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 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 it 12 under the terms of the GNU Lesser General Public License as published by the 13 Free Software Foundation; either version 3 of the License, or (at your 14 option) any later version. 15 16 The GNU MP Library is distributed in the hope that it will be useful, but 17 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 18 FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License 19 for more details. 20 21 You should have received a copy of the GNU Lesser General Public License along 22 with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 23 24 25 #include "gmp.h" 26 #include "gmp-impl.h" 27 #include "longlong.h" 28 29 mp_size_t 30 mpn_pow_1 (mp_ptr rp, mp_srcptr bp, mp_size_t bn, mp_limb_t exp, mp_ptr tp) 31 { 32 mp_limb_t x; 33 int cnt, i; 34 mp_size_t rn; 35 int par; 36 37 ASSERT (bn >= 1); 38 /* FIXME: Add operand overlap criteria */ 39 40 if (exp <= 1) 41 { 42 if (exp == 0) 43 { 44 rp[0] = 1; 45 return 1; 46 } 47 else 48 { 49 MPN_COPY (rp, bp, bn); 50 return bn; 51 } 52 } 53 54 /* Count number of bits in exp, and compute where to put initial square in 55 order to magically get results in the entry rp. Use simple code, 56 optimized for small exp. For large exp, the bignum operations will take 57 so much time that the slowness of this code will be negligible. */ 58 par = 0; 59 cnt = GMP_LIMB_BITS; 60 for (x = exp; x != 0; x >>= 1) 61 { 62 par ^= x & 1; 63 cnt--; 64 } 65 exp <<= cnt; 66 67 if (bn == 1) 68 { 69 mp_limb_t bl = bp[0]; 70 71 if ((cnt & 1) != 0) 72 MP_PTR_SWAP (rp, tp); 73 74 mpn_sqr (rp, bp, bn); 75 rn = 2 * bn; rn -= rp[rn - 1] == 0; 76 77 for (i = GMP_LIMB_BITS - cnt - 1;;) 78 { 79 exp <<= 1; 80 if ((exp & GMP_LIMB_HIGHBIT) != 0) 81 { 82 rp[rn] = mpn_mul_1 (rp, rp, rn, bl); 83 rn += rp[rn] != 0; 84 } 85 86 if (--i == 0) 87 break; 88 89 mpn_sqr (tp, rp, rn); 90 rn = 2 * rn; rn -= tp[rn - 1] == 0; 91 MP_PTR_SWAP (rp, tp); 92 } 93 } 94 else 95 { 96 if (((par ^ cnt) & 1) == 0) 97 MP_PTR_SWAP (rp, tp); 98 99 mpn_sqr (rp, bp, bn); 100 rn = 2 * bn; rn -= rp[rn - 1] == 0; 101 102 for (i = GMP_LIMB_BITS - cnt - 1;;) 103 { 104 exp <<= 1; 105 if ((exp & GMP_LIMB_HIGHBIT) != 0) 106 { 107 rn = rn + bn - (mpn_mul (tp, rp, rn, bp, bn) == 0); 108 MP_PTR_SWAP (rp, tp); 109 } 110 111 if (--i == 0) 112 break; 113 114 mpn_sqr (tp, rp, rn); 115 rn = 2 * rn; rn -= tp[rn - 1] == 0; 116 MP_PTR_SWAP (rp, tp); 117 } 118 } 119 120 return rn; 121 } 122