FAQ:

1. How to get only the code from the git repository?
Create a local directory to clone into
  mkdir my_hysop && cd  my_hysop
Initialise an empty git local repository
  git init
Configure it for sparse checkout
  git config core.sparsecheckout true
Add the remote information
  git remote add -f origin git+ssh://<USERNAME>@scm.forge.imag.fr/var/lib/gforge/chroot/scmrepos/git/hysop/hysop.git
Select the HySoP directory (that contains all the code)
  echo HySoP/ >> .git/info/sparse-checkout
Get all files (only from the HySoP directory)
  git checkout master

Remarks:
Solution comes from http://stackoverflow.com/questions/4114887/is-it-possible-to-do-a-sparse-checkout-without-checking-out-the-whole-repository
It keeps the directory/files tree as git sees all files as a single unit.
(see http://stackoverflow.com/questions/2336580/sparse-checkout-in-git-1-7-0)


2. How to use a single precision version ?
Apply the patch :
  patch -p0 < utils/ToSinglePrecision.patch
To reverse the patch:
  patch -p0 -R < utils/ToSinglePrecision.patch