mpi-add.c

  1/* mpi-add.c  -  MPI functions
  2 * Copyright (C) 1994, 1996, 1998, 2001, 2002,
  3 *               2003 Free Software Foundation, Inc.
  4 *
  5 * This file is part of Libgcrypt.
  6 *
  7 * Note: This code is heavily based on the GNU MP Library.
  8 *	 Actually it's the same code with only minor changes in the
  9 *	 way the data is stored; this is to support the abstraction
 10 *	 of an optional secure memory allocation which may be used
 11 *	 to avoid revealing of sensitive data due to paging etc.
 12 */
 13
 14#include <linux/export.h>
 15
 16#include "mpi-internal.h"
 17
 18int mpi_add(MPI w, MPI u, MPI v)
 19{
 20	mpi_ptr_t wp, up, vp;
 21	mpi_size_t usize, vsize, wsize;
 22	int usign, vsign, wsign;
 23	int err;
 24
 25	if (u->nlimbs < v->nlimbs) { /* Swap U and V. */
 26		usize = v->nlimbs;
 27		usign = v->sign;
 28		vsize = u->nlimbs;
 29		vsign = u->sign;
 30		wsize = usize + 1;
 31		err = RESIZE_IF_NEEDED(w, wsize);
 32		if (err)
 33			return err;
 34		/* These must be after realloc (u or v may be the same as w).  */
 35		up = v->d;
 36		vp = u->d;
 37	} else {
 38		usize = u->nlimbs;
 39		usign = u->sign;
 40		vsize = v->nlimbs;
 41		vsign = v->sign;
 42		wsize = usize + 1;
 43		err = RESIZE_IF_NEEDED(w, wsize);
 44		if (err)
 45			return err;
 46		/* These must be after realloc (u or v may be the same as w).  */
 47		up = u->d;
 48		vp = v->d;
 49	}
 50	wp = w->d;
 51	wsign = 0;
 52
 53	if (!vsize) {  /* simple */
 54		MPN_COPY(wp, up, usize);
 55		wsize = usize;
 56		wsign = usign;
 57	} else if (usign != vsign) { /* different sign */
 58		/* This test is right since USIZE >= VSIZE */
 59		if (usize != vsize) {
 60			mpihelp_sub(wp, up, usize, vp, vsize);
 61			wsize = usize;
 62			MPN_NORMALIZE(wp, wsize);
 63			wsign = usign;
 64		} else if (mpihelp_cmp(up, vp, usize) < 0) {
 65			mpihelp_sub_n(wp, vp, up, usize);
 66			wsize = usize;
 67			MPN_NORMALIZE(wp, wsize);
 68			if (!usign)
 69				wsign = 1;
 70		} else {
 71			mpihelp_sub_n(wp, up, vp, usize);
 72			wsize = usize;
 73			MPN_NORMALIZE(wp, wsize);
 74			if (usign)
 75				wsign = 1;
 76		}
 77	} else { /* U and V have same sign. Add them. */
 78		mpi_limb_t cy = mpihelp_add(wp, up, usize, vp, vsize);
 79		wp[usize] = cy;
 80		wsize = usize + cy;
 81		if (usign)
 82			wsign = 1;
 83	}
 84
 85	w->nlimbs = wsize;
 86	w->sign = wsign;
 87	return 0;
 88}
 89EXPORT_SYMBOL_GPL(mpi_add);
 90
 91int mpi_sub(MPI w, MPI u, MPI v)
 92{
 93	int err;
 94	MPI vv;
 95
 96	vv = mpi_copy(v);
 97	if (!vv)
 98		return -ENOMEM;
 99
100	vv->sign = !vv->sign;
101	err = mpi_add(w, u, vv);
102	mpi_free(vv);
103
104	return err;
105}
106EXPORT_SYMBOL_GPL(mpi_sub);
107
108int mpi_addm(MPI w, MPI u, MPI v, MPI m)
109{
110	return mpi_add(w, u, v) ?:
111	       mpi_mod(w, w, m);
112}
113EXPORT_SYMBOL_GPL(mpi_addm);
114
115int mpi_subm(MPI w, MPI u, MPI v, MPI m)
116{
117	return mpi_sub(w, u, v) ?:
118	       mpi_mod(w, w, m);
119}
120EXPORT_SYMBOL_GPL(mpi_subm);