--- /dev/null
+/* mpz_powm_ui(res,base,exp,mod) -- Set RES to (base**exp) mod MOD.
+
+Copyright 1991, 1993, 1994, 1996, 1997, 2000, 2001, 2002, 2005 Free Software
+Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 3 of the License, or (at your
+option) any later version.
+
+The GNU MP Library is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
+
+
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "longlong.h"
+
+/* Compute t = a mod m, a is defined by (ap,an), m is defined by (mp,mn), and
+ t is defined by (tp,mn). */
+static void
+reduce (mp_ptr tp, mp_srcptr ap, mp_size_t an, mp_srcptr mp, mp_size_t mn)
+{
+ mp_ptr qp;
+ TMP_DECL;
+
+ TMP_MARK;
+ qp = TMP_ALLOC_LIMBS (an - mn + 1);
+
+ mpn_tdiv_qr (qp, tp, 0L, ap, an, mp, mn);
+
+ TMP_FREE;
+}
+
+void
+mpz_powm_ui (mpz_ptr r, mpz_srcptr b, unsigned long int el, mpz_srcptr m)
+{
+ mp_ptr xp, tp, qp, mp, bp;
+ mp_size_t xn, tn, mn, bn;
+ int m_zero_cnt;
+ int c;
+ mp_limb_t e;
+ TMP_DECL;
+
+ mp = PTR(m);
+ mn = ABSIZ(m);
+ if (mn == 0)
+ DIVIDE_BY_ZERO;
+
+ if (el == 0)
+ {
+ /* Exponent is zero, result is 1 mod MOD, i.e., 1 or 0
+ depending on if MOD equals 1. */
+ SIZ(r) = (mn == 1 && mp[0] == 1) ? 0 : 1;
+ PTR(r)[0] = 1;
+ return;
+ }
+
+ TMP_MARK;
+
+ /* Normalize m (i.e. make its most significant bit set) as required by
+ division functions below. */
+ count_leading_zeros (m_zero_cnt, mp[mn - 1]);
+ m_zero_cnt -= GMP_NAIL_BITS;
+ if (m_zero_cnt != 0)
+ {
+ mp_ptr new_mp = TMP_ALLOC_LIMBS (mn);
+ mpn_lshift (new_mp, mp, mn, m_zero_cnt);
+ mp = new_mp;
+ }
+
+ bn = ABSIZ(b);
+ bp = PTR(b);
+ if (bn > mn)
+ {
+ /* Reduce possibly huge base. Use a function call to reduce, since we
+ don't want the quotient allocation to live until function return. */
+ mp_ptr new_bp = TMP_ALLOC_LIMBS (mn);
+ reduce (new_bp, bp, bn, mp, mn);
+ bp = new_bp;
+ bn = mn;
+ /* Canonicalize the base, since we are potentially going to multiply with
+ it quite a few times. */
+ MPN_NORMALIZE (bp, bn);
+ }
+
+ if (bn == 0)
+ {
+ SIZ(r) = 0;
+ TMP_FREE;
+ return;
+ }
+
+ tp = TMP_ALLOC_LIMBS (2 * mn + 1);
+ xp = TMP_ALLOC_LIMBS (mn);
+
+ qp = TMP_ALLOC_LIMBS (mn + 1);
+
+ MPN_COPY (xp, bp, bn);
+ xn = bn;
+
+ e = el;
+ count_leading_zeros (c, e);
+ e = (e << c) << 1; /* shift the exp bits to the left, lose msb */
+ c = BITS_PER_MP_LIMB - 1 - c;
+
+ /* Main loop. */
+
+ /* If m is already normalized (high bit of high limb set), and b is the
+ same size, but a bigger value, and e==1, then there's no modular
+ reductions done and we can end up with a result out of range at the
+ end. */
+ if (c == 0)
+ {
+ if (xn == mn && mpn_cmp (xp, mp, mn) >= 0)
+ mpn_sub_n (xp, xp, mp, mn);
+ goto finishup;
+ }
+
+ while (c != 0)
+ {
+ mpn_sqr_n (tp, xp, xn);
+ tn = 2 * xn; tn -= tp[tn - 1] == 0;
+ if (tn < mn)
+ {
+ MPN_COPY (xp, tp, tn);
+ xn = tn;
+ }
+ else
+ {
+ mpn_tdiv_qr (qp, xp, 0L, tp, tn, mp, mn);
+ xn = mn;
+ }
+
+ if ((mp_limb_signed_t) e < 0)
+ {
+ mpn_mul (tp, xp, xn, bp, bn);
+ tn = xn + bn; tn -= tp[tn - 1] == 0;
+ if (tn < mn)
+ {
+ MPN_COPY (xp, tp, tn);
+ xn = tn;
+ }
+ else
+ {
+ mpn_tdiv_qr (qp, xp, 0L, tp, tn, mp, mn);
+ xn = mn;
+ }
+ }
+ e <<= 1;
+ c--;
+ }
+
+ finishup:
+ /* We shifted m left m_zero_cnt steps. Adjust the result by reducing
+ it with the original MOD. */
+ if (m_zero_cnt != 0)
+ {
+ mp_limb_t cy;
+ cy = mpn_lshift (tp, xp, xn, m_zero_cnt);
+ tp[xn] = cy; xn += cy != 0;
+
+ if (xn < mn)
+ {
+ MPN_COPY (xp, tp, xn);
+ }
+ else
+ {
+ mpn_tdiv_qr (qp, xp, 0L, tp, xn, mp, mn);
+ xn = mn;
+ }
+ mpn_rshift (xp, xp, xn, m_zero_cnt);
+ }
+ MPN_NORMALIZE (xp, xn);
+
+ if ((el & 1) != 0 && SIZ(b) < 0 && xn != 0)
+ {
+ mp = PTR(m); /* want original, unnormalized m */
+ mpn_sub (xp, mp, mn, xp, xn);
+ xn = mn;
+ MPN_NORMALIZE (xp, xn);
+ }
+ MPZ_REALLOC (r, xn);
+ SIZ (r) = xn;
+ MPN_COPY (PTR(r), xp, xn);
+
+ TMP_FREE;
+}
projects / msp430-gcc.git / blobdiff