1 /* mpi-bit.c - MPI bit level functions 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 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 EXPORT_SYMBOL_GPL(mpi_normalize); 36 37 /**************** 38 * Return the number of bits in A. 39 */ 40 unsigned mpi_get_nbits(MPI a) 41 { 42 unsigned n; 43 44 mpi_normalize(a); 45 46 if (a->nlimbs) { 47 mpi_limb_t alimb = a->d[a->nlimbs - 1]; 48 if (alimb) 49 n = count_leading_zeros(alimb); 50 else 51 n = BITS_PER_MPI_LIMB; 52 n = BITS_PER_MPI_LIMB - n + (a->nlimbs - 1) * BITS_PER_MPI_LIMB; 53 } else 54 n = 0; 55 return n; 56 } 57 EXPORT_SYMBOL_GPL(mpi_get_nbits); 58 59 /**************** 60 * Test whether bit N is set. 61 */ 62 int mpi_test_bit(MPI a, unsigned int n) 63 { 64 unsigned int limbno, bitno; 65 mpi_limb_t limb; 66 67 limbno = n / BITS_PER_MPI_LIMB; 68 bitno = n % BITS_PER_MPI_LIMB; 69 70 if (limbno >= a->nlimbs) 71 return 0; /* too far left: this is a 0 */ 72 limb = a->d[limbno]; 73 return (limb & (A_LIMB_1 << bitno)) ? 1 : 0; 74 } 75 EXPORT_SYMBOL_GPL(mpi_test_bit); 76 77 /**************** 78 * Set bit N of A. 79 */ 80 void mpi_set_bit(MPI a, unsigned int n) 81 { 82 unsigned int i, limbno, bitno; 83 84 limbno = n / BITS_PER_MPI_LIMB; 85 bitno = n % BITS_PER_MPI_LIMB; 86 87 if (limbno >= a->nlimbs) { 88 for (i = a->nlimbs; i < a->alloced; i++) 89 a->d[i] = 0; 90 mpi_resize(a, limbno+1); 91 a->nlimbs = limbno+1; 92 } 93 a->d[limbno] |= (A_LIMB_1<<bitno); 94 } 95 96 /**************** 97 * Set bit N of A. and clear all bits above 98 */ 99 void mpi_set_highbit(MPI a, unsigned int n) 100 { 101 unsigned int i, limbno, bitno; 102 103 limbno = n / BITS_PER_MPI_LIMB; 104 bitno = n % BITS_PER_MPI_LIMB; 105 106 if (limbno >= a->nlimbs) { 107 for (i = a->nlimbs; i < a->alloced; i++) 108 a->d[i] = 0; 109 mpi_resize(a, limbno+1); 110 a->nlimbs = limbno+1; 111 } 112 a->d[limbno] |= (A_LIMB_1<<bitno); 113 for (bitno++; bitno < BITS_PER_MPI_LIMB; bitno++) 114 a->d[limbno] &= ~(A_LIMB_1 << bitno); 115 a->nlimbs = limbno+1; 116 } 117 EXPORT_SYMBOL_GPL(mpi_set_highbit); 118 119 /**************** 120 * clear bit N of A and all bits above 121 */ 122 void mpi_clear_highbit(MPI a, unsigned int n) 123 { 124 unsigned int limbno, bitno; 125 126 limbno = n / BITS_PER_MPI_LIMB; 127 bitno = n % BITS_PER_MPI_LIMB; 128 129 if (limbno >= a->nlimbs) 130 return; /* not allocated, therefore no need to clear bits :-) */ 131 132 for ( ; bitno < BITS_PER_MPI_LIMB; bitno++) 133 a->d[limbno] &= ~(A_LIMB_1 << bitno); 134 a->nlimbs = limbno+1; 135 } 136 137 /**************** 138 * Clear bit N of A. 139 */ 140 void mpi_clear_bit(MPI a, unsigned int n) 141 { 142 unsigned int limbno, bitno; 143 144 limbno = n / BITS_PER_MPI_LIMB; 145 bitno = n % BITS_PER_MPI_LIMB; 146 147 if (limbno >= a->nlimbs) 148 return; /* Don't need to clear this bit, it's far too left. */ 149 a->d[limbno] &= ~(A_LIMB_1 << bitno); 150 } 151 EXPORT_SYMBOL_GPL(mpi_clear_bit); 152 153 154 /**************** 155 * Shift A by COUNT limbs to the right 156 * This is used only within the MPI library 157 */ 158 void mpi_rshift_limbs(MPI a, unsigned int count) 159 { 160 mpi_ptr_t ap = a->d; 161 mpi_size_t n = a->nlimbs; 162 unsigned int i; 163 164 if (count >= n) { 165 a->nlimbs = 0; 166 return; 167 } 168 169 for (i = 0; i < n - count; i++) 170 ap[i] = ap[i+count]; 171 ap[i] = 0; 172 a->nlimbs -= count; 173 } 174 175 /* 176 * Shift A by N bits to the right. 177 */ 178 void mpi_rshift(MPI x, MPI a, unsigned int n) 179 { 180 mpi_size_t xsize; 181 unsigned int i; 182 unsigned int nlimbs = (n/BITS_PER_MPI_LIMB); 183 unsigned int nbits = (n%BITS_PER_MPI_LIMB); 184 185 if (x == a) { 186 /* In-place operation. */ 187 if (nlimbs >= x->nlimbs) { 188 x->nlimbs = 0; 189 return; 190 } 191 192 if (nlimbs) { 193 for (i = 0; i < x->nlimbs - nlimbs; i++) 194 x->d[i] = x->d[i+nlimbs]; 195 x->d[i] = 0; 196 x->nlimbs -= nlimbs; 197 } 198 if (x->nlimbs && nbits) 199 mpihelp_rshift(x->d, x->d, x->nlimbs, nbits); 200 } else if (nlimbs) { 201 /* Copy and shift by more or equal bits than in a limb. */ 202 xsize = a->nlimbs; 203 x->sign = a->sign; 204 RESIZE_IF_NEEDED(x, xsize); 205 x->nlimbs = xsize; 206 for (i = 0; i < a->nlimbs; i++) 207 x->d[i] = a->d[i]; 208 x->nlimbs = i; 209 210 if (nlimbs >= x->nlimbs) { 211 x->nlimbs = 0; 212 return; 213 } 214 215 for (i = 0; i < x->nlimbs - nlimbs; i++) 216 x->d[i] = x->d[i+nlimbs]; 217 x->d[i] = 0; 218 x->nlimbs -= nlimbs; 219 220 if (x->nlimbs && nbits) 221 mpihelp_rshift(x->d, x->d, x->nlimbs, nbits); 222 } else { 223 /* Copy and shift by less than bits in a limb. */ 224 xsize = a->nlimbs; 225 x->sign = a->sign; 226 RESIZE_IF_NEEDED(x, xsize); 227 x->nlimbs = xsize; 228 229 if (xsize) { 230 if (nbits) 231 mpihelp_rshift(x->d, a->d, x->nlimbs, nbits); 232 else { 233 /* The rshift helper function is not specified for 234 * NBITS==0, thus we do a plain copy here. 235 */ 236 for (i = 0; i < x->nlimbs; i++) 237 x->d[i] = a->d[i]; 238 } 239 } 240 } 241 MPN_NORMALIZE(x->d, x->nlimbs); 242 } 243 EXPORT_SYMBOL_GPL(mpi_rshift); 244 245 /**************** 246 * Shift A by COUNT limbs to the left 247 * This is used only within the MPI library 248 */ 249 void mpi_lshift_limbs(MPI a, unsigned int count) 250 { 251 mpi_ptr_t ap; 252 int n = a->nlimbs; 253 int i; 254 255 if (!count || !n) 256 return; 257 258 RESIZE_IF_NEEDED(a, n+count); 259 260 ap = a->d; 261 for (i = n-1; i >= 0; i--) 262 ap[i+count] = ap[i]; 263 for (i = 0; i < count; i++) 264 ap[i] = 0; 265 a->nlimbs += count; 266 } 267 268 /* 269 * Shift A by N bits to the left. 270 */ 271 void mpi_lshift(MPI x, MPI a, unsigned int n) 272 { 273 unsigned int nlimbs = (n/BITS_PER_MPI_LIMB); 274 unsigned int nbits = (n%BITS_PER_MPI_LIMB); 275 276 if (x == a && !n) 277 return; /* In-place shift with an amount of zero. */ 278 279 if (x != a) { 280 /* Copy A to X. */ 281 unsigned int alimbs = a->nlimbs; 282 int asign = a->sign; 283 mpi_ptr_t xp, ap; 284 285 RESIZE_IF_NEEDED(x, alimbs+nlimbs+1); 286 xp = x->d; 287 ap = a->d; 288 MPN_COPY(xp, ap, alimbs); 289 x->nlimbs = alimbs; 290 x->flags = a->flags; 291 x->sign = asign; 292 } 293 294 if (nlimbs && !nbits) { 295 /* Shift a full number of limbs. */ 296 mpi_lshift_limbs(x, nlimbs); 297 } else if (n) { 298 /* We use a very dump approach: Shift left by the number of 299 * limbs plus one and than fix it up by an rshift. 300 */ 301 mpi_lshift_limbs(x, nlimbs+1); 302 mpi_rshift(x, x, BITS_PER_MPI_LIMB - nbits); 303 } 304 305 MPN_NORMALIZE(x->d, x->nlimbs); 306 } 307