1 /* mpn_pow_1 -- Compute powers R = U^exp. 2 3 THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE ONLY. THEY'RE ALMOST 4 CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR COMPLETELY IN 5 FUTURE GNU MP RELEASES. 6 7 Copyright 2002, 2014 Free Software Foundation, Inc. 8 9 This file is part of the GNU MP Library. 10 11 The GNU MP Library is free software; you can redistribute it and/or modify 12 it under the terms of either: 13 14 * the GNU Lesser General Public License as published by the Free 15 Software Foundation; either version 3 of the License, or (at your 16 option) any later version. 17 18 or 19 20 * the GNU General Public License as published by the Free Software 21 Foundation; either version 2 of the License, or (at your option) any 22 later version. 23 24 or both in parallel, as here. 25 26 The GNU MP Library is distributed in the hope that it will be useful, but 27 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 28 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 29 for more details. 30 31 You should have received copies of the GNU General Public License and the 32 GNU Lesser General Public License along with the GNU MP Library. If not, 33 see https://www.gnu.org/licenses/. */ 34 35 36 #include "gmp-impl.h" 37 #include "longlong.h" 38 39 mp_size_t 40 mpn_pow_1 (mp_ptr rp, mp_srcptr bp, mp_size_t bn, mp_limb_t exp, mp_ptr tp) 41 { 42 mp_limb_t x; 43 int cnt, i; 44 mp_size_t rn; 45 int par; 46 47 ASSERT (bn >= 1); 48 /* FIXME: Add operand overlap criteria */ 49 50 if (exp <= 1) 51 { 52 if (exp == 0) 53 { 54 rp[0] = 1; 55 return 1; 56 } 57 else 58 { 59 MPN_COPY (rp, bp, bn); 60 return bn; 61 } 62 } 63 64 /* Count number of bits in exp, and compute where to put initial square in 65 order to magically get results in the entry rp. Use simple code, 66 optimized for small exp. For large exp, the bignum operations will take 67 so much time that the slowness of this code will be negligible. */ 68 par = 0; 69 cnt = GMP_LIMB_BITS; 70 x = exp; 71 do 72 { 73 par ^= x; 74 cnt--; 75 x >>= 1; 76 } while (x != 0); 77 exp <<= cnt; 78 79 if (bn == 1) 80 { 81 mp_limb_t rl, rh, bl = bp[0]; 82 83 if ((cnt & 1) != 0) 84 MP_PTR_SWAP (rp, tp); 85 86 umul_ppmm (rh, rl, bl, bl << GMP_NAIL_BITS); 87 rp[0] = rl >> GMP_NAIL_BITS; 88 rp[1] = rh; 89 rn = 1 + (rh != 0); 90 91 for (i = GMP_LIMB_BITS - cnt - 1;;) 92 { 93 exp <<= 1; 94 if ((exp & GMP_LIMB_HIGHBIT) != 0) 95 { 96 rp[rn] = rh = mpn_mul_1 (rp, rp, rn, bl); 97 rn += rh != 0; 98 } 99 100 if (--i == 0) 101 break; 102 103 mpn_sqr (tp, rp, rn); 104 rn = 2 * rn; rn -= tp[rn - 1] == 0; 105 MP_PTR_SWAP (rp, tp); 106 } 107 } 108 else 109 { 110 if (((par ^ cnt) & 1) == 0) 111 MP_PTR_SWAP (rp, tp); 112 113 mpn_sqr (rp, bp, bn); 114 rn = 2 * bn; rn -= rp[rn - 1] == 0; 115 116 for (i = GMP_LIMB_BITS - cnt - 1;;) 117 { 118 exp <<= 1; 119 if ((exp & GMP_LIMB_HIGHBIT) != 0) 120 { 121 rn = rn + bn - (mpn_mul (tp, rp, rn, bp, bn) == 0); 122 MP_PTR_SWAP (rp, tp); 123 } 124 125 if (--i == 0) 126 break; 127 128 mpn_sqr (tp, rp, rn); 129 rn = 2 * rn; rn -= tp[rn - 1] == 0; 130 MP_PTR_SWAP (rp, tp); 131 } 132 } 133 134 return rn; 135 } 136