1/* mpi-bit.c  -  MPI bit level functions
2 * Copyright (C) 1998, 1999 Free Software Foundation, Inc.
3 *
4 * This file is part of GnuPG.
5 *
6 * GnuPG is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * GnuPG is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
19 */
20
21#include "mpi-internal.h"
22#include "longlong.h"
23
24#define A_LIMB_1 ((mpi_limb_t) 1)
25
26/****************
27 * Sometimes we have MSL (most significant limbs) which are 0;
28 * this is for some reasons not good, so this function removes them.
29 */
30void mpi_normalize(MPI a)
31{
32	for (; a->nlimbs && !a->d[a->nlimbs - 1]; a->nlimbs--)
33		;
34}
35EXPORT_SYMBOL_GPL(mpi_normalize);
36
37/****************
38 * Return the number of bits in A.
39 */
40unsigned mpi_get_nbits(MPI a)
41{
42	unsigned n;
43
44	mpi_normalize(a);
45
46	if (a->nlimbs) {
47		mpi_limb_t alimb = a->d[a->nlimbs - 1];
48		if (alimb)
49			n = count_leading_zeros(alimb);
50		else
51			n = BITS_PER_MPI_LIMB;
52		n = BITS_PER_MPI_LIMB - n + (a->nlimbs - 1) * BITS_PER_MPI_LIMB;
53	} else
54		n = 0;
55	return n;
56}
57EXPORT_SYMBOL_GPL(mpi_get_nbits);
58
59/****************
60 * Test whether bit N is set.
61 */
62int mpi_test_bit(MPI a, unsigned int n)
63{
64	unsigned int limbno, bitno;
65	mpi_limb_t limb;
66
67	limbno = n / BITS_PER_MPI_LIMB;
68	bitno  = n % BITS_PER_MPI_LIMB;
69
70	if (limbno >= a->nlimbs)
71		return 0; /* too far left: this is a 0 */
72	limb = a->d[limbno];
73	return (limb & (A_LIMB_1 << bitno)) ? 1 : 0;
74}
75EXPORT_SYMBOL_GPL(mpi_test_bit);
76
77/****************
78 * Set bit N of A.
79 */
80void mpi_set_bit(MPI a, unsigned int n)
81{
82	unsigned int i, limbno, bitno;
83
84	limbno = n / BITS_PER_MPI_LIMB;
85	bitno  = n % BITS_PER_MPI_LIMB;
86
87	if (limbno >= a->nlimbs) {
88		for (i = a->nlimbs; i < a->alloced; i++)
89			a->d[i] = 0;
90		mpi_resize(a, limbno+1);
91		a->nlimbs = limbno+1;
92	}
93	a->d[limbno] |= (A_LIMB_1<<bitno);
94}
95
96/****************
97 * Set bit N of A. and clear all bits above
98 */
99void mpi_set_highbit(MPI a, unsigned int n)
100{
101	unsigned int i, limbno, bitno;
102
103	limbno = n / BITS_PER_MPI_LIMB;
104	bitno  = n % BITS_PER_MPI_LIMB;
105
106	if (limbno >= a->nlimbs) {
107		for (i = a->nlimbs; i < a->alloced; i++)
108			a->d[i] = 0;
109		mpi_resize(a, limbno+1);
110		a->nlimbs = limbno+1;
111	}
112	a->d[limbno] |= (A_LIMB_1<<bitno);
113	for (bitno++; bitno < BITS_PER_MPI_LIMB; bitno++)
114		a->d[limbno] &= ~(A_LIMB_1 << bitno);
115	a->nlimbs = limbno+1;
116}
117EXPORT_SYMBOL_GPL(mpi_set_highbit);
118
119/****************
120 * clear bit N of A and all bits above
121 */
122void mpi_clear_highbit(MPI a, unsigned int n)
123{
124	unsigned int limbno, bitno;
125
126	limbno = n / BITS_PER_MPI_LIMB;
127	bitno  = n % BITS_PER_MPI_LIMB;
128
129	if (limbno >= a->nlimbs)
130		return; /* not allocated, therefore no need to clear bits :-) */
131
132	for ( ; bitno < BITS_PER_MPI_LIMB; bitno++)
133		a->d[limbno] &= ~(A_LIMB_1 << bitno);
134	a->nlimbs = limbno+1;
135}
136
137/****************
138 * Clear bit N of A.
139 */
140void mpi_clear_bit(MPI a, unsigned int n)
141{
142	unsigned int limbno, bitno;
143
144	limbno = n / BITS_PER_MPI_LIMB;
145	bitno  = n % BITS_PER_MPI_LIMB;
146
147	if (limbno >= a->nlimbs)
148		return; /* Don't need to clear this bit, it's far too left.  */
149	a->d[limbno] &= ~(A_LIMB_1 << bitno);
150}
151EXPORT_SYMBOL_GPL(mpi_clear_bit);
152
153
154/****************
155 * Shift A by COUNT limbs to the right
156 * This is used only within the MPI library
157 */
158void mpi_rshift_limbs(MPI a, unsigned int count)
159{
160	mpi_ptr_t ap = a->d;
161	mpi_size_t n = a->nlimbs;
162	unsigned int i;
163
164	if (count >= n) {
165		a->nlimbs = 0;
166		return;
167	}
168
169	for (i = 0; i < n - count; i++)
170		ap[i] = ap[i+count];
171	ap[i] = 0;
172	a->nlimbs -= count;
173}
174
175/*
176 * Shift A by N bits to the right.
177 */
178void mpi_rshift(MPI x, MPI a, unsigned int n)
179{
180	mpi_size_t xsize;
181	unsigned int i;
182	unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
183	unsigned int nbits = (n%BITS_PER_MPI_LIMB);
184
185	if (x == a) {
186		/* In-place operation.  */
187		if (nlimbs >= x->nlimbs) {
188			x->nlimbs = 0;
189			return;
190		}
191
192		if (nlimbs) {
193			for (i = 0; i < x->nlimbs - nlimbs; i++)
194				x->d[i] = x->d[i+nlimbs];
195			x->d[i] = 0;
196			x->nlimbs -= nlimbs;
197		}
198		if (x->nlimbs && nbits)
199			mpihelp_rshift(x->d, x->d, x->nlimbs, nbits);
200	} else if (nlimbs) {
201		/* Copy and shift by more or equal bits than in a limb. */
202		xsize = a->nlimbs;
203		x->sign = a->sign;
204		RESIZE_IF_NEEDED(x, xsize);
205		x->nlimbs = xsize;
206		for (i = 0; i < a->nlimbs; i++)
207			x->d[i] = a->d[i];
208		x->nlimbs = i;
209
210		if (nlimbs >= x->nlimbs) {
211			x->nlimbs = 0;
212			return;
213		}
214
215		if (nlimbs) {
216			for (i = 0; i < x->nlimbs - nlimbs; i++)
217				x->d[i] = x->d[i+nlimbs];
218			x->d[i] = 0;
219			x->nlimbs -= nlimbs;
220		}
221
222		if (x->nlimbs && nbits)
223			mpihelp_rshift(x->d, x->d, x->nlimbs, nbits);
224	} else {
225		/* Copy and shift by less than bits in a limb.  */
226		xsize = a->nlimbs;
227		x->sign = a->sign;
228		RESIZE_IF_NEEDED(x, xsize);
229		x->nlimbs = xsize;
230
231		if (xsize) {
232			if (nbits)
233				mpihelp_rshift(x->d, a->d, x->nlimbs, nbits);
234			else {
235				/* The rshift helper function is not specified for
236				 * NBITS==0, thus we do a plain copy here.
237				 */
238				for (i = 0; i < x->nlimbs; i++)
239					x->d[i] = a->d[i];
240			}
241		}
242	}
243	MPN_NORMALIZE(x->d, x->nlimbs);
244}
245EXPORT_SYMBOL_GPL(mpi_rshift);
246
247/****************
248 * Shift A by COUNT limbs to the left
249 * This is used only within the MPI library
250 */
251void mpi_lshift_limbs(MPI a, unsigned int count)
252{
253	mpi_ptr_t ap;
254	int n = a->nlimbs;
255	int i;
256
257	if (!count || !n)
258		return;
259
260	RESIZE_IF_NEEDED(a, n+count);
261
262	ap = a->d;
263	for (i = n-1; i >= 0; i--)
264		ap[i+count] = ap[i];
265	for (i = 0; i < count; i++)
266		ap[i] = 0;
267	a->nlimbs += count;
268}
269
270/*
271 * Shift A by N bits to the left.
272 */
273void mpi_lshift(MPI x, MPI a, unsigned int n)
274{
275	unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
276	unsigned int nbits = (n%BITS_PER_MPI_LIMB);
277
278	if (x == a && !n)
279		return;  /* In-place shift with an amount of zero.  */
280
281	if (x != a) {
282		/* Copy A to X.  */
283		unsigned int alimbs = a->nlimbs;
284		int asign = a->sign;
285		mpi_ptr_t xp, ap;
286
287		RESIZE_IF_NEEDED(x, alimbs+nlimbs+1);
288		xp = x->d;
289		ap = a->d;
290		MPN_COPY(xp, ap, alimbs);
291		x->nlimbs = alimbs;
292		x->flags = a->flags;
293		x->sign = asign;
294	}
295
296	if (nlimbs && !nbits) {
297		/* Shift a full number of limbs.  */
298		mpi_lshift_limbs(x, nlimbs);
299	} else if (n) {
300		/* We use a very dump approach: Shift left by the number of
301		 * limbs plus one and than fix it up by an rshift.
302		 */
303		mpi_lshift_limbs(x, nlimbs+1);
304		mpi_rshift(x, x, BITS_PER_MPI_LIMB - nbits);
305	}
306
307	MPN_NORMALIZE(x->d, x->nlimbs);
308}
309