Dmitry Kasatkin | cdec9cb | 2011-08-31 14:05:16 +0300 | [diff] [blame] | 1 | /* mpi-bit.c - MPI bit level fucntions |
| 2 | * Copyright (C) 1998, 1999 Free Software Foundation, Inc. |
| 3 | * |
| 4 | * This file is part of GnuPG. |
| 5 | * |
| 6 | * GnuPG is free software; you can redistribute it and/or modify |
| 7 | * it under the terms of the GNU General Public License as published by |
| 8 | * the Free Software Foundation; either version 2 of the License, or |
| 9 | * (at your option) any later version. |
| 10 | * |
| 11 | * GnuPG is distributed in the hope that it will be useful, |
| 12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 14 | * GNU General Public License for more details. |
| 15 | * |
| 16 | * You should have received a copy of the GNU General Public License |
| 17 | * along with this program; if not, write to the Free Software |
| 18 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA |
| 19 | */ |
| 20 | |
| 21 | #include "mpi-internal.h" |
| 22 | #include "longlong.h" |
| 23 | |
Dmitry Kasatkin | cdec9cb | 2011-08-31 14:05:16 +0300 | [diff] [blame] | 24 | #define A_LIMB_1 ((mpi_limb_t) 1) |
| 25 | |
| 26 | /**************** |
| 27 | * Sometimes we have MSL (most significant limbs) which are 0; |
| 28 | * this is for some reasons not good, so this function removes them. |
| 29 | */ |
| 30 | void mpi_normalize(MPI a) |
| 31 | { |
| 32 | for (; a->nlimbs && !a->d[a->nlimbs - 1]; a->nlimbs--) |
| 33 | ; |
| 34 | } |
| 35 | |
| 36 | /**************** |
| 37 | * Return the number of bits in A. |
| 38 | */ |
| 39 | unsigned mpi_get_nbits(MPI a) |
| 40 | { |
| 41 | unsigned n; |
| 42 | |
| 43 | mpi_normalize(a); |
| 44 | |
| 45 | if (a->nlimbs) { |
| 46 | mpi_limb_t alimb = a->d[a->nlimbs - 1]; |
| 47 | if (alimb) |
| 48 | count_leading_zeros(n, alimb); |
| 49 | else |
| 50 | n = BITS_PER_MPI_LIMB; |
| 51 | n = BITS_PER_MPI_LIMB - n + (a->nlimbs - 1) * BITS_PER_MPI_LIMB; |
| 52 | } else |
| 53 | n = 0; |
| 54 | return n; |
| 55 | } |
| 56 | EXPORT_SYMBOL_GPL(mpi_get_nbits); |
| 57 | |
| 58 | /**************** |
| 59 | * Test whether bit N is set. |
| 60 | */ |
| 61 | int mpi_test_bit(MPI a, unsigned n) |
| 62 | { |
| 63 | unsigned limbno, bitno; |
| 64 | mpi_limb_t limb; |
| 65 | |
| 66 | limbno = n / BITS_PER_MPI_LIMB; |
| 67 | bitno = n % BITS_PER_MPI_LIMB; |
| 68 | |
| 69 | if (limbno >= a->nlimbs) |
| 70 | return 0; /* too far left: this is a 0 */ |
| 71 | limb = a->d[limbno]; |
| 72 | return (limb & (A_LIMB_1 << bitno)) ? 1 : 0; |
| 73 | } |
| 74 | |
| 75 | /**************** |
| 76 | * Set bit N of A. |
| 77 | */ |
| 78 | int mpi_set_bit(MPI a, unsigned n) |
| 79 | { |
| 80 | unsigned limbno, bitno; |
| 81 | |
| 82 | limbno = n / BITS_PER_MPI_LIMB; |
| 83 | bitno = n % BITS_PER_MPI_LIMB; |
| 84 | |
| 85 | if (limbno >= a->nlimbs) { /* resize */ |
| 86 | if (a->alloced >= limbno) |
| 87 | if (mpi_resize(a, limbno + 1) < 0) |
| 88 | return -ENOMEM; |
| 89 | a->nlimbs = limbno + 1; |
| 90 | } |
| 91 | a->d[limbno] |= (A_LIMB_1 << bitno); |
| 92 | return 0; |
| 93 | } |
| 94 | |
| 95 | /**************** |
| 96 | * Set bit N of A. and clear all bits above |
| 97 | */ |
| 98 | int mpi_set_highbit(MPI a, unsigned n) |
| 99 | { |
| 100 | unsigned limbno, bitno; |
| 101 | |
| 102 | limbno = n / BITS_PER_MPI_LIMB; |
| 103 | bitno = n % BITS_PER_MPI_LIMB; |
| 104 | |
| 105 | if (limbno >= a->nlimbs) { /* resize */ |
| 106 | if (a->alloced >= limbno) |
| 107 | if (mpi_resize(a, limbno + 1) < 0) |
| 108 | return -ENOMEM; |
| 109 | a->nlimbs = limbno + 1; |
| 110 | } |
| 111 | a->d[limbno] |= (A_LIMB_1 << bitno); |
| 112 | for (bitno++; bitno < BITS_PER_MPI_LIMB; bitno++) |
| 113 | a->d[limbno] &= ~(A_LIMB_1 << bitno); |
| 114 | a->nlimbs = limbno + 1; |
| 115 | return 0; |
| 116 | } |
| 117 | |
| 118 | /**************** |
| 119 | * clear bit N of A and all bits above |
| 120 | */ |
| 121 | void mpi_clear_highbit(MPI a, unsigned n) |
| 122 | { |
| 123 | unsigned limbno, bitno; |
| 124 | |
| 125 | limbno = n / BITS_PER_MPI_LIMB; |
| 126 | bitno = n % BITS_PER_MPI_LIMB; |
| 127 | |
| 128 | if (limbno >= a->nlimbs) |
| 129 | return; /* not allocated, so need to clear bits :-) */ |
| 130 | |
| 131 | for (; bitno < BITS_PER_MPI_LIMB; bitno++) |
| 132 | a->d[limbno] &= ~(A_LIMB_1 << bitno); |
| 133 | a->nlimbs = limbno + 1; |
| 134 | } |
| 135 | |
| 136 | /**************** |
| 137 | * Clear bit N of A. |
| 138 | */ |
| 139 | void mpi_clear_bit(MPI a, unsigned n) |
| 140 | { |
| 141 | unsigned limbno, bitno; |
| 142 | |
| 143 | limbno = n / BITS_PER_MPI_LIMB; |
| 144 | bitno = n % BITS_PER_MPI_LIMB; |
| 145 | |
| 146 | if (limbno >= a->nlimbs) |
| 147 | return; /* don't need to clear this bit, it's to far to left */ |
| 148 | a->d[limbno] &= ~(A_LIMB_1 << bitno); |
| 149 | } |
| 150 | |
| 151 | /**************** |
| 152 | * Shift A by N bits to the right |
| 153 | * FIXME: should use alloc_limb if X and A are same. |
| 154 | */ |
| 155 | int mpi_rshift(MPI x, MPI a, unsigned n) |
| 156 | { |
| 157 | mpi_ptr_t xp; |
| 158 | mpi_size_t xsize; |
| 159 | |
| 160 | xsize = a->nlimbs; |
| 161 | x->sign = a->sign; |
| 162 | if (RESIZE_IF_NEEDED(x, (size_t) xsize) < 0) |
| 163 | return -ENOMEM; |
| 164 | xp = x->d; |
| 165 | |
| 166 | if (xsize) { |
| 167 | mpihelp_rshift(xp, a->d, xsize, n); |
| 168 | MPN_NORMALIZE(xp, xsize); |
| 169 | } |
| 170 | x->nlimbs = xsize; |
| 171 | return 0; |
| 172 | } |
| 173 | |
| 174 | /**************** |
| 175 | * Shift A by COUNT limbs to the left |
| 176 | * This is used only within the MPI library |
| 177 | */ |
| 178 | int mpi_lshift_limbs(MPI a, unsigned int count) |
| 179 | { |
| 180 | mpi_ptr_t ap = a->d; |
| 181 | int n = a->nlimbs; |
| 182 | int i; |
| 183 | |
| 184 | if (!count || !n) |
| 185 | return 0; |
| 186 | |
| 187 | if (RESIZE_IF_NEEDED(a, n + count) < 0) |
| 188 | return -ENOMEM; |
| 189 | |
| 190 | for (i = n - 1; i >= 0; i--) |
| 191 | ap[i + count] = ap[i]; |
| 192 | for (i = 0; i < count; i++) |
| 193 | ap[i] = 0; |
| 194 | a->nlimbs += count; |
| 195 | return 0; |
| 196 | } |
| 197 | |
| 198 | /**************** |
| 199 | * Shift A by COUNT limbs to the right |
| 200 | * This is used only within the MPI library |
| 201 | */ |
| 202 | void mpi_rshift_limbs(MPI a, unsigned int count) |
| 203 | { |
| 204 | mpi_ptr_t ap = a->d; |
| 205 | mpi_size_t n = a->nlimbs; |
| 206 | unsigned int i; |
| 207 | |
| 208 | if (count >= n) { |
| 209 | a->nlimbs = 0; |
| 210 | return; |
| 211 | } |
| 212 | |
| 213 | for (i = 0; i < n - count; i++) |
| 214 | ap[i] = ap[i + count]; |
| 215 | ap[i] = 0; |
| 216 | a->nlimbs -= count; |
| 217 | } |