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
 16/****************
 17 * Add the unsigned integer V to the mpi-integer U and store the
 18 * result in W. U and V may be the same.
 19 */
 20void mpi_add_ui(MPI w, MPI u, unsigned long v)
 21{
 22	mpi_ptr_t wp, up;
 23	mpi_size_t usize, wsize;
 24	int usign, wsign;
 25
 26	usize = u->nlimbs;
 27	usign = u->sign;
 28	wsign = 0;
 29
 30	/* If not space for W (and possible carry), increase space.  */
 31	wsize = usize + 1;
 32	if (w->alloced < wsize)
 33		mpi_resize(w, wsize);
 34
 35	/* These must be after realloc (U may be the same as W).  */
 36	up = u->d;
 37	wp = w->d;
 38
 39	if (!usize) {  /* simple */
 40		wp[0] = v;
 41		wsize = v ? 1:0;
 42	} else if (!usign) {  /* mpi is not negative */
 43		mpi_limb_t cy;
 44		cy = mpihelp_add_1(wp, up, usize, v);
 45		wp[usize] = cy;
 46		wsize = usize + cy;
 47	} else {
 48		/* The signs are different.  Need exact comparison to determine
 49		 * which operand to subtract from which.
 50		 */
 51		if (usize == 1 && up[0] < v) {
 52			wp[0] = v - up[0];
 53			wsize = 1;
 54		} else {
 55			mpihelp_sub_1(wp, up, usize, v);
 56			/* Size can decrease with at most one limb. */
 57			wsize = usize - (wp[usize-1] == 0);
 58			wsign = 1;
 59		}
 60	}
 61
 62	w->nlimbs = wsize;
 63	w->sign   = wsign;
 64}
 65
 66
 67void mpi_add(MPI w, MPI u, MPI v)
 68{
 69	mpi_ptr_t wp, up, vp;
 70	mpi_size_t usize, vsize, wsize;
 71	int usign, vsign, wsign;
 72
 73	if (u->nlimbs < v->nlimbs) { /* Swap U and V. */
 74		usize = v->nlimbs;
 75		usign = v->sign;
 76		vsize = u->nlimbs;
 77		vsign = u->sign;
 78		wsize = usize + 1;
 79		RESIZE_IF_NEEDED(w, wsize);
 80		/* These must be after realloc (u or v may be the same as w).  */
 81		up = v->d;
 82		vp = u->d;
 83	} else {
 84		usize = u->nlimbs;
 85		usign = u->sign;
 86		vsize = v->nlimbs;
 87		vsign = v->sign;
 88		wsize = usize + 1;
 89		RESIZE_IF_NEEDED(w, wsize);
 90		/* These must be after realloc (u or v may be the same as w).  */
 91		up = u->d;
 92		vp = v->d;
 93	}
 94	wp = w->d;
 95	wsign = 0;
 96
 97	if (!vsize) {  /* simple */
 98		MPN_COPY(wp, up, usize);
 99		wsize = usize;
100		wsign = usign;
101	} else if (usign != vsign) { /* different sign */
102		/* This test is right since USIZE >= VSIZE */
103		if (usize != vsize) {
104			mpihelp_sub(wp, up, usize, vp, vsize);
105			wsize = usize;
106			MPN_NORMALIZE(wp, wsize);
107			wsign = usign;
108		} else if (mpihelp_cmp(up, vp, usize) < 0) {
109			mpihelp_sub_n(wp, vp, up, usize);
110			wsize = usize;
111			MPN_NORMALIZE(wp, wsize);
112			if (!usign)
113				wsign = 1;
114		} else {
115			mpihelp_sub_n(wp, up, vp, usize);
116			wsize = usize;
117			MPN_NORMALIZE(wp, wsize);
118			if (usign)
119				wsign = 1;
120		}
121	} else { /* U and V have same sign. Add them. */
122		mpi_limb_t cy = mpihelp_add(wp, up, usize, vp, vsize);
123		wp[usize] = cy;
124		wsize = usize + cy;
125		if (usign)
126			wsign = 1;
127	}
128
129	w->nlimbs = wsize;
130	w->sign = wsign;
131}
132EXPORT_SYMBOL_GPL(mpi_add);
133
134void mpi_sub(MPI w, MPI u, MPI v)
135{
136	MPI vv = mpi_copy(v);
137	vv->sign = !vv->sign;
138	mpi_add(w, u, vv);
139	mpi_free(vv);
140}
141
142
143void mpi_addm(MPI w, MPI u, MPI v, MPI m)
144{
145	mpi_add(w, u, v);
146	mpi_mod(w, w, m);
147}
148EXPORT_SYMBOL_GPL(mpi_addm);
149
150void mpi_subm(MPI w, MPI u, MPI v, MPI m)
151{
152	mpi_sub(w, u, v);
153	mpi_mod(w, w, m);
154}
155EXPORT_SYMBOL_GPL(mpi_subm);