTY_BUILD=YES
 make -j5 install
 
 cd /usr/src/app
 mkdir build-portable/ && cd build-portable/
-cmake .. -DBUILD_PORTABLE_LINUX=1
+/usr/local/bin/cmake .. -DBUILD_PORTABLE_LINUX=1
 make -j5 install

src/lib/cimb_translator/test/CimbDecoderTest.cpp

@@ -56,7 +56,7 @@ TEST_CASE( "CimbDecoderTest/testPrethresholdDecode", "[unit]" )
  for (unsigned i = 0; i < 16; ++i)
  {
  cv::Mat tile = cimbar::getTile(4, i, true);
- cv::Mat tenxten(10, 10, tile.type());
+ cv::Mat tenxten(10, 10, tile.type(), cv::Scalar(0, 0, 0));
  tile.copyTo(tenxten(cv::Rect(cv::Point(1, 1), tile.size())));
 
  // grayscale and threshold, since that's what average_hash needs

src/lib/image_hash/average_hash.h

@@ -51,6 +51,10 @@ namespace image_hash
  uint64_t mval = (*hax) & 0x101010101ULL;
  const uint8_t* cv = reinterpret_cast<const uint8_t*>(&mval);
  uint8_t val = cv[0] << 4 | cv[1] << 3 | cv[2] << 2 | cv[3] << 1 | cv[4];
+ // TODO:
+ /*if (bigEndian)
+ val = cv[7] << 4 | cv[6] << 3 | cv[5] << 2 | cv[4] << 1 | cv[3];*/ // ?
+
  res |= intx::uint128(val) << bitpos;
  }
  }