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 "mpi-internal.h"
 15
 16int mpi_add(MPI w, MPI u, MPI v)
 17{
 18	mpi_ptr_t wp, up, vp;
 19	mpi_size_t usize, vsize, wsize;
 20	int usign, vsign, wsign;
 21	int err;
 22
 23	if (u->nlimbs < v->nlimbs) { /* Swap U and V. */
 24		usize = v->nlimbs;
 25		usign = v->sign;
 26		vsize = u->nlimbs;
 27		vsign = u->sign;
 28		wsize = usize + 1;
 29		err = RESIZE_IF_NEEDED(w, wsize);
 30		if (err)
 31			return err;
 32		/* These must be after realloc (u or v may be the same as w).  */
 33		up = v->d;
 34		vp = u->d;
 35	} else {
 36		usize = u->nlimbs;
 37		usign = u->sign;
 38		vsize = v->nlimbs;
 39		vsign = v->sign;
 40		wsize = usize + 1;
 41		err = RESIZE_IF_NEEDED(w, wsize);
 42		if (err)
 43			return err;
 44		/* These must be after realloc (u or v may be the same as w).  */
 45		up = u->d;
 46		vp = v->d;
 47	}
 48	wp = w->d;
 49	wsign = 0;
 50
 51	if (!vsize) {  /* simple */
 52		MPN_COPY(wp, up, usize);
 53		wsize = usize;
 54		wsign = usign;
 55	} else if (usign != vsign) { /* different sign */
 56		/* This test is right since USIZE >= VSIZE */
 57		if (usize != vsize) {
 58			mpihelp_sub(wp, up, usize, vp, vsize);
 59			wsize = usize;
 60			MPN_NORMALIZE(wp, wsize);
 61			wsign = usign;
 62		} else if (mpihelp_cmp(up, vp, usize) < 0) {
 63			mpihelp_sub_n(wp, vp, up, usize);
 64			wsize = usize;
 65			MPN_NORMALIZE(wp, wsize);
 66			if (!usign)
 67				wsign = 1;
 68		} else {
 69			mpihelp_sub_n(wp, up, vp, usize);
 70			wsize = usize;
 71			MPN_NORMALIZE(wp, wsize);
 72			if (usign)
 73				wsign = 1;
 74		}
 75	} else { /* U and V have same sign. Add them. */
 76		mpi_limb_t cy = mpihelp_add(wp, up, usize, vp, vsize);
 77		wp[usize] = cy;
 78		wsize = usize + cy;
 79		if (usign)
 80			wsign = 1;
 81	}
 82
 83	w->nlimbs = wsize;
 84	w->sign = wsign;
 85	return 0;
 86}
 87EXPORT_SYMBOL_GPL(mpi_add);
 88
 89int mpi_sub(MPI w, MPI u, MPI v)
 90{
 91	int err;
 92	MPI vv;
 93
 94	vv = mpi_copy(v);
 95	if (!vv)
 96		return -ENOMEM;
 97
 98	vv->sign = !vv->sign;
 99	err = mpi_add(w, u, vv);
100	mpi_free(vv);
101
102	return err;
103}
104EXPORT_SYMBOL_GPL(mpi_sub);
105
106int mpi_addm(MPI w, MPI u, MPI v, MPI m)
107{
108	return mpi_add(w, u, v) ?:
109	       mpi_mod(w, w, m);
110}
111EXPORT_SYMBOL_GPL(mpi_addm);
112
113int mpi_subm(MPI w, MPI u, MPI v, MPI m)
114{
115	return mpi_sub(w, u, v) ?:
116	       mpi_mod(w, w, m);
117}
118EXPORT_SYMBOL_GPL(mpi_subm);