1/* mpi-bit.c - MPI bit level functions 2 * Copyright (C) 1998, 1999, 2001, 2002, 2006 Free Software Foundation, Inc. 3 * 4 * This file is part of Libgcrypt. 5 * 6 * Libgcrypt is free software; you can redistribute it and/or modify 7 * it under the terms of the GNU Lesser General Public License as 8 * published by the Free Software Foundation; either version 2.1 of 9 * the License, or (at your option) any later version. 10 * 11 * Libgcrypt 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 Lesser General Public License for more details. 15 * 16 * You should have received a copy of the GNU Lesser General Public 17 * License 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 <config.h> 22#include <stdio.h> 23#include <stdlib.h> 24#include "mpi-internal.h" 25#include "longlong.h" 26 27 28#ifdef MPI_INTERNAL_NEED_CLZ_TAB 29#ifdef __STDC__ 30const 31#endif 32unsigned char 33_gcry_clz_tab[] = 34{ 35 0,1,2,2,3,3,3,3,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5, 36 6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6, 37 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7, 38 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7, 39 8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8, 40 8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8, 41 8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8, 42 8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8, 43}; 44#endif 45 46 47#define A_LIMB_1 ((mpi_limb_t)1) 48 49 50/**************** 51 * Sometimes we have MSL (most significant limbs) which are 0; 52 * this is for some reasons not good, so this function removes them. 53 */ 54void 55_gcry_mpi_normalize( gcry_mpi_t a ) 56{ 57 if( mpi_is_opaque(a) ) 58 return; 59 60 for( ; a->nlimbs && !a->d[a->nlimbs-1]; a->nlimbs-- ) 61 ; 62} 63 64 65 66/**************** 67 * Return the number of bits in A. 68 */ 69unsigned int 70gcry_mpi_get_nbits( gcry_mpi_t a ) 71{ 72 unsigned n; 73 74 if( mpi_is_opaque(a) ) { 75 return a->sign; /* which holds the number of bits */ 76 } 77 78 _gcry_mpi_normalize( a ); 79 if( a->nlimbs ) { 80 mpi_limb_t alimb = a->d[a->nlimbs-1]; 81 if( alimb ) 82 count_leading_zeros( n, alimb ); 83 else 84 n = BITS_PER_MPI_LIMB; 85 n = BITS_PER_MPI_LIMB - n + (a->nlimbs-1) * BITS_PER_MPI_LIMB; 86 } 87 else 88 n = 0; 89 return n; 90} 91 92 93/**************** 94 * Test whether bit N is set. 95 */ 96int 97gcry_mpi_test_bit( gcry_mpi_t a, unsigned int n ) 98{ 99 unsigned int limbno, bitno; 100 mpi_limb_t limb; 101 102 limbno = n / BITS_PER_MPI_LIMB; 103 bitno = n % BITS_PER_MPI_LIMB; 104 105 if( limbno >= a->nlimbs ) 106 return 0; /* too far left: this is a 0 */ 107 limb = a->d[limbno]; 108 return (limb & (A_LIMB_1 << bitno))? 1: 0; 109} 110 111 112/**************** 113 * Set bit N of A. 114 */ 115void 116gcry_mpi_set_bit( gcry_mpi_t a, unsigned int n ) 117{ 118 unsigned int limbno, bitno; 119 120 limbno = n / BITS_PER_MPI_LIMB; 121 bitno = n % BITS_PER_MPI_LIMB; 122 123 if ( limbno >= a->nlimbs ) 124 { 125 mpi_resize (a, limbno+1 ); 126 a->nlimbs = limbno+1; 127 } 128 a->d[limbno] |= (A_LIMB_1<<bitno); 129} 130 131/**************** 132 * Set bit N of A. and clear all bits above 133 */ 134void 135gcry_mpi_set_highbit( gcry_mpi_t a, unsigned int n ) 136{ 137 unsigned int limbno, bitno; 138 139 limbno = n / BITS_PER_MPI_LIMB; 140 bitno = n % BITS_PER_MPI_LIMB; 141 142 if ( limbno >= a->nlimbs ) 143 { 144 mpi_resize (a, limbno+1 ); 145 a->nlimbs = limbno+1; 146 } 147 a->d[limbno] |= (A_LIMB_1<<bitno); 148 for ( bitno++; bitno < BITS_PER_MPI_LIMB; bitno++ ) 149 a->d[limbno] &= ~(A_LIMB_1 << bitno); 150 a->nlimbs = limbno+1; 151} 152 153/**************** 154 * clear bit N of A and all bits above 155 */ 156void 157gcry_mpi_clear_highbit( gcry_mpi_t a, unsigned int n ) 158{ 159 unsigned int limbno, bitno; 160 161 limbno = n / BITS_PER_MPI_LIMB; 162 bitno = n % BITS_PER_MPI_LIMB; 163 164 if( limbno >= a->nlimbs ) 165 return; /* not allocated, therefore no need to clear bits 166 :-) */ 167 168 for( ; bitno < BITS_PER_MPI_LIMB; bitno++ ) 169 a->d[limbno] &= ~(A_LIMB_1 << bitno); 170 a->nlimbs = limbno+1; 171} 172 173/**************** 174 * Clear bit N of A. 175 */ 176void 177gcry_mpi_clear_bit( gcry_mpi_t a, unsigned int n ) 178{ 179 unsigned int limbno, bitno; 180 181 limbno = n / BITS_PER_MPI_LIMB; 182 bitno = n % BITS_PER_MPI_LIMB; 183 184 if( limbno >= a->nlimbs ) 185 return; /* don't need to clear this bit, it's to far to left */ 186 a->d[limbno] &= ~(A_LIMB_1 << bitno); 187} 188 189 190/**************** 191 * Shift A by COUNT limbs to the right 192 * This is used only within the MPI library 193 */ 194void 195_gcry_mpi_rshift_limbs( gcry_mpi_t a, unsigned int count ) 196{ 197 mpi_ptr_t ap = a->d; 198 mpi_size_t n = a->nlimbs; 199 unsigned int i; 200 201 if( count >= n ) { 202 a->nlimbs = 0; 203 return; 204 } 205 206 for( i = 0; i < n - count; i++ ) 207 ap[i] = ap[i+count]; 208 ap[i] = 0; 209 a->nlimbs -= count; 210} 211 212 213/* 214 * Shift A by N bits to the right. 215 */ 216void 217gcry_mpi_rshift ( gcry_mpi_t x, gcry_mpi_t a, unsigned int n ) 218{ 219 mpi_size_t xsize; 220 unsigned int i; 221 unsigned int nlimbs = (n/BITS_PER_MPI_LIMB); 222 unsigned int nbits = (n%BITS_PER_MPI_LIMB); 223 224 if ( x == a ) 225 { 226 /* In-place operation. */ 227 if ( nlimbs >= x->nlimbs ) 228 { 229 x->nlimbs = 0; 230 return; 231 } 232 233 if (nlimbs) 234 { 235 for (i=0; i < x->nlimbs - nlimbs; i++ ) 236 x->d[i] = x->d[i+nlimbs]; 237 x->d[i] = 0; 238 x->nlimbs -= nlimbs; 239 240 } 241 if ( x->nlimbs && nbits ) 242 _gcry_mpih_rshift ( x->d, x->d, x->nlimbs, nbits ); 243 } 244 else if ( nlimbs ) 245 { 246 /* Copy and shift by more or equal bits than in a limb. */ 247 xsize = a->nlimbs; 248 x->sign = a->sign; 249 RESIZE_IF_NEEDED (x, xsize); 250 x->nlimbs = xsize; 251 for (i=0; i < a->nlimbs; i++ ) 252 x->d[i] = a->d[i]; 253 x->nlimbs = i; 254 255 if ( nlimbs >= x->nlimbs ) 256 { 257 x->nlimbs = 0; 258 return; 259 } 260 261 if (nlimbs) 262 { 263 for (i=0; i < x->nlimbs - nlimbs; i++ ) 264 x->d[i] = x->d[i+nlimbs]; 265 x->d[i] = 0; 266 x->nlimbs -= nlimbs; 267 } 268 269 if ( x->nlimbs && nbits ) 270 _gcry_mpih_rshift ( x->d, x->d, x->nlimbs, nbits ); 271 } 272 else 273 { 274 /* Copy and shift by less than bits in a limb. */ 275 xsize = a->nlimbs; 276 x->sign = a->sign; 277 RESIZE_IF_NEEDED (x, xsize); 278 x->nlimbs = xsize; 279 280 if ( xsize ) 281 { 282 if (nbits ) 283 _gcry_mpih_rshift (x->d, a->d, x->nlimbs, nbits ); 284 else 285 { 286 /* The rshift helper function is not specified for 287 NBITS==0, thus we do a plain copy here. */ 288 for (i=0; i < x->nlimbs; i++ ) 289 x->d[i] = a->d[i]; 290 } 291 } 292 } 293 MPN_NORMALIZE (x->d, x->nlimbs); 294} 295 296 297/**************** 298 * Shift A by COUNT limbs to the left 299 * This is used only within the MPI library 300 */ 301void 302_gcry_mpi_lshift_limbs (gcry_mpi_t a, unsigned int count) 303{ 304 mpi_ptr_t ap; 305 int n = a->nlimbs; 306 int i; 307 308 if (!count || !n) 309 return; 310 311 RESIZE_IF_NEEDED (a, n+count); 312 313 ap = a->d; 314 for (i = n-1; i >= 0; i--) 315 ap[i+count] = ap[i]; 316 for (i=0; i < count; i++ ) 317 ap[i] = 0; 318 a->nlimbs += count; 319} 320 321 322/* 323 * Shift A by N bits to the left. 324 */ 325void 326gcry_mpi_lshift ( gcry_mpi_t x, gcry_mpi_t a, unsigned int n ) 327{ 328 unsigned int nlimbs = (n/BITS_PER_MPI_LIMB); 329 unsigned int nbits = (n%BITS_PER_MPI_LIMB); 330 331 if (x == a && !n) 332 return; /* In-place shift with an amount of zero. */ 333 334 if ( x != a ) 335 { 336 /* Copy A to X. */ 337 unsigned int alimbs = a->nlimbs; 338 int asign = a->sign; 339 mpi_ptr_t xp, ap; 340 341 RESIZE_IF_NEEDED (x, alimbs+nlimbs+1); 342 xp = x->d; 343 ap = a->d; 344 MPN_COPY (xp, ap, alimbs); 345 x->nlimbs = alimbs; 346 x->flags = a->flags; 347 x->sign = asign; 348 } 349 350 if (nlimbs && !nbits) 351 { 352 /* Shift a full number of limbs. */ 353 _gcry_mpi_lshift_limbs (x, nlimbs); 354 } 355 else if (n) 356 { 357 /* We use a very dump approach: Shift left by the number of 358 limbs plus one and than fix it up by an rshift. */ 359 _gcry_mpi_lshift_limbs (x, nlimbs+1); 360 gcry_mpi_rshift (x, x, BITS_PER_MPI_LIMB - nbits); 361 } 362 363 MPN_NORMALIZE (x->d, x->nlimbs); 364} 365