Annotation of OpenXM/src/kan96xx/gmp-2.0.2/mpz/powm_ui.c, Revision 1.1
1.1 ! maekawa 1: /* mpz_powm_ui(res,base,exp,mod) -- Set RES to (base**exp) mod MOD.
! 2:
! 3: Copyright (C) 1991, 1993, 1994, 1996 Free Software Foundation, Inc.
! 4:
! 5: This file is part of the GNU MP Library.
! 6:
! 7: The GNU MP Library is free software; you can redistribute it and/or modify
! 8: it under the terms of the GNU Library General Public License as published by
! 9: the Free Software Foundation; either version 2 of the License, or (at your
! 10: option) any later version.
! 11:
! 12: The GNU MP Library is distributed in the hope that it will be useful, but
! 13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
! 14: or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
! 15: License for more details.
! 16:
! 17: You should have received a copy of the GNU Library General Public License
! 18: along with the GNU MP Library; see the file COPYING.LIB. If not, write to
! 19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
! 20: MA 02111-1307, USA. */
! 21:
! 22: #include "gmp.h"
! 23: #include "gmp-impl.h"
! 24: #include "longlong.h"
! 25:
! 26: void
! 27: #if __STDC__
! 28: mpz_powm_ui (mpz_ptr res, mpz_srcptr base, unsigned long int exp, mpz_srcptr mod)
! 29: #else
! 30: mpz_powm_ui (res, base, exp, mod)
! 31: mpz_ptr res;
! 32: mpz_srcptr base;
! 33: unsigned long int exp;
! 34: mpz_srcptr mod;
! 35: #endif
! 36: {
! 37: mp_ptr rp, mp, bp;
! 38: mp_size_t msize, bsize, rsize;
! 39: mp_size_t size;
! 40: int mod_shift_cnt;
! 41: int negative_result;
! 42: mp_limb_t *free_me = NULL;
! 43: size_t free_me_size;
! 44: TMP_DECL (marker);
! 45:
! 46: msize = ABS (mod->_mp_size);
! 47: size = 2 * msize;
! 48:
! 49: rp = res->_mp_d;
! 50:
! 51: if (msize == 0)
! 52: msize = 1 / msize; /* provoke a signal */
! 53:
! 54: if (exp == 0)
! 55: {
! 56: rp[0] = 1;
! 57: res->_mp_size = (msize == 1 && (mod->_mp_d)[0] == 1) ? 0 : 1;
! 58: return;
! 59: }
! 60:
! 61: TMP_MARK (marker);
! 62:
! 63: /* Normalize MOD (i.e. make its most significant bit set) as required by
! 64: mpn_divmod. This will make the intermediate values in the calculation
! 65: slightly larger, but the correct result is obtained after a final
! 66: reduction using the original MOD value. */
! 67:
! 68: mp = (mp_ptr) TMP_ALLOC (msize * BYTES_PER_MP_LIMB);
! 69: count_leading_zeros (mod_shift_cnt, mod->_mp_d[msize - 1]);
! 70: if (mod_shift_cnt != 0)
! 71: mpn_lshift (mp, mod->_mp_d, msize, mod_shift_cnt);
! 72: else
! 73: MPN_COPY (mp, mod->_mp_d, msize);
! 74:
! 75: bsize = ABS (base->_mp_size);
! 76: if (bsize > msize)
! 77: {
! 78: /* The base is larger than the module. Reduce it. */
! 79:
! 80: /* Allocate (BSIZE + 1) with space for remainder and quotient.
! 81: (The quotient is (bsize - msize + 1) limbs.) */
! 82: bp = (mp_ptr) TMP_ALLOC ((bsize + 1) * BYTES_PER_MP_LIMB);
! 83: MPN_COPY (bp, base->_mp_d, bsize);
! 84: /* We don't care about the quotient, store it above the remainder,
! 85: at BP + MSIZE. */
! 86: mpn_divmod (bp + msize, bp, bsize, mp, msize);
! 87: bsize = msize;
! 88: /* Canonicalize the base, since we are going to multiply with it
! 89: quite a few times. */
! 90: MPN_NORMALIZE (bp, bsize);
! 91: }
! 92: else
! 93: bp = base->_mp_d;
! 94:
! 95: if (bsize == 0)
! 96: {
! 97: res->_mp_size = 0;
! 98: TMP_FREE (marker);
! 99: return;
! 100: }
! 101:
! 102: if (res->_mp_alloc < size)
! 103: {
! 104: /* We have to allocate more space for RES. If any of the input
! 105: parameters are identical to RES, defer deallocation of the old
! 106: space. */
! 107:
! 108: if (rp == mp || rp == bp)
! 109: {
! 110: free_me = rp;
! 111: free_me_size = res->_mp_alloc;
! 112: }
! 113: else
! 114: (*_mp_free_func) (rp, res->_mp_alloc * BYTES_PER_MP_LIMB);
! 115:
! 116: rp = (mp_ptr) (*_mp_allocate_func) (size * BYTES_PER_MP_LIMB);
! 117: res->_mp_alloc = size;
! 118: res->_mp_d = rp;
! 119: }
! 120: else
! 121: {
! 122: /* Make BASE, EXP and MOD not overlap with RES. */
! 123: if (rp == bp)
! 124: {
! 125: /* RES and BASE are identical. Allocate temp. space for BASE. */
! 126: bp = (mp_ptr) TMP_ALLOC (bsize * BYTES_PER_MP_LIMB);
! 127: MPN_COPY (bp, rp, bsize);
! 128: }
! 129: if (rp == mp)
! 130: {
! 131: /* RES and MOD are identical. Allocate temporary space for MOD. */
! 132: mp = (mp_ptr) TMP_ALLOC (msize * BYTES_PER_MP_LIMB);
! 133: MPN_COPY (mp, rp, msize);
! 134: }
! 135: }
! 136:
! 137: MPN_COPY (rp, bp, bsize);
! 138: rsize = bsize;
! 139:
! 140: {
! 141: mp_ptr xp = (mp_ptr) TMP_ALLOC (2 * (msize + 1) * BYTES_PER_MP_LIMB);
! 142: int c;
! 143: mp_limb_t e;
! 144: mp_limb_t carry_limb;
! 145:
! 146: negative_result = (exp & 1) && base->_mp_size < 0;
! 147:
! 148: e = exp;
! 149: count_leading_zeros (c, e);
! 150: e = (e << c) << 1; /* shift the exp bits to the left, lose msb */
! 151: c = BITS_PER_MP_LIMB - 1 - c;
! 152:
! 153: /* Main loop.
! 154:
! 155: Make the result be pointed to alternately by XP and RP. This
! 156: helps us avoid block copying, which would otherwise be necessary
! 157: with the overlap restrictions of mpn_divmod. With 50% probability
! 158: the result after this loop will be in the area originally pointed
! 159: by RP (==RES->_mp_d), and with 50% probability in the area originally
! 160: pointed to by XP. */
! 161:
! 162: while (c != 0)
! 163: {
! 164: mp_ptr tp;
! 165: mp_size_t xsize;
! 166:
! 167: mpn_mul_n (xp, rp, rp, rsize);
! 168: xsize = 2 * rsize;
! 169: if (xsize > msize)
! 170: {
! 171: mpn_divmod (xp + msize, xp, xsize, mp, msize);
! 172: xsize = msize;
! 173: }
! 174:
! 175: tp = rp; rp = xp; xp = tp;
! 176: rsize = xsize;
! 177:
! 178: if ((mp_limb_signed_t) e < 0)
! 179: {
! 180: mpn_mul (xp, rp, rsize, bp, bsize);
! 181: xsize = rsize + bsize;
! 182: if (xsize > msize)
! 183: {
! 184: mpn_divmod (xp + msize, xp, xsize, mp, msize);
! 185: xsize = msize;
! 186: }
! 187:
! 188: tp = rp; rp = xp; xp = tp;
! 189: rsize = xsize;
! 190: }
! 191: e <<= 1;
! 192: c--;
! 193: }
! 194:
! 195: /* We shifted MOD, the modulo reduction argument, left MOD_SHIFT_CNT
! 196: steps. Adjust the result by reducing it with the original MOD.
! 197:
! 198: Also make sure the result is put in RES->_mp_d (where it already
! 199: might be, see above). */
! 200:
! 201: if (mod_shift_cnt != 0)
! 202: {
! 203: carry_limb = mpn_lshift (res->_mp_d, rp, rsize, mod_shift_cnt);
! 204: rp = res->_mp_d;
! 205: if (carry_limb != 0)
! 206: {
! 207: rp[rsize] = carry_limb;
! 208: rsize++;
! 209: }
! 210: }
! 211: else
! 212: {
! 213: MPN_COPY (res->_mp_d, rp, rsize);
! 214: rp = res->_mp_d;
! 215: }
! 216:
! 217: if (rsize >= msize)
! 218: {
! 219: mpn_divmod (rp + msize, rp, rsize, mp, msize);
! 220: rsize = msize;
! 221: }
! 222:
! 223: /* Remove any leading zero words from the result. */
! 224: if (mod_shift_cnt != 0)
! 225: mpn_rshift (rp, rp, rsize, mod_shift_cnt);
! 226: MPN_NORMALIZE (rp, rsize);
! 227: }
! 228:
! 229: res->_mp_size = negative_result == 0 ? rsize : -rsize;
! 230:
! 231: if (free_me != NULL)
! 232: (*_mp_free_func) (free_me, free_me_size * BYTES_PER_MP_LIMB);
! 233: TMP_FREE (marker);
! 234: }
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