Annotation of OpenXM_contrib/gmp/mpz/powm_ui.c, Revision 1.1.1.2
1.1 maekawa 1: /* mpz_powm_ui(res,base,exp,mod) -- Set RES to (base**exp) mod MOD.
2:
1.1.1.2 ! maekawa 3: Copyright (C) 1991, 1993, 1994, 1996, 1997, 2000 Free Software Foundation,
! 4: Inc.
1.1 maekawa 5:
6: This file is part of the GNU MP Library.
7:
8: The GNU MP Library is free software; you can redistribute it and/or modify
1.1.1.2 ! maekawa 9: it under the terms of the GNU Lesser General Public License as published by
! 10: the Free Software Foundation; either version 2.1 of the License, or (at your
1.1 maekawa 11: option) any later version.
12:
13: The GNU MP Library is distributed in the hope that it will be useful, but
14: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
1.1.1.2 ! maekawa 15: or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
1.1 maekawa 16: License for more details.
17:
1.1.1.2 ! maekawa 18: You should have received a copy of the GNU Lesser General Public License
1.1 maekawa 19: along with the GNU MP Library; see the file COPYING.LIB. If not, write to
20: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
21: MA 02111-1307, USA. */
22:
1.1.1.2 ! maekawa 23: #include <stdio.h> /* for NULL */
1.1 maekawa 24: #include "gmp.h"
25: #include "gmp-impl.h"
26: #include "longlong.h"
27:
28: void
29: #if __STDC__
30: mpz_powm_ui (mpz_ptr res, mpz_srcptr base, unsigned long int exp, mpz_srcptr mod)
31: #else
32: mpz_powm_ui (res, base, exp, mod)
33: mpz_ptr res;
34: mpz_srcptr base;
35: unsigned long int exp;
36: mpz_srcptr mod;
37: #endif
38: {
39: mp_ptr rp, mp, bp;
40: mp_size_t msize, bsize, rsize;
41: mp_size_t size;
42: int mod_shift_cnt;
43: int negative_result;
44: mp_limb_t *free_me = NULL;
45: size_t free_me_size;
46: TMP_DECL (marker);
47:
48: msize = ABS (mod->_mp_size);
49: size = 2 * msize;
50:
51: rp = res->_mp_d;
52:
53: if (msize == 0)
1.1.1.2 ! maekawa 54: DIVIDE_BY_ZERO;
1.1 maekawa 55:
56: if (exp == 0)
57: {
1.1.1.2 ! maekawa 58: /* Exponent is zero, result is 1 mod MOD, i.e., 1 or 0
! 59: depending on if MOD equals 1. */
1.1 maekawa 60: res->_mp_size = (msize == 1 && (mod->_mp_d)[0] == 1) ? 0 : 1;
1.1.1.2 ! maekawa 61: rp[0] = 1;
1.1 maekawa 62: return;
63: }
64:
65: TMP_MARK (marker);
66:
67: /* Normalize MOD (i.e. make its most significant bit set) as required by
68: mpn_divmod. This will make the intermediate values in the calculation
69: slightly larger, but the correct result is obtained after a final
70: reduction using the original MOD value. */
71:
72: mp = (mp_ptr) TMP_ALLOC (msize * BYTES_PER_MP_LIMB);
73: count_leading_zeros (mod_shift_cnt, mod->_mp_d[msize - 1]);
74: if (mod_shift_cnt != 0)
75: mpn_lshift (mp, mod->_mp_d, msize, mod_shift_cnt);
76: else
77: MPN_COPY (mp, mod->_mp_d, msize);
78:
79: bsize = ABS (base->_mp_size);
80: if (bsize > msize)
81: {
82: /* The base is larger than the module. Reduce it. */
83:
84: /* Allocate (BSIZE + 1) with space for remainder and quotient.
85: (The quotient is (bsize - msize + 1) limbs.) */
86: bp = (mp_ptr) TMP_ALLOC ((bsize + 1) * BYTES_PER_MP_LIMB);
87: MPN_COPY (bp, base->_mp_d, bsize);
88: /* We don't care about the quotient, store it above the remainder,
89: at BP + MSIZE. */
90: mpn_divmod (bp + msize, bp, bsize, mp, msize);
91: bsize = msize;
92: /* Canonicalize the base, since we are going to multiply with it
93: quite a few times. */
94: MPN_NORMALIZE (bp, bsize);
95: }
96: else
97: bp = base->_mp_d;
98:
99: if (bsize == 0)
100: {
101: res->_mp_size = 0;
102: TMP_FREE (marker);
103: return;
104: }
105:
106: if (res->_mp_alloc < size)
107: {
108: /* We have to allocate more space for RES. If any of the input
109: parameters are identical to RES, defer deallocation of the old
110: space. */
111:
112: if (rp == mp || rp == bp)
113: {
114: free_me = rp;
115: free_me_size = res->_mp_alloc;
116: }
117: else
118: (*_mp_free_func) (rp, res->_mp_alloc * BYTES_PER_MP_LIMB);
119:
120: rp = (mp_ptr) (*_mp_allocate_func) (size * BYTES_PER_MP_LIMB);
121: res->_mp_alloc = size;
122: res->_mp_d = rp;
123: }
124: else
125: {
126: /* Make BASE, EXP and MOD not overlap with RES. */
127: if (rp == bp)
128: {
129: /* RES and BASE are identical. Allocate temp. space for BASE. */
130: bp = (mp_ptr) TMP_ALLOC (bsize * BYTES_PER_MP_LIMB);
131: MPN_COPY (bp, rp, bsize);
132: }
133: if (rp == mp)
134: {
135: /* RES and MOD are identical. Allocate temporary space for MOD. */
136: mp = (mp_ptr) TMP_ALLOC (msize * BYTES_PER_MP_LIMB);
137: MPN_COPY (mp, rp, msize);
138: }
139: }
140:
141: MPN_COPY (rp, bp, bsize);
142: rsize = bsize;
143:
144: {
145: mp_ptr xp = (mp_ptr) TMP_ALLOC (2 * (msize + 1) * BYTES_PER_MP_LIMB);
146: int c;
147: mp_limb_t e;
148: mp_limb_t carry_limb;
149:
150: negative_result = (exp & 1) && base->_mp_size < 0;
151:
152: e = exp;
153: count_leading_zeros (c, e);
154: e = (e << c) << 1; /* shift the exp bits to the left, lose msb */
155: c = BITS_PER_MP_LIMB - 1 - c;
156:
157: /* Main loop.
158:
159: Make the result be pointed to alternately by XP and RP. This
160: helps us avoid block copying, which would otherwise be necessary
161: with the overlap restrictions of mpn_divmod. With 50% probability
162: the result after this loop will be in the area originally pointed
163: by RP (==RES->_mp_d), and with 50% probability in the area originally
164: pointed to by XP. */
165:
166: while (c != 0)
167: {
168: mp_ptr tp;
169: mp_size_t xsize;
170:
171: mpn_mul_n (xp, rp, rp, rsize);
172: xsize = 2 * rsize;
1.1.1.2 ! maekawa 173: xsize -= xp[xsize - 1] == 0;
1.1 maekawa 174: if (xsize > msize)
175: {
176: mpn_divmod (xp + msize, xp, xsize, mp, msize);
177: xsize = msize;
178: }
179:
180: tp = rp; rp = xp; xp = tp;
181: rsize = xsize;
182:
183: if ((mp_limb_signed_t) e < 0)
184: {
185: mpn_mul (xp, rp, rsize, bp, bsize);
186: xsize = rsize + bsize;
1.1.1.2 ! maekawa 187: xsize -= xp[xsize - 1] == 0;
1.1 maekawa 188: if (xsize > msize)
189: {
190: mpn_divmod (xp + msize, xp, xsize, mp, msize);
191: xsize = msize;
192: }
193:
194: tp = rp; rp = xp; xp = tp;
195: rsize = xsize;
196: }
197: e <<= 1;
198: c--;
199: }
200:
201: /* We shifted MOD, the modulo reduction argument, left MOD_SHIFT_CNT
202: steps. Adjust the result by reducing it with the original MOD.
203:
204: Also make sure the result is put in RES->_mp_d (where it already
205: might be, see above). */
206:
207: if (mod_shift_cnt != 0)
208: {
209: carry_limb = mpn_lshift (res->_mp_d, rp, rsize, mod_shift_cnt);
210: rp = res->_mp_d;
211: if (carry_limb != 0)
212: {
213: rp[rsize] = carry_limb;
214: rsize++;
215: }
216: }
217: else
218: {
219: MPN_COPY (res->_mp_d, rp, rsize);
220: rp = res->_mp_d;
221: }
222:
223: if (rsize >= msize)
224: {
225: mpn_divmod (rp + msize, rp, rsize, mp, msize);
226: rsize = msize;
227: }
228:
229: /* Remove any leading zero words from the result. */
230: if (mod_shift_cnt != 0)
231: mpn_rshift (rp, rp, rsize, mod_shift_cnt);
232: MPN_NORMALIZE (rp, rsize);
233: }
234:
1.1.1.2 ! maekawa 235: if (negative_result && rsize != 0)
! 236: {
! 237: if (mod_shift_cnt != 0)
! 238: mpn_rshift (mp, mp, msize, mod_shift_cnt);
! 239: mpn_sub (rp, mp, msize, rp, rsize);
! 240: rsize = msize;
! 241: MPN_NORMALIZE (rp, rsize);
! 242: }
! 243: res->_mp_size = rsize;
1.1 maekawa 244:
245: if (free_me != NULL)
246: (*_mp_free_func) (free_me, free_me_size * BYTES_PER_MP_LIMB);
247: TMP_FREE (marker);
248: }
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