CMake bug: https://cmake.org/Bug/print_bug_page.php?bug_id=13515

This function call `std::abs(double)` which should profit from better
optimizations

- cache some difference informations in order to avoid computing it several
  time
- Dichotomic search of the of pixel index

BTW, presicion hasbeen improved by doing computations on `double` instead of
`floats`.