Re: [PATCH 2/3] lib/mpi: Add mpi_sub_ui()

[Ard Biesheuvel <ardb@kernel.org>]

On Fri, 10 Jul 2020 at 13:16, Stephan Müller <smueller@chronox.de> wrote:
>
> Add mpi_sub_ui() based on Gnu PG mpz_sub_ui() from mpz/aors_ui.h
> adapting the code to the kernel's structures and coding style and also
> removing the defines used to produce mpz_sub_ui() and mpz_add_ui()
> from the same code.
>

Isn't GnuPG GPLv3 ?


> Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
> Signed-off-by: Stephan Mueller <smueller@chronox.de>
> ---
>  include/linux/mpi.h  |  3 +++
>  lib/mpi/Makefile     |  1 +
>  lib/mpi/mpi-sub-ui.c | 60 ++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 64 insertions(+)
>  create mode 100644 lib/mpi/mpi-sub-ui.c
>
> diff --git a/include/linux/mpi.h b/include/linux/mpi.h
> index 7bd6d8af0004..5d906dfbf3ed 100644
> --- a/include/linux/mpi.h
> +++ b/include/linux/mpi.h
> @@ -63,6 +63,9 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod);
>  int mpi_cmp_ui(MPI u, ulong v);
>  int mpi_cmp(MPI u, MPI v);
>
> +/*-- mpi-sub-ui.c --*/
> +int mpi_sub_ui(MPI w, MPI u, unsigned long vval);
> +
>  /*-- mpi-bit.c --*/
>  void mpi_normalize(MPI a);
>  unsigned mpi_get_nbits(MPI a);
> diff --git a/lib/mpi/Makefile b/lib/mpi/Makefile
> index d5874a7f5ff9..43b8fce14079 100644
> --- a/lib/mpi/Makefile
> +++ b/lib/mpi/Makefile
> @@ -16,6 +16,7 @@ mpi-y = \
>         mpicoder.o                      \
>         mpi-bit.o                       \
>         mpi-cmp.o                       \
> +       mpi-sub-ui.o                    \
>         mpih-cmp.o                      \
>         mpih-div.o                      \
>         mpih-mul.o                      \
> diff --git a/lib/mpi/mpi-sub-ui.c b/lib/mpi/mpi-sub-ui.c
> new file mode 100644
> index 000000000000..fa6b085bac36
> --- /dev/null
> +++ b/lib/mpi/mpi-sub-ui.c
> @@ -0,0 +1,60 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/* mpi-sub-ui.c  -  MPI functions
> + *      Copyright 1991, 1993, 1994, 1996, 1999-2002, 2004, 2012, 2013, 2015
> + *      Free Software Foundation, Inc.
> + *
> + * This file is part of GnuPG.
> + *
> + * Note: This code is heavily based on the GNU MP Library.
> + *      Actually it's the same code with only minor changes in the
> + *      way the data is stored; this is to support the abstraction
> + *      of an optional secure memory allocation which may be used
> + *      to avoid revealing of sensitive data due to paging etc.
> + *      The GNU MP Library itself is published under the LGPL;
> + *      however I decided to publish this code under the plain GPL.
> + */
> +
> +#include "mpi-internal.h"
> +
> +int mpi_sub_ui(MPI w, MPI u, unsigned long vval)
> +{
> +       if (u->nlimbs == 0) {
> +               if (mpi_resize(w, 1) < 0)
> +                       return -ENOMEM;
> +               w->d[0] = vval;
> +               w->nlimbs = (vval != 0);
> +               w->sign = (vval != 0);
> +               return 0;
> +       }
> +
> +       /* If not space for W (and possible carry), increase space. */
> +       if (mpi_resize(w, u->nlimbs + 1))
> +               return -ENOMEM;
> +
> +       if (u->sign) {
> +               mpi_limb_t cy;
> +
> +               cy = mpihelp_add_1(w->d, u->d, u->nlimbs, (mpi_limb_t) vval);
> +               w->d[u->nlimbs] = cy;
> +               w->nlimbs = u->nlimbs + cy;
> +               w->sign = 1;
> +       } else {
> +               /* The signs are different.  Need exact comparison to determine
> +                * which operand to subtract from which.
> +                */
> +               if (u->nlimbs == 1 && u->d[0] < vval) {
> +                       w->d[0] = vval - u->d[0];
> +                       w->nlimbs = 1;
> +                       w->sign = 1;
> +               } else {
> +                       mpihelp_sub_1(w->d, u->d, u->nlimbs, (mpi_limb_t) vval);
> +                       /* Size can decrease with at most one limb. */
> +                       w->nlimbs = (u->nlimbs - (w->d[u->nlimbs - 1] == 0));
> +                       w->sign = 0;
> +               }
> +       }
> +
> +       mpi_normalize(w);
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(mpi_sub_ui);
> --
> 2.26.2
>
>
>
>