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lib/mpi: Add mpi_sub_ui()

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Add mpi_sub_ui() based on Gnu MP mpz_sub_ui() function from file
mpz/aors_ui.h[1] from change id 510b83519d1c adapting the code to the
kernel's data structures, helper functions and coding style and also
removing the defines used to produce mpz_sub_ui() and mpz_add_ui()
from the same code.

[1] https://gmplib.org/repo/gmp-6.2/file/510b83519d1c/mpz/aors.h

Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Marcelo Henrique Cerri 2020-07-20 19:08:09 +02:00 committed by Herbert Xu
parent e7d2b41e5c
commit 4278e9d99e
3 changed files with 82 additions and 0 deletions
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3
include/linux/mpi.h
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@ -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);

1
lib/mpi/Makefile
View File

@ -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 \

78
lib/mpi/mpi-sub-ui.c Normal file
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@ -0,0 +1,78 @@
// SPDX-License-Identifier: GPL-2.0-or-later
/* mpi-sub-ui.c - Subtract an unsigned integer from an MPI.
*
* Copyright 1991, 1993, 1994, 1996, 1999-2002, 2004, 2012, 2013, 2015
* Free Software Foundation, Inc.
*
* This file was based on the GNU MP Library source file:
* https://gmplib.org/repo/gmp-6.2/file/510b83519d1c/mpz/aors_ui.h
*
* The GNU MP Library is free software; you can redistribute it and/or modify
* it under the terms of either:
*
* * the GNU Lesser General Public License as published by the Free
* Software Foundation; either version 3 of the License, or (at your
* option) any later version.
*
* or
*
* * the GNU General Public License as published by the Free Software
* Foundation; either version 2 of the License, or (at your option) any
* later version.
*
* or both in parallel, as here.
*
* The GNU MP Library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*
* You should have received copies of the GNU General Public License and the
* GNU Lesser General Public License along with the GNU MP Library. If not,
* see https://www.gnu.org/licenses/.
*/
#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);