1 /* mpfr_random2 -- Generate a positive random mpfr_t of specified size, with 2 long runs of consecutive ones and zeros in the binary representation. 3 4 Copyright 1999, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc. 5 Contributed by the Arenaire and Cacao projects, INRIA. 6 7 This file is part of the GNU MPFR Library. 8 9 The GNU MPFR Library is free software; you can redistribute it and/or modify 10 it under the terms of the GNU Lesser General Public License as published by 11 the Free Software Foundation; either version 3 of the License, or (at your 12 option) any later version. 13 14 The GNU MPFR Library is distributed in the hope that it will be useful, but 15 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 16 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 17 License for more details. 18 19 You should have received a copy of the GNU Lesser General Public License 20 along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see 21 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc., 22 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */ 23 24 #include "mpfr-test.h" 25 26 #define LOGBITS_PER_BLOCK 4 27 #if GMP_NUMB_BITS < 32 28 #define BITS_PER_RANDCALL GMP_NUMB_BITS 29 #else 30 #define BITS_PER_RANDCALL 32 31 #endif 32 33 void 34 mpfr_random2 (mpfr_ptr x, mp_size_t size, mpfr_exp_t exp, 35 gmp_randstate_t rstate) 36 { 37 mp_size_t xn, k, ri; 38 unsigned long sh; 39 mp_limb_t *xp; 40 mp_limb_t elimb, ran, acc; 41 int ran_nbits, bit_pos, nb; 42 43 if (MPFR_UNLIKELY(size == 0)) 44 { 45 MPFR_SET_ZERO (x); 46 MPFR_SET_POS (x); 47 return ; 48 } 49 else if (size > 0) 50 { 51 MPFR_SET_POS (x); 52 } 53 else 54 { 55 MPFR_SET_NEG (x); 56 size = -size; 57 } 58 59 xn = MPFR_LIMB_SIZE (x); 60 xp = MPFR_MANT (x); 61 if (size > xn) 62 size = xn; 63 k = xn - size; 64 65 /* Code extracted from GMP, function mpn_random2, to avoid the use 66 of GMP's internal random state in MPFR */ 67 68 mpfr_rand_raw (&elimb, rstate, BITS_PER_RANDCALL); 69 ran = elimb; 70 71 /* Start off at a random bit position in the most significant limb. */ 72 bit_pos = GMP_NUMB_BITS - 1; 73 ran >>= 6; /* Ideally log2(GMP_NUMB_BITS) */ 74 ran_nbits = BITS_PER_RANDCALL - 6; /* Ideally - log2(GMP_NUMB_BITS) */ 75 76 /* Bit 0 of ran chooses string of ones/string of zeroes. 77 Make most significant limb be non-zero by setting bit 0 of RAN. */ 78 ran |= 1; 79 ri = xn - 1; 80 81 acc = 0; 82 while (ri >= k) 83 { 84 if (ran_nbits < LOGBITS_PER_BLOCK + 1) 85 { 86 mpfr_rand_raw (&elimb, rstate, BITS_PER_RANDCALL); 87 ran = elimb; 88 ran_nbits = BITS_PER_RANDCALL; 89 } 90 91 nb = (ran >> 1) % (1 << LOGBITS_PER_BLOCK) + 1; 92 if ((ran & 1) != 0) 93 { 94 /* Generate a string of nb ones. */ 95 if (nb > bit_pos) 96 { 97 xp[ri--] = acc | (((mp_limb_t) 2 << bit_pos) - 1); 98 bit_pos += GMP_NUMB_BITS; 99 bit_pos -= nb; 100 acc = ((~(mp_limb_t) 1) << bit_pos) & GMP_NUMB_MASK; 101 } 102 else 103 { 104 bit_pos -= nb; 105 acc |= (((mp_limb_t) 2 << nb) - 2) << bit_pos; 106 } 107 } 108 else 109 { 110 /* Generate a string of nb zeroes. */ 111 if (nb > bit_pos) 112 { 113 xp[ri--] = acc; 114 acc = 0; 115 bit_pos += GMP_NUMB_BITS; 116 } 117 bit_pos -= nb; 118 } 119 ran_nbits -= LOGBITS_PER_BLOCK + 1; 120 ran >>= LOGBITS_PER_BLOCK + 1; 121 } 122 123 /* Set mandatory most significant bit. */ 124 /* xp[xn - 1] |= MPFR_LIMB_HIGHBIT; */ 125 126 if (k != 0) 127 { 128 /* Clear last limbs */ 129 MPN_ZERO (xp, k); 130 } 131 else 132 { 133 /* Mask off non significant bits in the low limb. */ 134 MPFR_UNSIGNED_MINUS_MODULO (sh, MPFR_PREC (x)); 135 xp[0] &= ~MPFR_LIMB_MASK (sh); 136 } 137 138 /* Generate random exponent. */ 139 mpfr_rand_raw (&elimb, RANDS, GMP_NUMB_BITS); 140 exp = ABS (exp); 141 MPFR_SET_EXP (x, elimb % (2 * exp + 1) - exp); 142 143 return ; 144 } 145