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136 lines
3.0 KiB
C
136 lines
3.0 KiB
C
/* mpn_pow_1 -- Compute powers R = U^exp.
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THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE ONLY. THEY'RE ALMOST
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CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR COMPLETELY IN
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FUTURE GNU MP RELEASES.
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Copyright 2002, 2014 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of either:
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* the GNU Lesser General Public License as published by the Free
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Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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or
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* the GNU General Public License as published by the Free Software
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Foundation; either version 2 of the License, or (at your option) any
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later version.
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or both in parallel, as here.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received copies of the GNU General Public License and the
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GNU Lesser General Public License along with the GNU MP Library. If not,
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see https://www.gnu.org/licenses/. */
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#include "gmp-impl.h"
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#include "longlong.h"
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mp_size_t
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mpn_pow_1 (mp_ptr rp, mp_srcptr bp, mp_size_t bn, mp_limb_t exp, mp_ptr tp)
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{
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mp_limb_t x;
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int cnt, i;
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mp_size_t rn;
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int par;
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ASSERT (bn >= 1);
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/* FIXME: Add operand overlap criteria */
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if (exp <= 1)
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{
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if (exp == 0)
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{
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rp[0] = 1;
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return 1;
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}
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else
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{
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MPN_COPY (rp, bp, bn);
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return bn;
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}
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}
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/* Count number of bits in exp, and compute where to put initial square in
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order to magically get results in the entry rp. Use simple code,
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optimized for small exp. For large exp, the bignum operations will take
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so much time that the slowness of this code will be negligible. */
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par = 0;
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cnt = GMP_LIMB_BITS;
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x = exp;
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do
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{
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par ^= x;
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cnt--;
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x >>= 1;
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} while (x != 0);
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exp <<= cnt;
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if (bn == 1)
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{
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mp_limb_t rl, rh, bl = bp[0];
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if ((cnt & 1) != 0)
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MP_PTR_SWAP (rp, tp);
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umul_ppmm (rh, rl, bl, bl << GMP_NAIL_BITS);
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rp[0] = rl >> GMP_NAIL_BITS;
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rp[1] = rh;
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rn = 1 + (rh != 0);
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for (i = GMP_LIMB_BITS - cnt - 1;;)
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{
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exp <<= 1;
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if ((exp & GMP_LIMB_HIGHBIT) != 0)
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{
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rp[rn] = rh = mpn_mul_1 (rp, rp, rn, bl);
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rn += rh != 0;
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}
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if (--i == 0)
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break;
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mpn_sqr (tp, rp, rn);
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rn = 2 * rn; rn -= tp[rn - 1] == 0;
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MP_PTR_SWAP (rp, tp);
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}
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}
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else
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{
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if (((par ^ cnt) & 1) == 0)
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MP_PTR_SWAP (rp, tp);
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mpn_sqr (rp, bp, bn);
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rn = 2 * bn; rn -= rp[rn - 1] == 0;
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for (i = GMP_LIMB_BITS - cnt - 1;;)
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{
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exp <<= 1;
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if ((exp & GMP_LIMB_HIGHBIT) != 0)
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{
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rn = rn + bn - (mpn_mul (tp, rp, rn, bp, bn) == 0);
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MP_PTR_SWAP (rp, tp);
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}
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if (--i == 0)
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break;
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mpn_sqr (tp, rp, rn);
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rn = 2 * rn; rn -= tp[rn - 1] == 0;
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MP_PTR_SWAP (rp, tp);
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}
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}
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return rn;
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}
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